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d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.2.2 Initial requests | Upon receipt of:
- an initial request for a dialog;
- a request for a standalone transaction, except the REGISTER method; or
- a request for an unknown method that does not relate to an existing dialog;
the IBCF shall:
1) if the request is an INVITE request, respond with a 100 (Trying) provisional response;
1A) remove its own SIP URI from the topmost Route header field;
2) if the request is an INVITE request and the IBCF is configured to perform application level gateway and/or transport plane control functionalities, save the Contact, CSeq and Record-Route header field values received in the request such that the IBCF is able to release the session if needed;
2A) If the request is a SUBSCRIBE and the IBCF does not need to act as B2BUA, based on operator policy, the IBCF shall determine whether or not to retain, for the related subscription, the SIP dialog state information and the duration information;
NOTE 1: The event package name can be taken into account to decide whether or not the SIP dialog state and the subscription duration information needs to be retained.
NOTE 2: The IBCF needs to insert its own URI in Record-Route of the initial SUBSCRIBE request and all subsequent NOTIFY requests if it decides to retain the SIP dialog state information.
2B) if the request is an initial request for a dialog and local policy requires the application of IBCF capabilities in subsequent requests, perform record route procedures as specified in RFC 3261 [26];
3) void;
4) void;
5) void;
5A) if the recipient of the request is understood from configured information to always send and receive private network traffic from this source, remove the P-Private-Network-Indication header field containing the domain name associated with that saved information;
6) store the values from the P-Charging-Function-Addresses header field, if present;
7) if the request is an initial request and "fe-identifier" header field parameter of P-Charging-Vector header field is applied in the operator domain;
- store the "fe-identifier" header field parameter in the P-Charging-Vector header field; and
- remove the "fe-identifier" header field parameter from the P-Charging-Vector header field;
8) remove some of the parameters from the P-Charging-Vector header field or the header field itself, depending on operator policy, if present;
9) remove the P-Charging-Function-Addresses header fields, if present; and
10) remove the Via "received-realm" header field parameter, as defined in RFC 8055 [208], if present, prior to forwarding the request;
and forward the request according to RFC 3261 [26].
NOTE 3: If IBCF processes a request without a pre-defined route (e.g. the subscription to reg event package originated by the P-CSCF), the next-hop address can be either obtained as specified in RFC 3263 [27A] or be provisioned in the IBCF.
When the IBCF receives an INVITE request, the IBCF may require the periodic refreshment of the session to avoid hung states in the IBCF. If the IBCF requires the session to be refreshed, the IBCF shall apply the procedures described in RFC 4028 [58] clause 8.
NOTE 4: Requesting the session to be refreshed requires support by at least one of the UEs. This functionality cannot automatically be granted, i.e. at least one of the involved UEs needs to support it.
When receiving a response to the initial request with a P-Charging-Vector header field, the IBCF acting as an exit point shall, if "fe-identifier" header field parameter of P-Charging-Vector header field is applied in the operator domain:
- remove any received "fe-identifier" header field parameter from the P-Charging-Vector header field; and
- add the "fe-identifier" header field parameter stored from the initial request to the P-Charging-Vector header field and add its own address or identifier as an "fe-addr" element of the "fe-identifier" header field parameter to the P-Charging-Vector header field.
With the exception of 305 (Use Proxy) responses, the IBCF shall not recurse on 3xx responses. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.2.3 Subsequent requests | Upon receipt of a subsequent request, the IBCF shall:
1) if the request is an INVITE request, respond with a 100 (Trying) provisional response;
1A) if the request is a NOTIFY request with the Subscription-State header field set to "terminated" and the IBCF has retained the SIP dialog state information for the associated subscription, once the NOTIFY transaction is terminated, the IBCF can remove all the stored information related to the associated subscription;
2) if the request is a target refresh request and the IBCF is configured to perform application level gateway and/or transport plane control functionalities, save the Contact and CSeq header field values received in the request such that the IBCF is able to release the session if needed; and
3) if the subsequent request is other than a target refresh request (including requests relating to an existing dialog where the method is unknown) and the IBCF is configured to perform application level gateway and/or transport plane control functionalities, save the Contact and CSeq header field values received in the request such that the IBCF is able to release the session if needed;
and forwards the request, based on the topmost Route header field, in accordance with the procedures of RFC 3261 [26]. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.2.4 IBCF-initiated call release | If the IBCF provides transport plane control functionality and receives an indication of a transport plane related error the IBCF may:
1) generate a BYE request for the terminating side based on information saved for the related dialog; and
2) generate a BYE request for the originating side based on the information saved for the related dialog.
NOTE: Transport plane related errors can be indicated from e.g. TrGW, or PCRF. The protocol for indicating transport plane related errors to the IBCF is out of scope of this specification.
Upon receipt of the 2xx responses for both BYE requests, the IBCF shall release all information related to the dialog and the related multimedia session. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.3 IBCF as an entry point | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.3.1 Registration | When IBCF receives a REGISTER request, the IBCF shall:
1) verify if it arrived from a trusted domain or not. If the request arrived from an untrusted domain, respond with 403 (Forbidden) response;
NOTE 1: The IBCF can find out whether the request arrived from a trusted domain or not, from the procedures described in 3GPP TS 33.210 [19A].
2) if network topology hiding, or screening of SIP signalling, is required or IBCF is configured to perform application level gateway and/or transport plane control functionalities, add its own routeable SIP URI to the top of the Path header field; and
NOTE 2: The IBCF can include in the inserted SIP URI an indicator that identifies the direction of subsequent requests received by the IBCF i.e., from the S-CSCF towards the P-CSCF, to identify the UE-terminating case. The IBCF can encode this indicator in different ways, such as, e.g., a unique parameter in the URI, a character string in the username part of the URI, or a dedicated port number in the URI.
NOTE 3: Any subsequent request that includes the direction indicator (in the Route header field) or arrives at the dedicated port number, indicates that the request was sent by the S-CSCF towards the P-CSCF.
3) If IBCF is colocated with an I-CSCF, or it has a preconfigured I-CSCF to be contacted, forward the request to that I-CSCF. Otherwise select an I-CSCF and forward the request to that I-CSCF.
NOTE 5: The selection of an I-CSCF can lead to additional delays.
If the selected I-CSCF:
- does not respond to the REGISTER request and its retransmissions by the IBCF; or
- sends back a 3xx response or 480 (Temporarily Unavailable) response to a REGISTER request;
the IBCF shall select a new I-CSCF and forward the REGISTER request to that I-CSCF.
NOTE 4: The list of the I-CSCFs can be either obtained as specified in RFC 3263 [27A] or provisioned in the IBCF.
If the IBCF fails to forward the REGISTER request to any I-CSCF, the IBCF shall send back a 504 (Server Time-Out) response towards the P-CSCF, in accordance with the procedures in RFC 3261 [26].
5.10.3.1A General
For all SIP transactions identified:
- if priority is supported (NOTE 1), as containing an authorised Resource-Priority header field or a temporarily authorised Resource-Priority header field, or, if such an option is supported, relating to a dialog which previously contained an authorised Resource-Priority header field;
the IBCF shall give priority over other transactions or dialogs. This allows special treatment of such transactions or dialogs. If priority is supported, the IBCF shall adjust the priority treatment of transactions or dialogs according to the most recently received authorized Resource-Priority header field or backwards indication value.
NOTE 1: For an INVITE request, various mechanisms can be applied to recognize the need for priority treatment (e.g., based on the dialled digits). The exact mechanisms are left to national regulation and network configuration.
Based on the alternative mechanism to recognize the need for priority treatment, the IBCF shall insert the temporarily authorised Resource-Priority header field with appropriate namespace and priority value in the INVITE request.
NOTE 2: The special treatment can include filtering, higher priority processing, routeing, call gapping. The exact meaning of priority is not defined further in this document, but is left to national regulation and network configuration.
Based on local policy, the IBCF acting as an entry point shall add in requests in the P-Charging-Vector header field a "transit-ioi" header field parameter with an entry which identifies the operator network which the request is transitting or with a void entry.
Based on local policy the IBCF shall delete or void in requests in the P-Charging-Vector header field any received "transit-ioi" header field parameter value.
NOTE 3: Only one "transit-ioi" header field parameter entry is added per transit network. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.3.2 Initial requests | Upon receipt of:
- an initial request for a dialog;
- a request for a standalone transaction except the REGISTER request; or
- a request for an unknown method that does not relate to an existing dialog;
the IBCF shall verify whether the request is arrived from a trusted domain or not. If the request arrived from an untrusted domain, then the IBCF shall:
- if the topmost Route header field of the request contains the "orig" parameter, respond with 403 (Forbidden) response.
Otherwise,
- remove all P-Charging-Vector header fields and all P-Charging-Function-Addresses header fields the request may contain; and
- remove all Feature-Caps header fields, if present.
Upon receipt of:
- an initial request for a dialog;
- a request for a standalone transaction except the REGISTER request; or
- a request for an unknown method that does not relate to an existing dialog;
the IBCF shall:
1) if the request is an INVITE request, then respond with a 100 (Trying) provisional response;
1A) if a P-Private-Network-Indication header field is included in the request, check whether the configured information allows the receipt of private network traffic from this source. If private network traffic is allowed, the IBCF shall check whether the received domain name in any included P-Private-Network-Indication header field in the request is the same as the domain name associated with that configured information. If private network traffic is not allowed, or the received domain name does not match, then the IBCF shall remove the P-Private-Network-Indication header field;
1B) if the initiator of the request is understood from configured information to always send and receive private network traffic from this source, insert a P-Private-Network-Indication header field containing the domain name associated with that configured information;
1C) remove its own SIP URI from the topmost Route header field;
2) if the request is an INVITE request and the IBCF is configured to perform application level gateway and/or transport plane control functionalities, then the IBCF shall save the Contact, CSeq and Record-Route header field values received in the request such that the IBCF is able to release the session if needed;
2A) If the request is a SUBSCRIBE and the IBCF does not need to act as B2BUA, based on operator policy, the IBCF shall determine whether or not to retain, for the related subscription, the SIP dialog state information and the duration information;
NOTE 1: The event package name can be taken into account to decide whether or not the SIP dialog state and the subscription duration information needs to be retained.
NOTE 2: The IBCF needs to insert its own URI in Record-Route of the initial SUBSCRIBE request and all subsequent NOTIFY requests if it decides to retain the SIP dialog state information.
2B) if the request is an initial request for a dialog and local policy requires the application of IBCF capabilities in subsequent requests, perform record route procedures as specified in RFC 3261 [26];
2C) if
- the request is an initial request for a dialog, or a standalone request, and
- the Request-URI contains an emergency service URN, i.e. a service URN with a top-level service type of "sos" as specified in RFC 5031 [69] and
- a P-Private-Network-Indication valid within the trust domain is not included, and
- based on local policy, no Route header field is remaining after step 1C) was executed,
then include a topmost Route header field set to the URI associated with an E-CSCF;
2D) if the network uses the Resource-Priority header field to control the priority of emergency calls, the IBCF shall add a Resource-Priority header field containing a namespace of "esnet" as defined in RFC 7135 [197];
3) void;
4) if IBCF receives an initial request for a dialog or standalone transaction, that contains a single Route header field pointing to itself, and it is co-located with an I-CSCF, or it has a preconfigured I-CSCF to be contacted, then forward the request to that I-CSCF. Otherwise select an I-CSCF and forward the request to that I-CSCF. If the single Route header field of the request contains the "orig" parameter, the IBCF shall insert the "orig" parameter to the URI of the I-CSCF;
NOTE 3: The selection of an I-CSCF can lead to additional delays.
5) if the request does not contain a Route header field or if it contains one or more Route header fields where the topmost Route header field does not contain the "orig" parameter, optionally – based on operator policy – append the "orig" parameter to the URI in the topmost Route header field of the next request sent from the IBCF to an entity of the IM CN subsystem for which it is an entry point;
NOTE 4: The appending of an "orig" parameter to the URI in the topmost Route header field enables an IM CN subsystem to perform originating services to the network that originated the initial request. The appending can be dependent on the network that originated the initial request as determined by e.g. origin IP address of the received request, etc.
6) if services that require knowledge of the adjacent network are provided within the network for which the IBCF is acting as an entry point, based on operator policy, insert a Via "received-realm" header field parameter, as defined in RFC 8055 [208];
6A) if the IBCF, acting as an entry point to a terminating visited network, PCRF based P-CSCF restoration procedures,
- the request contains a topmost Route header field pointing to a P-CSCF, and
- the IBCF considers the P-CSCF is in a non-working state,
remove all entries in the Route header field and add a Route header field set to the URI associated with an alternative P-CSCF;
NOTE 5: How the SIP URI of the alternative P-CSCF is obtained by the IBCF is implementation dependent. The IBCF can make sure that selected P-CSCF support the PCRF based P-CSCF restoration procedures based on local configuration.
NOTE 6: It is implementation dependent as to how the IBCF determines the P-CSCF is in non-working state.
7) if the initiator of the request is understood to always send and receive private network traffic:
NOTE 7: The IBCF can identify that a request is received from a source that always sends or receives private traffic by evaluating the TLS session or by other means.
a) add the identity of the initiator in a P-Served-User header field as defined in RFC 5502 [133] as a SIP URI identifying the initiator; and
NOTE 8: The IBCF can retrieve the identity of the initiator from the subjectCommonName (CN) if it is not present in the subjectAltName in the certificates during the TLS session setup in accordance with the procedures of RFC 5280 [213] or by other means.
b) if not already appended in 4) or 5) above, append the "orig" parameter to the URI in the topmost Route header field of the request sent from the IBCF to the entity of the IM CN subsystem for which it is an entry point;
8) if the request is an initial request and "fe-identifier" header field parameter of P-Charging-Vector header field is applied in the operator domain:
- remove any received "fe-identifier" header field parameter from the P-Charging-Vector header field; and
- add an "fe-addr" element in an "fe-identifier" header field parameter to the P-Charging-Vector header field with its own address or identifier; and
9) if the IBCF supports calling number verification using signature verification and attestation information as described in subclause 3.1 and no Identity header field is received in an initial INVITE or MESSAGE request, based on local policy insert:
a) an Attestation-Info header field specified in subclause 7.2.18 set to a value "C", specified in RFC 8588 [261]; and
b) an Origination-Id header field specified in subclause 7.2.19 containing an "origid" claim as specified in RFC 8588 [261] set to a value identifying the source of the request;
and forward the request according to RFC 3261 [26].
When the IBCF receives an INVITE request, the IBCF may require the periodic refreshment of the session to avoid hung states in the IBCF. If the IBCF requires the session to be refreshed, the IBCF shall apply the procedures described in RFC 4028 [58] clause 8.
NOTE 9: Requesting the session to be refreshed requires support by at least one of the UEs. This functionality cannot automatically be granted, i.e. at least one of the involved UEs needs to support it.
If the serving network supports HSS based P-CSCF restoration as specified in 3GPP TS 23.380 [7D], the IBCF is acting as an entry point to a terminating visited network and the IBCF does not receive any response within a configured time:
NOTE 10: The configurable time needs to be less than timer B and timer F.
1) to an initial INVITE request, then if the Route header field contains only one entry the IBCF shall in the 408 (Request Timeout) response include a Restoration-Info header field specified in subclause 7.2.11 containing the value "noresponse"; and
2) to an initial non-INVITE request for a dialog, a standalone transaction or an unknown method that does not relate to an existing dialog, then if the Route header field contains only one entry the IBCF shall send a 504 (Server Time-out) response include a Restoration-Info header field specified in subclause 7.2.11 containing the value "noresponse".
NOTE 11: The IBCF determines if it is acting as an entry point to a terminating visited network based on configuration or other data in the incoming request, or the "iotl" SIP URI parameter specified in RFC 7549 [225].
NOTE 12: If there is only one entry in the Route header field it represents either an MSC server or a P-CSCF. The S-CSCF will use the g.3gpp.ics media feature tag to determine if it is the MSC server or the P-CSCF.
When the IBCF receives a response to an initial request (e.g. 183 or 2xx), the IBCF shall:
1) store the values from the P-Charging-Function-Addresses header field, if present;
2) remove the "fe-identifier" header field parameter from the P-Charging-Vector header field, if present; and
3) remove the P-Charging-Function-Addresses header field prior to forwarding the message;
With the exception of 305 (Use Proxy) responses, the IBCF shall not recurse on 3xx responses. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.3.3 Subsequent requests | Upon receipt of a subsequent request, the IBCF shall:
1) if the request is an INVITE request, then respond with a 100 (Trying) provisional response;
1A) if the request is a NOTIFY request with the Subscription-State header field set to "terminated" and the IBCF has retained the SIP dialog state information for the associated subscription, once the NOTIFY transaction is terminated, the IBCF can remove all the stored information related to the associated subscription;
2) if the request is a target refresh request and the IBCF is configured to perform application level gateway and/or transport plane control functionalities, then the IBCF shall save the Contact and CSeq header field values received in the request such that the IBCF is able to release the session if needed;
3) if the subsequent request is other than a target refresh request (including requests relating to an existing dialog where the method is unknown) and the IBCF is configured to perform application level gateway and/or transport plane control functionalities, then the IBCF shall save the Contact and CSeq header field values received in the request such that the IBCF is able to release the session if needed;
4) void;
5) if the request is received from an untrusted domain, remove all Feature-Caps header fields, if present; and
6) if the subsequent request is received from an entity outside the trust domain, then the IBCF shall remove a P-Charging-Vector header field, if present;
and forwards the request, based on the topmost Route header field, in accordance with the procedures of RFC 3261 [26]. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.3.4 IBCF-initiated call release | If the IBCF provides transport plane control functionality and receives an indication of a transport plane related error the IBCF may:
1) generate a BYE request for the terminating side based on information saved for the related dialog; and
2) generate a BYE request for the originating side based on the information saved for the related dialog.
NOTE: Transport plane related errors can be indicated from e.g. TrGW or PCRF. The protocol for indicating transport plane related errors to the IBCF is out of scope of this specification.
Upon receipt of the 2xx responses for both BYE requests, the IBCF shall release all information related to the dialog and the related multimedia session. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.3.5 Abnormal cases | When the IBCF acting as an entry point in the originating home network is unable to forward a SIP request, as determined by one of the following:
NOTE 1: If IBCF supports indicating traffic leg associated with a URI as specified in RFC 7549 [225], the IBCF can determine that IBCF is acting as an entry point in the originating home network by inspecting the value of the "iotl" SIP URI parameter, if an "iotl" SIP URI is included in the SIP request.
- there is no response to the SIP request and its retransmissions by the IBCF; or
- by unspecified means available to the IBCF;
and:
- the IBCF supports S-CSCF restoration procedures;
then the IBCF:
1) shall reject the request by returning a 504 (Server Time-out) response; and
2) shall include in the 504 (Server Time-out) response:
- a Content-Type header field with the value set to associated MIME type of the 3GPP IM CN subsystem XML body as described in subclause 7.6.1;
- a P-Asserted-Identity header field set to the value of the SIP URI of the IBCF included in the Path header field during the registration (see subclause 5.10.3.1); and
- a 3GPP IM CN subsystem XML body containing:
a) an <ims-3gpp> element with the "version" attribute set to "1" and with an <alternative-service> child element, set to the parameters of the alternative service:
i) a <type> child element, set to "restoration" (see table 7.6.2) to indicate that restoration procedures are supported;
ii) a <reason> child element, set to an operator configurable reason; and
iii) an <action> child element, set to "initial-registration" (see table 7.6.3).
NOTE 2: These procedures do not prevent the usage of unspecified reliability or recovery techniques above and beyond those specified in this subclause. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.4 THIG functionality in the IBCF | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.4.1 General | NOTE 1: THIG functionality is performed in I-CSCF in Release-5 and Release-6 and is compatible with the procedures specified in this subclause.
The following procedures shall only be applied if network topology hiding is required by the network. The network requiring network topology hiding is called the hiding network.
NOTE 2: Requests and responses are handled independently therefore no state information is needed for that purpose within an IBCF.
The IBCF shall apply network topology hiding to all header fields which reveal topology information, such as Via, Route, Record-Route, Service-Route, and Path.
Upon receiving an incoming REGISTER request for which network topology hiding has to be applied and which includes a Path header field, the IBCF shall add the routeable SIP URI of the IBCF to the top of the Path header field. The IBCF may:
1) include in the inserted SIP URI an indicator that identifies the direction of subsequent requests received by the IBCF i.e., from the S-CSCF towards the P-CSCF, to identify the UE-terminating case. The IBCF may encode this indicator in different ways, such as, e.g., a unique parameter in the URI, a character string in the username part of the URI, or a dedicated port number in the URI; and
2) if:
a) IBCF supports indicating traffic leg associated with a URI as specified in RFC 7549 [225]; and
b) if the SIP URI in the bottommost hidden Path header field contains an "iotl" SIP URI parameter;
then append an "iotl" SIP URI parameter with the same value to its own SIP URI in the Path header field.
NOTE 3: Any subsequent request that includes the direction indicator (in the Route header field) or arrives at the dedicated port number, indicates that the request was sent by the S-CSCF towards the P-CSCF.
Upon receiving a 200 (OK) response to the REGISTER request and:
1. if the IBCF is located in the visited network; and
2. if the IBCF applied topology hiding on the Path header field contained in the REGISTER request;
the IBCF shall:
1. perform a decryption procedure, as described in subclause 5.10.4.3, on the received Path header field; and
2. insert a "+g.3gpp.thig-path" Feature-Caps header field parameter, as defined in subclause 7.9A.9, set to the same IBCF's SIP URI value as included in the Path header field of the REGISTER request sent to the home network.
NOTE 4: If a decryption of the Path header field contained in a 200 (OK) response on REGISTER request is not done then the UE will not perform restoration procedures if the P-CSCF rejects an initial request for a dialog or a request for a standalone transaction with a 504 (Server Time-out) response since there will be a mismatch between a SIP URI in the P-Asserted-Identity header field received in a valid 504 (Server Time-out) response and the SIP URIs the UE received in the Path header field.
Upon receiving an incoming initial request for which network topology hiding has to be applied and which includes a Record-Route header field, the IBCF shall add its own routeable SIP URI to the top of the Record-Route header field.
Upon receiving a 200 (OK) response to a REGISTER request for which network topology hiding has to be applied and which includes an URI identifying the IBCF in the topmost Service-Route header field and:
1) if IBCF supports indicating the traffic leg associated with a URI as specified in RFC 7549 [225]; and
2) if an "iotl" parameter is included in the bottommost SIP URI;
then append an "iotl" SIP URI parameter with the same value to its own SIP URI in the Service-Route header field.
When the home network IBCF receives a 504 (Server Time-out) response containing a P-Asserted-Identity header field set to the value of the S-CSCF's SIP URI for a roaming UE and if the home network is a hiding network then the IBCF shall replace the received P-Asserted-Identity header field with the P-Asserted-Identity header field set to the value of the own SIP URI.
NOTE 5: By provision or by obtaining from the corresponding request's Route header field, the IBCF deduces whether the received value of the P-Asserted-Identity header field in the 504 (Server Time-out) response is the value of S-CSCF's SIP URI. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.4.2 Encryption for network topology hiding | Upon receiving an outgoing request/response from the hiding network the IBCF shall perform the encryption for network topology hiding purposes, i.e. the IBCF shall:
0) if applying encryption procedure on the Service-Route header field, exclude from the Service-Route header field the entry corresponding to its own SIP URI and use the remaining header field values which were added by one or more specific entity of the hiding network as input to encryption and skip item 1) below;
NOTE 1: In accordance with the procedures described in RFC 3608 [38], the IBCF does not insert its own routable SIP URI to the Service-Route header field i.e. the SIP URI identifying the IBCF in the topmost entry of the Service-Route header field is inserted by the S-CSCF. However this entry is excluded from encryption and will stay in the topmost entry of the Service-Route header field i.e. before the topmost encrypted entry.
1) use the whole header field values which were added by one or more specific entity of the hiding network as input to encryption, besides the UE entry;
2) not change the order of the header fields subject to encryption when performing encryption;
3) use for one encrypted string all received consecutive header field entries subject to encryption, regardless if they appear in separate consecutive header fields or if they are consecutive entries in a comma separated list in one header field;
4) construct a hostname that is the encrypted string in a way that allows to identify the encrypting network's name (i.e. the IBCF network);
NOTE 2: This is to allow the IBCF to identify that itself has encrypted the string when subsequently receiving the encrypted string. The details of encoding the encrypting networks's name are not specified as the IBCF is the creator and consumer of this value. This is needed because header field parameters (like "tokenized-by") are not required to be preserved when creating a route set.
5) append a "tokenized-by" header field parameter and set it to the value of the encrypting network's name, after the constructed hostname;
6) form one valid entry for the specific header field out of the resulting NAI, e.g. prepend "SIP/2.0/UDP" for Via header fields or "sip:" for Path, Service-Route, Route and Record-Route header fields;
7) if the IBCF encrypted an entry in the Route header field, then it also inserts its own URI before the topmost encrypted entry; and
8) if the IBCF encrypted an entry in the Via header field, then it also inserts its own URI before the topmost encrypted entry.
NOTE 3: Even if consecutive entries of the same network in a specific header field are encrypted, they will result in only one encrypted header field entry. For example:
Via: SIP/2.0/UDP ibcf1.home1.net;lr,
SIP/2.0/UDP Token( SIP/2.0/UDP scscf1.home1.net;lr,
SIP/2.0/UDP pcscf1.home1.net;lr)@home1.net;
tokenized-by=home1.net,
SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]
NOTE 4: If multiple entries of the same network are within the same type of header fields, but they are not consecutive, then these entries will be tokenized to different strings. For example:
Record-Route: sip:ibcf1.home1.net;lr,
sip:Token(sip:scscf1.home1.net;lr)@home1.net;tokenized-by=home1.net,
sip:as1.foreign.net;lr,
sip:Token(sip:scscf1.home1.net;lr,
sip:pcscf1.home1.net;lr)@home1.net;tokenized-by=home1.net
NOTE 5: If request will return to the hiding network (e.g. after visiting an AS), then the URI of IBCF is inserted. For example:
Route: sip:as1.foreign.net;lr,
sip:ibcf1.home1.net;lr,
sip:Token(sip:scscf1.home1.net;lr);tokenized-by=home1.net |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.4.3 Decryption for network topology hiding | Upon receiving and incoming requests/response to the hiding network the IBCF shall perform the decryption for network topology hiding purposes, i.e. the IBCF shall:
1) identify hostnames encrypted by the network this IBCF belongs to within all header fields of the incoming message;
2) use those hostnames that carry the identification of the hiding network as input to decryption;
3) use as encrypted string the hostname which follows the sent-protocol (for Via header fields, e.g. "SIP/2.0/UDP") or the URI scheme (for Path, Route and Record-Route header fields, e.g. "sip:");
4) replace all content of the received header field which carries encrypted information with the entries resulting from decryption.
EXAMPLE: An encrypted entry to a Via header field that looks like:
Via: SIP/2.0/UDP Token(SIP/2.0/UDP scscf1.home1.net;lr,
SIP/2.0/UDP pcscf1.home1.net;lr);tokenized-by=home1.net
will be replaced with the following entries:
Via: SIP/2.0/UDP scscf1.home1.net;lr, SIP/2.0/UDP pcscf1.home1.net;lr
NOTE: Motivations for these decryption procedures are e.g. to allow the correct routeing of a response through the hiding network, to enable loop avoidance within the hiding network, or to allow the entities of the hiding network to change their entries within e.g. the Record-Route header field. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.5 IMS-ALG functionality in the IBCF | The IBCF shall only apply the following procedures if application level gateway functionality is required by the network.
The IBCF acts as a B2BUA when it performs IMS-ALG functionality. As an IMS-ALG, the IBCF will internally map the message header fields between the two dialogs that it manages. It is responsible for correlating the dialog identifiers and will decide when to simply translate a message from one dialog to the other, or when to perform other functions. The IBCF, although acting as a UA, does not initiate any registration of its associated addresses. These are assumed to be known by peer-to-peer arrangements within the IM CN subsystem.
An IBCF may replace a contact address with a URI of its own when the contact address in the incoming message is not a GRUU. In all other cases the IBCF shall use a GRUU (e.g when the contact address is an IP address).
The IBCF shall transparently forward a received Contact header field when the Contact header field contains a GRUU or a media feature tag is included indicating a capability for which the Contact URI can be used by the remote party. When transparently forwarding a received Contact header field of a dialog-forming request, the IBCF shall include its own URI in a Record-Route header field in order to ensure that it is included on the route of subsequent requests.
NOTE: One example of such a media feature tag is the isfocus media feature tag used by conference services to transport the temporary conference identity that can be used when rejoining an ongoing conference.
The internal function of the IBCF as an IMS-ALG is defined in 3GPP TS 29.162 [11A].
If the IBCF receives a message with a body part for a UE from an S-CSCF, and:
- if the body part is the 3GPP IM CN subsystem XML body (as indicated by the Content-Type header field, see subclause 7.6) and the body part is not optional (as indicated by the (absence of the) Content-Disposition header field); or
- if a header field that describes the body is present and the header field's value is not understood (e.g. Content-Language header field or Content-Encoding header field);
then the IBCF shall transparently forward the message with the body part and the header field(s) that describe the body part. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.6 Screening of SIP signalling | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.6.1 General | The IBCF may act as a B2BUA when it performs screening of SIP signalling functionality. In this case the B2BUA behaviour of the IBCF shall comply with the description given in subclause 5.10.5 for the IMS-ALG functionality.
NOTE: Many header fields are intended for end-to-end operation; removal of such header fields will impact the intended end-to-end operation between the end users. Additionally the IM CN subsystem does not preclude security mechanisms covering SIP header fields; any such removal can prevent validation of all header fields covered by the security mechanism. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.6.2 IBCF procedures for SIP header fields | If specified by local policy rules, the IBCF may omit or modify any received SIP header fields prior to forwarding SIP messages, with the following exceptions.
As a result of any screening policy adopted, the IBCF should not modify at least the following header fields which would cause misoperation of the IM CN subsystem:
- Authorization; and
- WWW-Authenticate.
Where the IBCF appears in the path between the UE and the S-CSCF, some header fields are involved in the registration and authentication of the user. As a result of any screening policy adopted as part of normal operation, e.g. where the request or response is forwarded on, the IBCF should not modify as part of the registration procedure at least the following header fields:
- Path; and
- Service-Route.
NOTE 1: If the IBCF modifies SIP information elements (SIP header fields, SIP message bodies) other than as specified by SIP procedures (e.g., RFC 3261 [26]) caution needs to be taken that SIP functionality (e.g., routeing using Route, Record-Route and Via) is not impacted in a way that could create interoperability problems with networks that assume that this information is not modified.
NOTE 2: Where operator requirements can be achieved by configuration hiding, then these procedures can be used in preference to screening.
The IBCF may add, remove, or modify, the P-Early-Media header field within forwarded SIP requests and responses according to procedures in RFC 5009 [109].
NOTE 3: The IBCF can use the P-Early-Media header field for the gate control procedures,by through-connect control as described in 3GPP TS 29.162 [11A]. In the presence of early media for multiple dialogs due to forking, if the IBCF is able to identify the media associated with a dialog, (i.e., if symmetric RTP is used by the UE and the IBCF can use the remote SDP information to determine the source of the media) the IBCF can selectively open the gate corresponding to an authorized early media flow for the selected media.
The IBCF may add, or omit any P-Asserted-Identity header fields prior to forwarding SIP messages according to local policy.
NOTE 4: The IBCF can use the P-Asserted-Identy header field to trigger identity specific procedures in subsequent entities, e.g. for malicious call identification. As an example, a P-Asserted-Identity header field will be deleted and a new P-Asserted-Identity header field with operator specific content will be added to the outgoing request, if the request was received from a network which cannot support the deletion of INFO request which is needed for the support of the malicious call identification service.
When the IBCF, located in the home network, receives a SIP request from another entity within the same trust domain, the IBCF may police the ICSI value contained in the P-Asserted-Service header field. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.6.3 IBCF procedures for SIP message bodies | If the IBCF acts as a B2BUA, and the IBCF receives a message with a body part for a UE from an S-CSCF, and:
- if the body part is the 3GPP IM CN subsystem XML body (as indicated by the Content-Type header field, see subclause 7.6) and the body part is not optional (as indicated by the (absence of the) Content-Disposition header field); or
- if a header field that describes the body is present and the header field's value is not understood (e.g. Content-Language header field or Content-Encoding header field),
then the IBCF shall transparently forward the message with the body part and the header field(s) that describe the body part.
If IP address translation (NA(P)T or IP version interworking) occurs on the user plane, the IBCF shall modify SDP according to subclause 6.7.1;
Additionally, the IBCF may take the followings action upon SIP message bodies:
1) examine the length of a SIP message body and if required by local policy, take an appropriate action (e.g. forward the message body transparently, reject the request, remove the body);
2) examine the characteristics of the SIP message body MIMEs (i.e. check the values of any Content-Type, Content-Disposition, and Content-Language header fields), take an appropriate action defined by local policy (e.g. forward the body unchanged, remove the SIP message body MIME, reject the call); and
3) examine the content of SIP message body MIMEs, and take appropriate action defined by local policy (e.g. forward the body unchanged, remove the SIP message body MIME, reject the call).
When the intended action of an IBCF, based on local policy, is to remove a message body MIME from a SIP message body, and a Content-Disposition header field with a "handling" parameter set to "required" is associated with the MIME, the IBCF shall reject the SIP request with the 415 (Unsupported Media Type) response code as specified in RFC 5621 [150]. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.7 Media transcoding control | The IBCF may perform the media transcoding control in order to allow establishing communication between IM CN subsystems using different media codecs based on the interworking agreement and session information. When performing media transcoding control the IBCF acts as a special case of an IMS-ALG compliant with the description given in subclause 5.10.5.
Upon receipt of any request containing an SDP offer, based on local policy and signalling inspection (e.g ICSI values, SDP), the IBCF may perform media transcoding control, as defined in subclause 6.7.1.3. Based on the local configuration determines the media which requires transcoding in the SDP offer. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.8 Privacy protection at the trust domain boundary | In order to ensure privacy IBCF shall additionally to what is specified in subclause 4.4 and before sending the SIP requests or SIP responses outside the trust domain boundary perform the privacy protection as specified in RFC 3323 [33] and RFC 7044 [66] applicable to header fields with the clarifications in this subclause. If there are any conflicts between topology hiding specified in subclause 5.10.4 and the procedures in this subclause, the topology hiding takes precedence over privacy protection.
NOTE: The privacy protection for the History-Info header field is performed in accordance with RFC 7044 [66] subclause 10.1.2.
If a Privacy header field with a value different from "none" is received the IBCF shall:
1) if "header" privacy is requested as specified in RFC 3323 [33]:
- remove all received Via header fields and then add a single Via header field with a URI of its own as described in RFC 3323 [33] subclause 5.1;
- if the Contact header field does not contain a GRUU or does not contain an isfocus media feature tag, replace the value of the URI of the Contact header field with a URI that does not dereference to the originator of the message as described in RFC 3323 [33] subclause 5.1; and
- remove any Record-Route header fields as described in RFC 3323 [33] subclause 5.1;
2) if "user" level privacy is requested as specified in RFC 3323 [33]:
- anonymize the From header field. The convention for configuring an anonymous From header field described in RFC 3323 [33] and RFC 3325 [34] should be followed; i.e. From: "Anonymous" <sip:[email protected]>;tag= xxxxxxx; and
3) if any modification of any dialog-matching headers for privacy protection reasons is done act as a transparent B2BUA as described in RFC 3323 [33] subclause 5.3.
If a Privacy header field is not received IBCF may based on local policy act as if "id", "user", "header" and "history" was received and perform privacy protection as specified in RFC 3325 [34], RFC 3323 [33] and RFC 7044 [66] with the clarifications above.
If a Privacy header field with the value "none" is received the IBCF should not protect the privacy of the identity information.
NOTE: A local policy can regard a Privacy header field with the value "none" the same as if no Privacy header field was received. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.9 Roaming architecture for voice over IMS with local breakout | The IBCF shall apply OMR as specified in 3GPP TS 29.079 [11D] and in accordance with the roaming architecture for voice over IMS with local breakout when a session is identified as a roaming architecture for voice over IMS with local breakout session.
A session can be identified as a potential roaming architecture for voice over IMS with local breakout session when:
1) a received initial INVITE request contains a Feature-Caps header field with a "+g.3gpp.trf" header field parameter, a "+g.3gpp.loopback" header field parameter or any other implementation dependent indication; or
NOTE: An implementation dependent indication can e.g. be in a URI parameter, a character string in the user part of the URI or be a port number in the URI.
2) if indicating traffic leg as specified in RFC 7549 [225] is supported and used:
a) the "iotl" SIP URI parameter with the value "visitedA-homeA" in the bottommost Route header field; or
b) the "iotl" SIP URI parameter with the value "homeA-visitedA" in the bottommost Route header field. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.10 HTTP procedures over the Ms reference point | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.10.1 General | General procedures over the Ms reference point are specified in clause V.2. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.10.2 Procedures for an IBCF acting as an entry point | When receiving an initial INVITE, re-INVITE or MESSAGE request containing one or more SIP Identity header fields, the IBCF shall determine the information (originating identity, diverting identities, contents of the Resource-Priority, Priority and Call-Info header fields) to be verified by decoding the Identity header fields containing a PASSporT SHAKEN JSON Web Token and/or a PASSporT rph JSON Web Token with an optional PASSporT sph JSON Web Token and/or a PASSporT rcd JSON Web Token. The IBCF uses the Identity header fields to:
1) build and send a verificationRequest, specified in annex V, to an AS for verification over the Ms reference point; and
2) shall upon receiving an HTTP 200 (OK) response to the above request, use:
- the verstat claim from this response to:
a) populate the "verstat" tel URI parameter associated with the originating identity and add this parameter to the verified identity in the SIP From header field or the SIP P-Asserted-Identity header field in the forwarded SIP request. Additionally, if the HTTP 200 (OK) response included verification results for the diverting identities, the IBCF shall based on local policy add the "verstat" tel URI parameter to the verified diverting identities in the History-Info header field if this field is available; and
b) based on the outcome of verification, insert the "rcd-np" Call-Info header field parameter associated with the Call-Info header field containing the RCD info in the forwarded initial INVITE request or MESSAGE request;
Editor's note: [WI: NG_RTC_Ph2, CR#6714] Specification of the "rcd-np" Call-Info header field parameter is FFS.
- the verstatPriority claim from this response to populate the Priority-Verstat header field associated with the Resource-Priority header field and with the header field value "psap-callback" of the Priority header field (if present) and include the Priority-Verstat header field in the forwarded SIP request; and
- the verifyResults from this response, if present, to store any of the PASSporT verification failure parameters shown in Table V.2.6.2-4.
Based on local policy, the IBCF may populate for each reported Identity header field verification error a Reason header field in the next provisional or final response of the INVITE or MESSAGE request, where the Reason header field protocol value is set to "STIR", as specified in RFC 9410 [294] and RFC 9366 [296], and the "cause" header field parameter contains the stored "reasonCode" value. Additionally, the IBCF may include the "ppi" header field parameter containing the failing PASSporT.
NOTE 1: Multiple Reason header fields with the protocol value set to "STIR" are not supported in the present document.
Based on local policy, the IBCF may verify that the validated claims returned in the validClaims parameter of the verification response authorize the associated SIP header field values.
NOTE 2: For sessions originating in another domain, only one of the following entities needs to be configured to verify the Identity header field for the resource priority and RCD info: the IBCF or the AS. Which functional entity inserts the Identity header field verification is subject to network configuration and local policy. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.10.10.3 Procedures for an IBCF acting as an exit point | When receiving an initial INVITE or MESSAGE request containing:
NOTE 1: As part of the border control procedures the IBCF can apply privacy procedures and in these cases this procedure is not needed.
1) a "verstat" tel URI parameter in at least one of the SIP From header field or the SIP P-Asserted-Identity header field;
2) a SIP Attestation-Info header field as defined in subclause 7.2.18;
3) a SIP Origination-Id header field as defined in subclause 7.2.19; and
4) an "rcd-np" parameter in the Call-Info header field containing the RCD info;
and if no Identity header field exists, the IBCF sends a signingRequest, specified in annex V, over the Ms reference point. When the HTTP 200 (OK) response to this request is received, the IBCF shall remove the "rcd-np" parameter from the Call-Info header field containing the RCD info and include value of the "identity" claim in an Identity header field in the forwarded SIP request.
When receiving an initial INVITE or MESSAGE request containing at least one Identity header field and a "verstat" tel URI parameter in a tel URI or a SIP URI with a user=phone parameter in one or more History-Info header field(s) or using other not specified means to determine that a diversion has occurred, then the IBCF sends a signingRequest, specified in annex V, over the Ms reference point for each of the identities to be signed. When the HTTP 200 (OK) response for any of these requests is received, the IBCF shall include the value of the "identity" claim in an Identity header field in the forwarded SIP request.
NOTE 2: As part of the border control procedures the IBCF can apply privacy procedures and in these cases this procedure is not needed.
When receiving an initial INVITE request containing the Resource-Priority header field and optionally the Priority header field with a "psap-callback" header field value or if the IBCF included the Priority header field with a "psap-callback" header field value and the Resource-Priority header field (as specified in subclause 5.10.1), the IBCF sends a signingRequest, over the Ms reference point, as specified in annex V, for the resource priority and optionally, the Priority header fields. When the HTTP 200 (OK) response to this request is received, the IBCF shall include the value of the "identity" claim in an Identity header field in the forwarded initial INVITE request.
When receiving a re-INVITE request containing the Resource-Priority header field, the IBCF sends a signingRequest, over the Ms reference point, as specified in annex V, for the resource priority. When the HTTP 200 (OK) response to this request is received, the IBCF shall include the value of the "identity" claim in an Identity header field in the forwarded re-INVITE request.
NOTE 3: For sessions terminating in another domain, only one of the following entities needs to be configured to provide an Identity header field for the resource priority: the IBCF or the AS. Which functional entity inserts the Identity header field is subject to network configuration and local policy.
If an initial INVITE request or MESSAGE request containing the Call-Info header field with RCD info is received, the RCD verification using assertion of RCD info functionality is implemented as standalone feature and required by the local policy, the IBCF sends a signingRequest, over the Ms reference point, as specified in annex V, for the RCD information and RCD URL. When the HTTP 200 (OK) response to this request is received, the IBCF shall include the value of the "identity" claim in an Identity header field in the forwarded initial INVITE request or MESSAGE request.
NOTE 4: For sessions terminating in another domain, only one of the following entities needs to be configured to provide an Identity header field for the RCD info: the IBCF or the AS. Which functional entity inserts the Identity header field is subject to network configuration and local policy. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11 Procedures at the E-CSCF | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.1 General | The PSAP may either be directly connected to the IM CN subsystem or via the PSTN. Based on regional/national requirements and network operator policy, the PSAP may be connected to the IM CN subsystem of another network.
The E-CSCF can receive URIs for a domain for which the operator running the E-CSCF is not responsible. Where RFC 3261 [26] specifies a requirement that the SIP entity has to be responsible for the domain for particular functionality to occur, the E-CSCF may ignore this restriction.
NOTE 1: The E-CSCF would normally implement this override if the P-CSCF or S-CSCF is configured to pass on URIs (e.g. Request-URI) that are outside the responsible domain of the E-CSCF, otherwise emergency calls might not be routed to a PSAP. If the P-CSCF or S-CSCF does not do this, then the override need not be applied.
The E-CSCF retrieves a PSAP URI, based on the location of the UE and the requested type of emergency service. The PSAP URI can be retrieved from LRF (see subclause 5.11.3) or from local configuration. The PSAP address will either point to a PSAP connected to the IM CN subsystem or to a PSAP connected to the PSTN.
If operator policy determines that the E-CSCF selects the PSAP and if, based on the location information contained in the INVITE request, the E-CSCF fails to select the PSAP, the E-CSCF can interrogate an external server in order to retrieve location information.
NOTE 2: The protocol used between an E-CSCF and an external server is not specified in this version of the specification.
When the E-CSCF receives an emergency request for a dialog requesting privacy or a standalone emergency transaction requesting privacy or any request or response related to a UE-originated emergency dialog requesting privacy, and if operator policy (e.g. determined by national regulatory requirements applicable to emergency services) allows requests for suppression of public user identifiers and location information per 3GPP TS 22.101 [1A], the E-CSCF:
- shall provide the privacy service role according to RFC 3323 [33] and RFC 3325 [34];
NOTE 3: The procedure above is in addition to any procedure for the application of privacy at the edge of the trust domain specified by RFC 3325 [34] and subclause 4.4.
- shall remove any location object from the message's body with Content-Type header field containing the content type application/pidf+xml. If only one message body remains in the message's body then the E-CSCF sets the Content-Type header field to the content type specified for the body; and
- shall remove the Geolocation header field (if present) and the Geolocation-Routing header field (if present);
NOTE 4: Operator policy can require retention/removal of user location information from such request or response separately from user identity, based on the national regulatory requirements.
prior to forwarding any such request to a PSAP.
NOTE 5: If the routeing functions are supported by an LRF, this information is not removed before the request is sent to the LRF.
The E-CSCF shall log all SIP requests and responses that contain a "logme" header field parameter in the SIP Session-ID header field if required by local policy.
When sending a failure response to any received request, depending on operator policy, the E-CSCF may insert a Response-Source header field with an "fe" header field parameter constructed with the URN namespace "urn:3gpp:fe", the fe-id part of the URN set to "e-cscf" and optionally an appropriate fe-param part of the URN set in accordance with subclause 7.2.17. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.2 UE originating case | The E-CSCF may forward an emergency request to a PSAP in the IM CN subsystem, a PSAP attached to another network, or a PSAP in the PSTN. If the PSAP is attached to another network, the requrest can pass IBCF(s) before entering the other network. If the PSAP is located in the PSTN, the request will pass a BGCF and a MGCF before entering the PSTN.
Upon receipt of an initial request for a dialog, or a standalone transaction, or an unknown method including a Request-URI with an emergency service URN, i.e. a service URN with a top-level service type of "sos" as specified in RFC 5031 [69], or an emergency number the E-CSCF shall:
1) if:
a) the topmost Route header field of the received SIP INVITE request contains an E-CSCF URI inserted by a P-CSCF, an AS or an IBCF;
NOTE 1: The E-CSCF is identified by two URIs, one preconfigured in the P-CSCF, AS or IBCF and one used to receive the request from EATF.
b) the Contact header field includes an instance-id feature tag containing an IMEI URN as specified in RFC 7254 [153] or an MEID URN as specified in RFC 8464 [187]. Only the IMEI shall be used for generating an instance ID for a multi-mode UE that supports both 3GPP and 3GPP2 defined radio access networks; and
c) required by the operator policy;
then:
a0) remove its own SIP URI from the topmost Route header field;
a) insert URI of the EATF to be contacted into the Route header field as the topmost entry followed by own URI to be used to receive the request from EATF;
b) insert a type 3 "orig-ioi" header field parameter in the P-Charging-Vector header field. The E-CSCF shall set the type 3 "orig-ioi" header field parameter to a value that identifies the sending network of the request. The E-CSCF shall not include the type 3 "term-ioi" header field parameter;
c) if required by national regulatory requirements applicable to emergency services, include:
- a CPC with value "emergency"; and optionally
- an OLI set to a value corresponding to the characteristics of the access used when the emergency request was initiated by the UE, i.e., an OLI that corresponds to a wireless access; and
d) route the request based on SIP routeing procedures and do not continue with the rest of the steps;
1A) remove its own SIP URI from the topmost Route header field;
1B) if the received request does not contain a P-Charging-Vector header field, insert a P-Charging-Vector header field with the "icid-value" header field parameter populated as specified in 3GPP TS 32.260 [17];
1C) if an "orig-ioi" header field parameter is received in the P-Charging-Vector header field, store the value of the received "orig-ioi" header field parameter;
NOTE 2: Any received "orig-ioi" header field parameter will be a type 2 IOI generated by an S-CSCF or passed on by an IBCF. The type 2 IOI identifies the network from which the request was sent.
1D) if operator policy determines that an LRF is to be used, forward the request to the LRF as indicated in subclause 5.11.3;
2) if the PSAP is the next hop, store the value of the "icid-value" header field parameter received in the P-Charging-Vector header field and remove the received information in the P-Charging-Vector header field, else keep the P-Charging-Vector if the next hop is an exit IBCF or a BGCF;
3) if the PSAP is the next hop remove the P-Charging-Function-Addresses header fields, if present, else keep the P-Charging-Function-Addresses header fields if the next hop is an exit IBCF or an BGCF;
4) if an IBCF or a BGCF is the next hop, delete any received "orig-ioi" header field parameter, and insert a type 2 "orig-ioi" header field parameter into the P-Charging-Vector header field. The E-CSCF shall set the type 2 "orig-ioi" header field parameter to a value that identifies the sending network. The E-CSCF shall not include the "term-ioi" header field parameter;
5) get location information as:
- geographical location information received in a PIDF location object as defined in RFC 4119 [90] and RFC 5491 [267], with the content type application/pidf+xml, as described RFC 6442 [89]; and
- location identifier as derived from the P-Access-Network-Info header field, if available.
NOTE 3: As an alternative to retrieve location information from the LRF the E-CSCF can also request location information from an external server. The address to the external server can be received in the Geolocation header field as specified in RFC 6442 [89]. The protocol used to retrieve the location information from the external server is not specified in this version of the specification.
5A) if the location is retrieved using information from the Geolocation header field, and if:
- the Geolocation-Routing header field is present, and includes a value not allowing routing of the request based on user location information;
- the Geolocation-Routing header field is present, and includes a value unknown to the E-CSCF; or
- the Geolocation-Routing header field is not present.
not use the location retrieved from the Geolocation header field when deciding where to forward the request.
6) select, based on location information and optionally type of emergency service:
a) a PSAP connected to the IM CN subsystem or another network, and add the PSAP URI to the topmost Route header field; or
NOTE 4: If the user did not request privacy or if national regulator policy applicable to emergency services does not require the user be allowed to request privacy, the E-CSCF conveys the Geolocation header field (if present), the Geolocation-Routing header field (if present), the location information in a PIDF location object (if present) and the P-Access-Network-Info header field containing the location identifier, if defined for the access type as specified in subclause 7.2A.4, to the PSAP.
b) a PSAP in the PSTN, add the BGCF URI to the topmost Route header field, add a PSAP URI in tel URI format to the Request-URI with an entry used in the PSTN/CS domain to address the PSAP and set the handling header field parameter value of the Content-Disposition header field associated with the application/pidf+xml message body (if present) to "optional";
NOTE 5: If the user did not request privacy or if national regulator policy applicable to emergency services does not require the user be allowed to request privacy, the E-CSCF conveys the Geolocation header field (if present), the Geolocation-Routing header field (if present), the location information in a PIDF location object (if present) and the P-Access-Network-Info header field containing the location identifier, if defined for the access type as specified in subclause 7.2A.4, towards the MGCF. The MGCF can translate the location information if included in INVITE (i.e. both the geographical location information in PIDF-LO and the location identifier in the P-Access-Network-Info header field) into ISUP signalling, see 3GPP TS 29.163 [11B].
NOTE 6: The way the E-CSCF determines the next hop address when the PSAP address is a tel URI is implementation dependent.
7) void;
8) if due to local policy or if the PSAP requires interconnect functionalities (e.g. PSAP address is of an IP address type other than the IP address type used in the IM CN subsystem, or the PSAP URI contains the domain name of another network), put the address of the IBCF to the topmost Route header field, in order to forward the request to the PSAP via an IBCF in the same network;
9) create a Record-Route header field containing its own SIP URI;
10) if the request is an INVITE request, save the Contact, CSeq and Record-Route header field values received in the request such that the E-CSCF is able to release the session if needed; and
11) if no P-Asserted-Identity header field is present and if required by operator policy governing the indication to PSAPs that a UE does not have sufficient credentials (e.g. determined by national regulatory requirements applicable to emergency services), insert a P-Asserted-Identity header field set to a non-dialable callback number (see ANSI/J-STD-036-B [176]);
NOTE 7: A P-Asserted-Identity header field that is present can contain a reference number used in the communication between the PSAP and LRF according to procedures in subclause 5.11.3. Such a P-Asserted-Identity header field would not be replaced with a P-Asserted-Identity header field set to a non-dialable callback number.
12) if required by national regulatory requirements applicable to emergency services, include:
- a CPC with value "emergency"; and optionally
- an OLI set to a value corresponding to the characteristics of the access used when the emergency request was initiated by the UE, i.e., an OLI that corresponds to a wireless access; and
13) route the request based on SIP routeing procedures.
NOTE 8: Depending on local operator policy, the E-CSCF has the capability to reject requests relating to specific methods in accordance with RFC 3261 [26], as an alternative to the functionality described above.
Upon receipt of an initial request for a dialog, a standalone transaction, or an unknown method, that does not include a Request-URI with an emergency service URN or an emergency number, the E-CSCF shall reject the request by sending a 403 (Forbidden) response.
When the E-CSCF receives the request containing the access-network-charging-info parameter in the P-Charging-Vector, the E-CSCF shall store the access-network-charging-info parameter from the P-Charging-Vector header field. The E-CSCF shall retain access-network-charging-info parameter in the P-Charging-Vector header field.
When the E-CSCF receives any request or response (excluding ACK requests and CANCEL requests and responses) related to a UE-originated dialog or standalone transaction, the E-CSCF may insert previously saved values into a P-Charging-Function-Addresses header field before forwarding the message.
When the E-CSCF receives any request or response related to a UE-originated dialog or standalone transaction, the E-CSCF may insert previously saved values into a P-Charging-Vector before forwarding the message. If the original request contained a P-Charging-Vector header field including an orig-IOI header field parameter, insert a type 2 "term-ioi" header field parameter in the P-Charging-Vector header field of the outgoing response. The type 2 "term-ioi" header field is set to a value that identifies the sending network of the response and the "orig-ioi" header field parameter is set to the previously received value of "orig-ioi" header field parameter. Values of "orig-ioi" and "term-ioi" header field parameters in the received response are removed.
Based on local policy the E-CSCF shall add an "fe-addr" element of the "fe-identifier" header field parameter to the P-Charging-Vector header field with its own address or identifier to an initial request.
When the E-CSCF receives any 1xx or 2xx response related to a UE-originated dialog or standalone transaction, the E-CSCF shall remove any P-Preferred-Identity header field and P-Asserted-Identity header field, and insert a P-Asserted-Identity header field with the digits that can be recognized as a valid emergency number if dialled as a tel URI representing the number, before forwarding the message.
NOTE 9: Numbers that can be recognized as valid emergency numbers if dialled by the user are specified in 3GPP TS 22.101 [1A]. The emergency numbers 112 and 911 are stored on the ME, in accordance with 3GPP TS 22.101 [1A].
When the E-CSCF receives any response related to a UE-originated dialog or standalone transaction containing a "term-ioi" header field parameter, the E-CSCF shall store the value of the received "term-ioi" header field parameter received in the P-Charging-Vector header field, if present, and remove all received "orig-ioi" and "term-ioi" header field parameters.
NOTE 10: Any received "term-ioi" header field parameter will be a type 2 IOI. The IOI identifies the sending network of the response message.
When the E-CSCF receives an INVITE request from the UE, the E-CSCF may require the periodic refreshment of the session to avoid hung states in the E-CSCF. If the E-CSCF requires the session to be refreshed, the E-CSCF shall apply the procedures described in RFC 4028 [58] clause 8.
NOTE 11: Requesting the session to be refreshed requires support by at least the UE or the PSAP or MGCF. This functionality cannot automatically be granted, i.e. at least one of the involved UAs needs to support it in order to make it work.
When the E-CSCF receives a 2xx response related to a UE-originated dialog and if:
1) the E-CSCF supports the current location discovery during the emergency call;
2) the UE indicated a Recv-Info header field with the g.3gpp.current-location-discovery info package name in the dialog of the emergency call; and
3) the UE indicated an Accept header field indicating the "application/vnd.3gpp.current-location-discovery+xml" MIME type in the dialog of the emergency call;
the E-CSCF:
1) shall include an Allow header field indicating support of the PUBLISH method in the SIP 2xx response; and
2) shall include an Allow-Events header field indicating support of the presence event package in the SIP 2xx response;
before forwarding the message. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.3 Use of an LRF | Where the network operator determines that an LRF is to be used, the E-CSCF shall route initial requests for a dialog and standalone requests that contain an emergency service URN, i.e. a service URN with a top-level service type of "sos" as specified in RFC 5031 [69], or an emergency number, to the LRF in accordance with the procedures of RFC 3261 [26].
NOTE 1: The E-CSCF is by definition responsible for emergency service URNs and is therefore allowed to change the Request-URI of requests containing emergency service URNs when a 3xx or 416 response is received.
For the outgoing request, the E-CSCF shall:
1) insert a type 3 "orig-ioi" header field parameter in the P-Charging-Vector header field. The E-CSCF shall set the type 3 "orig-ioi" header field parameter to a value that identifies the sending network of the request. The E-CSCF shall not include the type 3 "term-ioi" header field parameter; and
2) perform step 11 of subclause 5.11.2 before sending the INVITE request to the LRF.
When the E-CSCF receives any 3xx response to such a request, the E-CSCF shall select a Contact header field URI from the 3xx response according to RFC 3261 [26] and continue processing the steps given in subclause 5.11.2 with the following additions:
a) at step 6), if item a) applies, place the URI received in the selected Contact header field URI in the 3xx response in the topmost entry in the Route header field;
b) at step 6), if item b) applies, replace the original Request-URI with the URI received in the selected Contact header field URI in the 3xx response;
c) if the user did not request privacy or if national regulator policy applicable to emergency services does not require the user be allowed to request privacy, then if the selected Contact header field URI contains a P-Asserted-Identity header field encoded as a header field of the URI, replace all P-Asserted-Identity header fields in the original request with this value;
NOTE 2: Such a P-Asserted-Identity header field contains a reference number which is used in the communication between the PSAP and LRF.
d) if operator local policies allow insertion of UE location information and if the received 3xx response contains a message/external-body MIME type as specified in RFC 4483 [186] with "access-type" MIME type parameter containing "URL" and "URL" MIME type parameter containing an HTTP or HTTPS URI identifying a PIDF location object as defined in RFC 4119 [90] and RFC 5491 [267], then the E-CSCF shall insert a Geolocation header field containing this PIDF location object by reference (see RFC 6442 [89]);
e) if the location source parameter for the SIP Geolocation header field as defined in RFC 8787 [266] is supported, include a loc-src parameter in the Geolocation header field set to the domain name of the visited network; and
f) if operator policies allow forming requests from a URI and if 3xx response is received, then follow the procedures of RFC 3261 [26] subclause 19.1.5 with the following additions and clarifications:
- replacement or inclusion of any header field from the URI in the selected Contact header field is subject to operator policy; and
- if operator policy allows any LRF to provide a location by value, and the URI in the selected Contact header field contains the "Geolocation" header field, a "Geolocation-Routing" header field and a header field with hname "body" with a value, replace the entire message body with value of the header field with hname "body" in the URI in the selected Contact header field, otherwise do not perform this replacement.
If no 1xx or 2xx response to the request is received from the addressed PSAP within an operator settable timeout, or a 4xx – 5xx response is received, and additional URI values were included in the Contact header field of the response, the E-CSCF shall use these values according to RFC 3261 [26] in new requests that are otherwise generated according to the rules specified above.
If no 1xx or 2xx response to the request is received from the addressed PSAP within an operator settable timeout, or a 4xx – 5xx response is received, and all URI values included in the Contact header field of the 3xx response have been attempted, the E-CSCF shall use a default URI value configured in the E-CSCF in a new request that is otherwise generated according to the rules specified above.
If a 6xx response to the request is received, the E-CSCF acts in accordance with RFC 3261 [26].
When the E-CSCF receives any response related to the above request containing a "term-ioi" header field parameter, the E-CSCF shall store the value of the received "term-ioi" header field parameter received in the P-Charging-Vector header field, if present, and remove all received "orig-ioi" and "term-ioi" header field parameters from the forwarded response.
NOTE 3: Any received "term-ioi" header field parameter will be a type 3 IOI. The IOI identifies the sending network of the response message.
If no 3xx response to the request is received from the LRF within an operator settable timeout, the E-CSCF shall use a default URI value configured in the E-CSCF in a request that is otherwise generated according to the rules specified above. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.4 Subscriptions to E-CSCF events | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.4.1 Subscription to the event providing dialog state | When an incoming SUBSCRIBE request addressed to the E-CSCF arrives containing the Event header field with the dialog event package, the E-CSCF shall:
1) based on the local policy, check if the request was generated by a subscriber who is authorised to subscribe to the dialog state of this particular user. The authorized subscribers include:
- all the LRFs that belong to the same network operator.
If the requester is not authorised, the E-CSCF shall reject the request with an appropriate 4xx – 6xx response;
2) store the "icid-value" header field parameter received in the P-Charging-Vector header field;
3) store the "orig-ioi" header field parameter received in the P-Charging-Vector header field if present; and
NOTE: Any received "orig-ioi" header field parameter will be a type 3 IOI. The type 3 IOI identifies the service provider from which the request was sent.
4) generate a 200 (OK) response acknowledging the SUBSCRIBE request and indicating that the authorised subscription was successful as described in RFC 4235 [171]. The E-CSCF shall populate the header fields as follows:
- an Expires header field, set to either the same or a decreased value as the Expires header field in the SUBSCRIBE request; and
- a P-Charging-Vector header field containing the "orig-ioi" header field parameter, if received in the SUBSCRIBE request, a type 3 "term-ioi" header field parameter and the "icid-value" header field parameter. The E-CSCF shall set the type 3 "term-ioi" header field parameter to a value that identifies the sending network of the response, the "orig-ioi" header field parameter is set to the previously received value of the "orig-ioi" header field parameter and the "icid-value" header field parameter is set to the received value of the "icid-value" header field parameter in the request.
The E-CSCF may set the Contact header field to an identifier uniquely associated to the SUBSCRIBE request and generated within the E-CSCF, that may help the E-CSCF to correlate refreshes for the SUBSCRIBE.
Afterwards the E-CSCF shall perform the procedures for notification about dialog state as described in subclause 5.11.4.2.
When the E-CSCF receives a subscription refresh request for a dialog that was established by the UE subscribing to the dialog event package, the E-CSCF shall accept the request. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.4.2 Notification about dialog state | The E-CSCF shall send a NOTIFY request when an event pertaining to the dialog or dialogs occurs, as specified in RFC 6665 [28].
When generating NOTIFY requests, the E-CSCF shall not preclude any valid dialog event package parameters in accordance with RFC 4235 [171]. Where RFC 4235 [171] expresses an option or only a recommendation as to the generation of a NOTIFY request, it is a matter of operator policy as to whether such requests are generated.
For each NOTIFY request triggered by an event and on all dialogs which have been established due to subscription to the dialog event package, and in addition to the requirements specified in RFC 4235 [171], the E-CSCF shall:
1) set the P-Charging-Vector header field with the "icid-value" header field parameter populated as specified in 3GPP TS 32.260 [17], and a type 3 "orig-ioi" header field parameter. The E-CSCF shall set the type 3 "orig-ioi" header field parameter to a value that identifies the sending network of the request. The E-CSCF shall not include the type 3 "term-ioi" header field parameter.
2) in the body of the NOTIFY request, include one <dialog> XML element for each dialog to be reported in accordance with the subscription; and
3) for each <dialog> XML element:
- if the subscription is for all dialogs, rather than a specific dialog, then include the call-id attribute.
If the subscription is to a specific dialog (or to a specific set of dialogs), when sending a final NOTIFY request with all dialogs set to a state of "terminated", the E-CSCF shall also terminate the subscription to the dialog event package by setting the Subscription-State header field to the value of "terminated".
When the E-CSCF receives any response to the NOTIFY request, the E-CSCF shall store the value of the "term-ioi" header field parameter received in the P-Charging-Vector header field, if present.
NOTE: Any received "term-ioi" header field parameter will be a type 3 IOI. The type 3 IOI identifies the service provider from which the response was sent. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.4.3 Subscription to the presence event package | When an incoming SUBSCRIBE request addressed to the E-CSCF arrives containing the Event header field with the presence event package and a Target-Dialog header field:
1) based on the local policy, the E-CSCF shall check if the request was generated by a subscriber who is authorised to subscribe to the presence state of this particular user. The authorized subscribers include:
- all the LRFs that belong to the same network operator.
If the requester is not authorised, the E-CSCF shall reject the request with an appropriate 4xx – 6xx response;
2) the E-CSCF shall determine the dialog of the related emergency call, i.e. a confirmed dialog identified by:
a) the call identifier in the callid portion of the Target-Dialog header field; and
b) the "remote-tag" header field parameter of the Target-Dialog header field.
If such dialog does not exist, the E-CSCF shall reject the request with an appropriate 4xx – 6xx response;
3) if :
a) the UE did not indicate a Recv-Info header field with the g.3gpp.current-location-discovery info package name in the dialog of the related emergency call; or
b) the UE did not indicate an Accept header field indicating the "application/vnd.3gpp.current-location-discovery+xml" MIME type in the dialog of the related emergency call;
the E-CSCF shall reject the request with an appropriate 4xx – 6xx response;
4) the E-CSCF shall store the "icid-value" header field parameter received in the P-Charging-Vector header field;
5) the E-CSCF shall store the "orig-ioi" header field parameter received in the P-Charging-Vector header field if present; and
NOTE: Any received "orig-ioi" header field parameter will be a type 3 IOI. The type 3 IOI identifies the service provider from which the request was sent.
6) the E-CSCF shall generate a 200 (OK) response acknowledging the SUBSCRIBE request and indicating that the authorised subscription was successful as described in RFC 4235 [171]. The E-CSCF shall populate the header fields as follows:
- an Expires header field, set to either the same or a decreased value as the Expires header field in the SUBSCRIBE request; and
- a P-Charging-Vector header field containing the "orig-ioi" header field parameter, if received in the SUBSCRIBE request, a type 3 "term-ioi" header field parameter and the "icid-value" header field parameter. The E-CSCF shall set the type 3 "term-ioi" header field parameter to a value that identifies the sending network of the response, the "orig-ioi" header field parameter is set to the previously received value of the "orig-ioi" header field parameter and the "icid-value" header field parameter is set to the received value of the "icid-value" header field parameter in the request;
7) the E-CSCF shall associate the dialog of the 200 (OK) response to the SUBSCRIBE request with the dialog of the related emergency call;
8) if the Expires header field of the SUBSCRIBE request is set to zero, the E-CSCF shall perform the procedure in subclause 5.11.5.2 in the dialog of the related emergency call and shall indicate that the receiving entity is requested to send the location information once; and
9) if the Expires header field of the SUBSCRIBE request is not set to zero, the E-CSCF shall perform the procedure in subclause 5.11.5.2 in the dialog of the related emergency call and shall indicate that the receiving entity is requested to start sending the location information.
The E-CSCF may set the Contact header field to an identifier uniquely associated to the SUBSCRIBE request and generated within the E-CSCF, that may help the E-CSCF to correlate refreshes for the SUBSCRIBE.
Afterwards the E-CSCF shall perform the procedures for notification about presence event as described in subclause 5.11.4.4.
When the E-CSCF receives a subscription refresh request for the subscription associated with the initial SUBSCRIBE request, the E-CSCF shall accept the request.
When the E-CSCF receives an unsubscription request for the subscription associated with the initial SUBSCRIBE request:
1) the E-CSCF shall accept the request; and
2) if the dialog of the related emergency call still exists, the E-CSCF shall perform the procedure in subclause 5.11.5.2 in the dialog of the related emergency call and shall indicate that the receiving entity is requested to stop sending the location information. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.4.4 Notification about presence | Upon reception of a PUBLISH request in the dialog of the related emergency call as described in subclause 5.11.5.3, the E-CSCF shall send a NOTIFY request for the presence event package as specified in RFC 6665 [28]. The E-CSCF:
1) if the PUBLISH request contains a body of the "application/pidf+xml" MIME type, shall include in the NOTIFY request the body of the "application/pidf+xml" MIME type of the PUBLISH request;
2) if the PUBLISH request contains P-Access-Network-Info header field(s), shall include in the NOTIFY request the P-Access-Network-Info header field(s) of the PUBLISH request; and
3) shall set the P-Charging-Vector header field with the "icid-value" header field parameter populated as specified in 3GPP TS 32.260 [17], and a type 3 "orig-ioi" header field parameter in the NOTIFY request. The E-CSCF shall set the type 3 "orig-ioi" header field parameter to a value that identifies the sending network of the request. The E-CSCF shall not include the type 3 "term-ioi" header field parameter.
If the dialog of the related emergency call is terminated, the E-CSCF shall send a NOTIFY request for the presence event package indicating that the subscription is terminated by setting the Subscription-State header field to the "terminated" value. The E-CSCF shall set the P-Charging-Vector header field with the "icid-value" header field parameter populated as specified in 3GPP TS 32.260 [17], and a type 3 "orig-ioi" header field parameter in the NOTIFY request. The E-CSCF shall set the type 3 "orig-ioi" header field parameter to a value that identifies the sending network of the request. The E-CSCF shall not include the type 3 "term-ioi" header field parameter.
When the E-CSCF receives any response to the NOTIFY request, the E-CSCF shall store the value of the "term-ioi" header field parameter received in the P-Charging-Vector header field, if present.
NOTE: Any received "term-ioi" header field parameter will be a type 3 IOI. The type 3 IOI identifies the service provider from which the response was sent. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.5 Current location discovery during an emergency call | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.5.1 General | The UE can be requested to provide the current location information during an emergency call. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.5.2 Requesting current location informaton | If:
1) the UE indicated a Recv-Info header field with the g.3gpp.current-location-discovery info package name in the dialog of the emergency call;
2) the UE indicated an Accept header field indicating the "application/vnd.3gpp.current-location-discovery+xml" MIME type in the dialog of the emergency call; and
3) the dialog of the emergency call is a confirmed dialog;
then in order to request providing of the location information, the E-CSCF shall send an INFO request as described in RFC 6086 [25], as an in-dialog request of the dialog of the emergency call towards the UE. In the INFO request:
1) the E-CSCF shall include an Info-Package header field as described in RFC 6086 [25], containing the g.3gpp.current-location-discovery info package name; and
2) the E-CSCF shall include an request-for-current-location body as specified in subclause 7.12.2.2 in the MIME body of "application/vnd.3gpp.current-location-discovery+xml" MIME type. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.11.5.3 Receiving current location informaton | Upon receiving a PUBLISH request as described in RFC 3903 [70] as in-dialog request of the dialog of the emergency call, with Event header field containing the presence event package name, the E-CSCF shall perform the procedures described in subclause 5.11.4.4. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.12 Location Retrieval Function (LRF) | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.12.1 General | The LRF can receive URIs for a domain for which the operator running the LRF is not responsible. Where RFC 3261 [26] specifies a requirement that the SIP entity has to be responsible for the domain for particular functionality to occur, the LRF may ignore this restriction.
NOTE: The LRF would normally implement this override if the P-CSCF is configured to pass on URIs (e.g. Request-URI) that are outside the responsible domain of the LRF, otherwise emergency calls might not be routed to a PSAP. If the P-CSCF does not do this, then the override need not be applied.
The LRF shall log all SIP requests and responses that contain a "logme" header field parameter in the SIP Session-ID header field if required by local policy.
When sending a failure response to any received request, depending on operator policy, the LRF may insert a Response-Source header field with an "fe" header field parameter constructed with the URN namespace "urn:3gpp:fe", the fe-id part of the URN set to "lrf" and optionally an appropriate fe-param part of the URN set in accordance with subclause 7.2.17. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.12.2 Treatment of incoming initial requests for a dialog and standalone requests | The LRF shall respond to all received initial requests for a dialog, and to all standalone requests, as a redirect server as defined in subclause 8.3 of RFC 3261 [26] with the following additions:
1) the LRF shall generate a 300 (Multiple Choices) response to all such requests;
2) the LRF shall set the Contact header field of the response to a list (one or more) address(es) of PSAP(s), selected according to network operator policy;
NOTE 1: The mechanisms for selection of PSAP addresses are outside the scope of this specification, but can be based on a variety of input information including the value of the URN included in the Request-URI of the request, the value of the Geolocation header field and Geolocation-Routing header field received in the request, the value of the P-Access-Network-Info header field received in the request, any location known at the LRF for the requesting user as identified by the P-Access-Network-Info header field.
2A) if the location is retrieved using information from the Geolocation header field, and if:
- the Geolocation-Routing header field is present, and includes a value not allowing routing of the request based on user location information;
- the Geolocation-Routing header field is present, and includes a value unknown to the LRF; or
- the Geolocation-Routing header field is not present;
the LRF shall not use the location retrieved from the Geolocation header field when selecting PSAP(s);
2B) if the access-type field of the P-Access-Network-Info header field not containing "network-provided" parameter is set to "3GPP-NR-ProSe-L3UNR", a location is retrieved using "U2N-relay-ID" parameter of the P-Access-Network-Info header field containing the "network-provided" parameter, and the retrieved location does not match the user-provided location from the P-Access-Network-Info header field not containing the "network-provided" parameter, then the LRF shall not use the location retrieved from the P-Access-Network-Info header field not containing the "network-provided" parameter when selecting PSAP(s);
3) the LRF shall insert a P-Charging-Vector header field containing the "orig-ioi" header field parameter, if received in the request, a type 3 "term-ioi" header field parameter and the "icid-value" header field parameter. The LRF shall set the type 3 "term-ioi" header field parameter to a value that identifies the service provider from which the response is sent, the "orig-ioi" header field parameter is set to the previously received value of "orig-ioi" header field parameter and the "icid-value" header field parameter is set to the previously received value of "icid-value" header field parameter in the request;
4) optionally, generate a reference identifier and set the P-Asserted-Identity header field encoded as a header field of the URI in the Contact header field to this value in each included Contact header field URI associated with a PSAP. The LRF shall maintain state for any generated reference identifier. If the LRF uses a SIP URI (or any other permitted URI scheme other than tel URI) as the reference identifier, the LRF has the responsibility of ensuring (e.g. by configuration) that the emergency request is being routed to an IP connected PSAP. Subclause 5.12.3.1 defines a means of maintaining the state of the reference identifier. If required by operator policy governing the indication to PSAPs that a UE does not have sufficient credentials (e.g. determined by national regulatory requirements applicable to emergency services), the reference identifier shall not be equal to a non-dialable callback number used to indicate the UE does not have credentials;
NOTE 2: The reference identifier is used to correlate information requested over the Le interface (see 3GPP TS 23.167 [4B]) and is not needed if the Le interface is not used. The protocol at the Le interface is not defined in this release.
NOTE 3: The reference identifier is managed by the RDF or the LRF. If the RDF manages the reference identifier, the LRF obtains the a reference identifier from the RDF. In some regional systems, this reference identifier is the ESQK.
5) if required by operator local policies, the LRF shall include a message/external-body MIME type as specified in RFC 4483 [186] with:
a) "access-type" MIME type parameter containing "URL"; and
b) "URL" MIME type parameter containing an HTTP or HTTPS URI identifying a PIDF location object as defined in RFC 4119 [90] and RFC 5491 [267]; and
6) if required by operator local policies, the LRF shall include geographical information, encoded as header fields of the URI in a Contact header field of the 300 (Multiple Choices) response, in the following way:
a) if operator policy indicates location-by-reference is to be used:
i. a Geolocation-Routing header field with value "yes"; and
ii. a Geolocation header field that contains an HTTP URI or a HTTPS URI associated with a location-by-reference, as defined in RFC 6442 [89]; and
b) if operator policy indicates location-by-value is to be used:
i. a Geolocation-Routing header field with value "yes";
ii. Geolocation header field with value associated with the location-by-value;
iii. a header field with hname "body" and with a value that contains an escape encoded MIME body of multipart/mixed MIME type containing:
- the MIME body from the received request; and
- the geographical location information as PIDF location object in accordance with RFC 4119 [90] and RFC 5491 [267]; and
iv. a Content-Type header field with multipart/mixed MIME type.
NOTE 4: The mechanisms for selection of PSAP addresses are outside the scope of this specification. See note 1.
NOTE 5: The body of the received request can include a PIDF location object and SDP. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.12.3 Subscription and notification | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.12.3.1 Notification about dialog state | Based on operator policy, the LRF can either subscribe to all dialog information on an E-CSCF or individually subscribe to each dialog as it receives the requests.
NOTE 1: Subscription to dialog information is dependent on the use of Le interface as described in subclause 5.12.2.
In the case that the LRF is subscribing to all dialogs at the E-CSCF, the LRF shall generate a SUBSCRIBE request to the dialog state event package in accordance with RFC 6665 [28] and RFC 4235 [171]. The LRF shall include the following additional information in the SUBSCRIBE request:
a) the Request-URI set to an E-CSCF address;
NOTE 2: In this case, it is expected that the LRF will be configured with a set of E-CSCF addresses, and the LRF will subscribe to all of them.
b) no header field parameters in the Event header field;
c) an Expires header field set to 600 000 seconds; and
d) a P-Charging-Vector header field with the "icid-value" header field parameter populated as specified in 3GPP TS 32.260 [17] and a type 3 "orig-ioi" header field parameter. The type 3 "orig-ioi" header field parameter identifies the service provider from which the request is sent. The LRF shall not include the type 3 "term-ioi" header field parameter.
Upon generation of a 300 response to an incoming dialog forming request that contains a reference identifier, and in the case that the LRF is subscribing to individual dialogs at the E-CSCF, the LRF shall generate a SUBSCRIBE request to the dialog state event package in accordance with RFC 6665 [28] and RFC 4235 [171]. The LRF shall include the following additional information in the SUBSCRIBE request:
a) the Request-URI set to the value of the P-Asserted-Identity in the original request to which the response was generated;
b) a Route header field that addresses the request to the E-CSCF. How such a value is determined depends on deployment;
NOTE 3: A number of mechanisms exist for identifying the required E-CSCF, however all suffer some restrictions. It is therefore a matter of configuration at deployment time to identify the solution that works for that particular deployment. Mechanisms that exist include:
i) if there is only one E-CSCF in the network, using the address of that E-CSCF preconfigured into the system;
ii) using the last entry in the Via header field of the original request to which the 3xx response was generated. If the deployment however includes some intermediate SIP proxy or B2BUA not otherwise included in the emergency call architecture this will not provide the desired result; or
iii) using the IP address from which the original request was received to which the 3xx response was generated. The request is sent to the same port number and IP address as the 3xx response was generated. If the deployment however includes some intermediate SIP proxy or B2BUA not otherwise included in the emergency call architecture this will not provide the desired result, and additionally, if the system is set up to use port numbers in a unidirectional manner, i.e. one port number for requests and another port number for responses, it will also not operate correctly.
c) the "call-id" and "to-tag" header field parameters in the Event header field set to the values in the original request to which the 3xx response was generated. No "from-tag" header field parameter can be included as it is not known by the LRF;
d) an Expires header field set to 86400 seconds; and
e) a P-Charging-Vector header field with the "icid-value" header field parameter populated as specified in 3GPP TS 32.260 [17] and a type 3 "orig-ioi" header field parameter. The type 3 "orig-ioi" header field parameter identifies the service provider from which the request is sent. The LRF shall not include the type 3 "term-ioi" header field parameter.
In the case that the LRF is subscribing to individual dialogs at the E-CSCF, and a NOTIFY request is received indicating a state of "terminated", the LRF shall end the subscription to the dialog event package.
NOTE 4: Such NOTIFY requests will normally be accompanied by the Subscription-State header field set to the value of "terminated".
When, as a result of successful subscription to the dialog event package, the LRF receives a notification containing dialog updates, the LRF shall update its record for each dialog included in the event package information. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.12.3.2 Notification about UE location | Based on operator policy, the LRF can subscribe to UE location as it receives the requests.
Upon generation of a 300 response to an incoming dialog forming request that contains a reference identifier, the LRF shall generate a SUBSCRIBE request to the presence event package in accordance with RFC 6665 [28] and RFC 3856 [74]. The LRF shall include the following additional information in the SUBSCRIBE request:
a) the Request-URI set to an E-CSCF address;
b) a Target-Dialog header field with the callid portion and the "remote-tag" header field parameter set to the values in the original request to which the 3xx response was generated. No "local-tag" header field parameter can be included as it is not known by the LRF;
c) an Expires header field set to 86400 seconds or to 0 seconds; and
d) a P-Charging-Vector header field with the "icid-value" header field parameter populated as specified in 3GPP TS 32.260 [17] and a type 3 "orig-ioi" header field parameter. The type 3 "orig-ioi" header field parameter identifies the service provider from which the request is sent. The LRF shall not include the type 3 "term-ioi" header field parameter.
When, as a result of successful subscription to the presence event package, the LRF receives a notification containing the UE location, the LRF shall update its record for the dialog indicated in the Target-Dialog header field of the SUBSCRIBE request. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13 ISC gateway function | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.1 General | As specified in 3GPP TS 23.218 [5] border control functions may be applied between the IM CN subsystem and an application server based on operator preference. The ISC gateway function may act both as an entry point and as an exit point for a network. If it processes a SIP request received from another network it functions as an entry point (see subclause 5.13.3) and it acts as an exit point whenever it processes a SIP request sent to other network (see subclause 5.13.2).
In many cases, the ISC interface carries more than one hop of the session, e.g. the application server has applied a service to a SIP request and then returned the SIP request to the S-CSCF, or a AS acting as a third-party call controller generates multiple outgoing legs. In these cases all the requests relating to the session on all hops / legs should be configured to route through the same ISC gateway function.
NOTE 1: This is to provide for future requirements for the ISC gateway function that may need to provide correlation of the SIP transactions, and additional functionality based on that correlation.
This ISC gateway function exists on a one to one basis with its addressed AS, i.e. the URI used to address the ISC gateway function will always reach the same AS beyond the ISC gateway function.
The functionalities of the ISC gateway function are entry and exit point procedures as defined in subclause 5.13.2 and subclause 5.13.3 and additionally can include:
- network configuration hiding (as defined in subclause 5.13.4);
- application level gateway (as defined in subclause 5.13.5);
- transport plane control, i.e. QoS control (as defined in subclause 5.13.5); and
- screening of SIP signalling (as defined in subclause 5.13.6);
NOTE 2: The functionalities performed by the application level gateway are configured by the operator, and it is network specific.
The application level gateway shall log all SIP requests and responses that contain a "logme" header field parameter in the SIP Session-ID header field based on local policy. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.2 ISC gateway function as an exit point | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.2.1 Registration | There are no specific requirements for the REGISTER method, i.e. the REGISTER method is treated as for other SIP methods. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.2.2 General | This subclause applies for requests sent from the S-CSCF to the AS via the ISC gateway function.
For all SIP transactions identified:
- if priority is supported, as containing an authorised Resource-Priority header field or a temporarily authorised Resource-Priority header field, or, if such an option is supported, relating to a dialog which previously contained an authorised Resource-Priority header field, the ISC gateway function shall give priority over other transactions or dialogs. This allows special treatment of such transactions or dialogs. If priority is supported, the ISC gateway function shall adjust the priority treatment of transactions or dialogs according to the most recently received authorized Resource-Priority header field or backwards indication value.
NOTE: The special treatment can include filtering, higher priority processing, routeing, call gapping. The exact meaning of priority is not defined further in this document, but is left to national regulation and network configuration. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.2.3 Initial requests | Upon receipt of:
- an initial request for a dialog;
- a request for a standalone transaction; or
- a request for an unknown method that does not relate to an existing dialog;
the ISC gateway function shall:
1) if the request is an INVITE request, respond with a 100 (Trying) provisional response;
2) remove the topmost entry from the Route header field in accordance with RFC 3261 [26] procedures for processing Route header fields, and then add as the topmost entry the URI of the application server associated with this ISC gateway function, followed by a next entry of a URI needed to reach this ISC gateway function from the application server;
3) if the request is an INVITE request and the ISC gateway function is configured to perform application level gateway and/or transport plane control functionalities, save the Contact, CSeq and Record-Route header field values received in the request such that the ISC gateway function is able to release the session if needed;
4) If the request is a SUBSCRIBE and the ISC gateway function does not need to act as B2BUA, based on operator policy, the ISC gateway function shall determine whether or not to retain, for the related subscription, the SIP dialog state information and the duration information;
NOTE 1: The event package name can be taken into account to decide whether or not the SIP dialog state and the subscription duration information needs to be retained.
NOTE 2: The ISC gateway function needs to insert its own URI in the Record-Route header field of the initial SUBSCRIBE request and all subsequent NOTIFY requests if it decides to retain the SIP dialog state information.
5) if the request is an initial request for a dialog and local policy requires the application of ISC gateway function capabilities in subsequent requests, perform record route procedures as specified in RFC 3261 [26];
6) if the recipient of the request is understood from configured information to always send and receive private network traffic from this source, remove the P-Private-Network-Indication header field containing the domain name associated with that saved information;
7) store the values from the P-Charging-Function-Addresses header field, if present;
8) if the request is an initial request and "fe-identifier" header field parameter of P-Charging-Vector header field is applied in the operator domain;
- store the "fe-identifier" header field parameter of the P-Charging-Vector header field; and
- remove the "fe-identifier" header field parameter from the P-Charging-Vector header field;
9) remove some of the parameters from the P-Charging-Vector header field or the header field itself, depending on operator policy, if present; and
NOTE 3: An example where an ISC-GW removes the P-Charging-Vector header field is where the request is forwarded to outside the trust domain.
10) remove the P-Charging-Function-Addresses header fields, if present, prior to forwarding the message;
and forwards the request according to RFC 3261 [26].
NOTE 4: If ISC gateway function processes a request without a pre-defined route (e.g. the subscription to reg event package originated by the AS), the next-hop address can be either obtained as specified in RFC 3263 [27A] or be provisioned in the ISC gateway function.
When the ISC gateway function receives an INVITE request, the ISC gateway function may require the periodic refreshment of the session to avoid hung states in the ISC gateway function. If the ISC gateway function requires the session to be refreshed, the ISC gateway function shall apply the procedures described in RFC 4028 [58] clause 8.
NOTE 5: Requesting the session to be refreshed requires support by at least one of the UEs. This functionality cannot automatically be granted, i.e. at least one of the involved UEs needs to support it.
When the ISC gateway function receives a response to any of the requests handled in this subclause, then the ISC gateway function shall:
1) in the P-Charging-Vector header field, subject to operator policy, reinsert any parameters that were removed and stored. In addition, where the operator policy requires it, include on behalf of the supported application server a type 3 "term-ioi" header field parameter. This IOI may represent either the network of the ISC gateway function or the network providing the AS.
In responses, if "fe-identifier" header field parameter of P-Charging-Vector header field is applied in the operator domain, the ISC gateway function acting as an exit point shall:
- delete in the P-Charging-Vector header field any received "fe-identifier" header field parameter; and
- add the stored"fe-identifier" to the P-Charging-Vector header field and include its own address or identifier as an "fe-addr" element of the "fe-identifier" header field parameter of the P-Charging-Vector header.
With the exception of 305 (Use Proxy) responses, the ISC gateway function shall not recurse on 3xx responses. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.2.4 Subsequent requests | Upon receipt of a subsequent request, the ISC gateway function shall:
1) if the request is an INVITE request, respond with a 100 (Trying) provisional response;
2) if the request is a NOTIFY request with the Subscription-State header field set to "terminated" and the ISC gateway function has retained the SIP dialog state information for the associated subscription, once the NOTIFY transaction is terminated, the ISC gateway function can remove all the stored information related to the associated subscription;
3) if the request is a target refresh request and the ISC gateway function is configured to perform application level gateway and/or transport plane control functionalities, save the Contact and CSeq header field values received in the request such that the ISC gateway function is able to release the session if needed; and
4) if the subsequent request is other than a target refresh request (including requests relating to an existing dialog where the method is unknown) and the ISC gateway function is configured to perform application level gateway and/or transport plane control functionalities, save the Contact and CSeq header field values received in the request such that the ISC gateway function is able to release the session if needed;
and forwards the request, based on the topmost Route header field, in accordance with the procedures of RFC 3261 [26]. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.2.5 Call release initiated by ISC gateway function | If the ISC gateway function provides transport plane control functionality and receives an indication of a transport plane related error the ISC gateway function may:
1) generate a BYE request for the terminating side based on information saved for the related dialog; and
2) generate a BYE request for the originating side based on the information saved for the related dialog.
NOTE: Transport plane related errors can be indicated from e.g. TrGW. The protocol for indicating transport plane related errors to the ISC gateway function is out of scope of this specification.
Upon receipt of the 2xx responses for both BYE requests, the ISC gateway function shall release all information related to the dialog and the related multimedia session. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.3 ISC gateway function as an entry point | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.3.1 Registration | There are no specific requirements for the REGISTER method, i.e. the REGISTER method is treated as for other SIP methods. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.3.2 General | This subclause applies for requests sent from the AS to the S-CSCF via the ISC gateway function. Such requests come from the AS as a result of a request received from the S-CSCF and forwarded by the ISC gateway function.
For all SIP transactions identified:
- if priority is supported (NOTE), as containing an authorised Resource-Priority header field or a temporarily authorised Resource-Priority header field, or, if such an option is supported, relating to a dialog which previously contained an authorised Resource-Priority header field, the ISC gateway function shall give priority over other transactions or dialogs. This allows special treatment of such transactions or dialogs. If priority is supported, the ISC gateway function shall adjust the priority treatment of transactions or dialogs according to the most recently received authorized Resource-Priority header field or backwards indication value.
NOTE: The special treatment can include filtering, higher priority processing, routeing, call gapping. The exact meaning of priority is not defined further in this document, but is left to national regulation and network configuration. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.3.3 Initial requests | Upon receipt of:
- an initial request for a dialog;
- a request for a standalone transaction; or
- a request for an unknown method that does not relate to an existing dialog;
the ISC gateway function shall verify whether the request is arrived from a trusted domain or not. If the request arrived from an untrusted domain, then the ISC gateway function shall:
- remove all P-Charging-Vector header fields and all P-Charging-Function-Addresses header fields the request may contain.
Upon receipt of:
- an initial request for a dialog;
- a request for a standalone transaction except the REGISTER request; or
- a request for an unknown method that does not relate to an existing dialog;
the ISC gateway function shall:
1) if the request is an INVITE request, respond with a 100 (Trying) provisional response;
2) remove the topmost entry from the Route header field in accordance with RFC 3261 [26] procedures for processing Route header fields;
3) if a P-Private-Network-Indication header field is included in the request, check whether the configured information allows the receipt of private network traffic from this source. If private network traffic is allowed, the ISC gateway function shall check whether the received domain name in any included P-Private-Network-Indication header field in the request is the same as the domain name associated with that configured information. If private network traffic is not allowed, or the received domain name does not match, then the ISC gateway function shall remove the P-Private-Network-Indication header field;
4) if the initiator of the request is understood from configured information to always send and receive private network traffic from this source, insert a P-Private-Network-Indication header field containing the domain name associated with that configured information;
5) if the request is an INVITE request and the ISC gateway function is configured to perform application level gateway and/or transport plane control functionalities, then the ISC gateway function shall save the Contact, CSeq and Record-Route header field values received in the request such that the ISC gateway function is able to release the session if needed;
6) If the request is a SUBSCRIBE and the ISC gateway function does not need to act as B2BUA, based on operator policy, the ISC gateway function shall determine whether or not to retain, for the related subscription, the SIP dialog state information and the duration information; and
NOTE 1: The event package name can be taken into account to decide whether or not the SIP dialog state and the subscription duration information needs to be retained.
NOTE 2: The ISC gateway function needs to insert its own URI in the Record-Route header field of the initial SUBSCRIBE request and all subsequent NOTIFY requests if it decides to retain the SIP dialog state information.
7) if the request is an initial request for a dialog and local policy requires the application of ISC gateway function capabilities in subsequent requests, perform record route procedures as specified in RFC 3261 [26];
When the ISC gateway function receives an INVITE request, the ISC gateway function may require the periodic refreshment of the session to avoid hung states in the ISC gateway function. If the ISC gateway function requires the session to be refreshed, the ISC gateway function shall apply the procedures described in RFC 4028 [58] clause 8.
NOTE 3: Requesting the session to be refreshed requires support by at least one of the UEs. This functionality cannot automatically be granted, i.e. at least one of the involved UEs needs to support it.
When receiving an initial request and "fe-identifier" header field parameter of P-Charging-Vector header field is applied in the operator domain, the ISC gateway function acting as an entry point shall:
- add an "fe-addr" element of the "fe-identifier" header field parameter to the P-Charging-Vector header field with its own address or identifier; and
- delete in the P-Charging-Vector header field any received "fe-identifier" header field parameter.
When the ISC gateway function receives a response to an initial request (e.g. 183 or 2xx), the ISC gateway function shall:
1) store the values from the P-Charging-Function-Addresses header field, if present;
2) remove the "fe-identifier" header field parameter from the P-Charging-Vector header field, if present; and
3) remove the P-Charging-Function-Addresses header field prior to forwarding the message.
With the exception of 305 (Use Proxy) responses, the ISC gateway function shall not recurse on 3xx responses. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.3.4 Subsequent requests | Upon receipt of a subsequent request, the ISC gateway function shall:
1) if the request is an INVITE request, then respond with a 100 (Trying) provisional response;
2) if the request is a NOTIFY request with the Subscription-State header field set to "terminated" and the ISC gateway function has retained the SIP dialog state information for the associated subscription, once the NOTIFY transaction is terminated, the ISC gateway function can remove all the stored information related to the associated subscription;
3) if the request is a target refresh request and the ISC gateway function is configured to perform application level gateway and/or transport plane control functionalities, then the ISC gateway function shall save the Contact and CSeq header field values received in the request such that the ISC gateway function is able to release the session if needed;
4) if the subsequent request is other than a target refresh request (including requests relating to an existing dialog where the method is unknown) and the ISC gateway function is configured to perform application level gateway and/or transport plane control functionalities, then the ISC gateway function shall save the Contact and CSeq header field values received in the request such that the ISC gateway function is able to release the session if needed; and
5) if the subsequent request is received from outside the trust domain, then the ISC gateway function shall remove a P-Charging-Vector header field, if present;
and forwards the request, based on the topmost Route header field, in accordance with the procedures of RFC 3261 [26]. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.3.5 Call release initiated by the ISC gateway function | If the ISC gateway function provides transport plane control functionality and receives an indication of a transport plane related error the ISC gateway function may:
1) generate a BYE request for the terminating side based on information saved for the related dialog; and
2) generate a BYE request for the originating side based on the information saved for the related dialog.
NOTE: Transport plane related errors can be indicated from e.g. TrGW. The protocol for indicating transport plane related errors to the ISC gateway function is out of scope of this specification.
Upon receipt of the 2xx responses for both BYE requests, the ISC gateway function shall release all information related to the dialog and the related multimedia session. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.4 THIG functionality in the ISC gateway function | The ISC gateway function shall act according to the procedures defined for the IBCF in subclause 5.10.4 with the following exceptions:
- there are no specific requirements for the REGISTER method, i.e. the REGISTER method is treated as for other SIP methods. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.5 IMS-ALG functionality in the ISC gateway function | The ISC gateway function shall act according to the procedures defined for the IBCF in subclause 5.10.5. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 5.13.6 Screening of SIP signalling | The ISC gateway function shall act according to the procedures defined for the IBCF in subclause 5.10.6.
NOTE 1: Subclause 5.10.6 identifies a number of header fields that should not be screened. It is not expected that the ISC gateway function will see these header fields.
NOTE 2: In identifying header fields to be screened, care is needed to ensure that header fields needed by application servers later in the filter criteria chain are not removed. The ordering of the applications in the filter criteria chain might be reordered if this is a constraint that cannot be met. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6 Application usage of SDP | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.1 Procedures at the UE | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.1.1 General | The "integration of resource management and SIP" extension is hereafter in this subclause referred to as "the precondition mechanism" and is defined in RFC 3312 [30] as updated by RFC 4032 [64].
In order to authorize the media streams, the P-CSCF and S-CSCF have to be able to inspect SDP message bodies. Hence, the UE shall not encrypt SDP message bodies.
During the session establishment procedure, and during session modification procedures, SIP messages shall only contain an SDP message body if that is intended to modify the session description, or when the SDP message body is included in the message because of SIP rules described in RFC 3261 [26].
NOTE 1: A codec can have multiple payload type numbers associated with it.
In order to support accurate bandwidth calculations, the UE may include the "a=ptime" attribute for all "audio" media lines as described in RFC 4566 [39]. If a UE receives an "audio" media line with "a=ptime" specified, the UE should transmit at the specified packetization rate. If a UE receives an "audio" media line which does not have "a=ptime" specified or the UE does not support the "a=ptime" attribute, the UE should transmit at the default codec packetization rate as defined in RFC 3551 [55A]. The UE will transmit consistent with the resources available from the network.
For "video" and "audio" media types that use the RTP/RTCP and where the port number is not zero, the UE shall specify the proposed bandwidth for each media stream using the "b=" media descriptor and the "AS" bandwidth modifier in the SDP.
NOTE 2: The above is the minimum requirement for all UEs. Additional requirements can be found in other specifications.
For "video" and "audio" media types that use the RTP/RTCP and where the port number is not zero, the UE may include for each RTP payload type "a=bw-info" SDP attribute(s) (defined in clause 19 of 3GPP TS 26.114 [9B]) to indicate the additional bandwidth information. The "a=bw-info" SDP attribute line(s) shall be specified in accordance with 3GPP TS 26.114 [9B]. The value of the "a=bw-info" SDP attribute(s) may affect the assigned QoS which is defined in 3GPP TS 29.213 [13C].
For "video" and "audio" media types that utilize the RTP/RTCP, in addition to the "b=AS" parameter, the UE may specify the "b=TIAS", and "a=maxprate" parameters in accordance with RFC 3890 [152]. The value of the parameter shall be determined as described in RFC 3890 [152]. The value or absence of the "b=" parameter(s) may affect the assigned QoS which is defined in 3GPP TS 29.213 [13C].
If a UE receives a media line which contains both a=ptime and a=maxprate, the UE should use the a=maxprate value, if this attribute is supported.
If multiple codecs are specified on the media line, "a=maxprate" (or "a=ptime" if "a=maxprate" is not available or not supported) should be used to derive the packetization time used for all codecs specified on the media line. Given that not all codecs support identical ranges of packetization, the UE should ensure that the packetization derived by "a=maxprate" (or "a=ptime" if "a=maxprate" is not available or not supported) is a valid packetization time for each codec specified in the list.
If the media line in the SDP message body indicates the usage of RTP/RTCP, and if the UE is configured to request an RTCP bandwidth level for the session is different than the default RTCP bandwidth as specified in RFC 3556 [56], then in addition to the "AS" bandwidth modifier in the media-level "b=" line, the UE shall include two media-level "b=" lines, one with the "RS" bandwidth modifier and the other with the "RR" bandwidth modifier as described in RFC 3556 [56] to specify the required bandwidth allocation for RTCP. The bandwidth-value in the b=RS: and b=RR: lines may include transport overhead as described in subclause 6.1 of RFC 3890 [152].
For other media streams the "b=" media descriptor may be included. The value or absence of the "b=" parameter will affect the assigned QoS which is defined in or 3GPP 29.213 [13C].
NOTE 3: In a two-party session where both participants are active, the RTCP receiver reports are not sent, therefore, the RR bandwidth modifier will typically get the value of zero.
If an in-band DTMF codec is supported by the application associated with an audio media stream, then the UE shall include, in addition to the payload type numbers associated with the audio codecs for the media stream, for each clock rate associated with the audio codecs for the media stream, a payload type number associated with the MIME subtype "telephone-event", to indicate support of in-band DTMF as described in RFC 4733 [23].
The UE shall inspect the SDP message body contained in any SIP request or response, looking for possible indications of grouping of media streams according to RFC 3524 [54] and perform the appropriate actions for IP-CAN bearer establishment for media according to IP-CAN specific procedures (see subclause B.2.2.5 for IP-CAN implemented using GPRS, subclause L.2.2.5 for IP-CAN implemented using EPS, and subclause U.2.2.5 for IP-CAN implemented using 5GS).
In case of UE initiated resource reservation and if the UE determines resource reservation is needed, the UE shall start reserving its local resources whenever it has sufficient information about the media streams, media authorization and used codecs available.
NOTE 4: Based on this resource reservation can, in certain cases, be initiated immediately after the sending or receiving of the initial SDP offer.
In order to fulfil the QoS requirements of one or more media streams, the UE may re-use previously reserved resources. In this case the UE shall indicate as met the local preconditions related to the media stream, for which resources are re-used.
If the SDP is affected due to a rejected IP-CAN bearer or a released IP-CAN bearer then the UE shall:
1) update the session according to RFC 3264 [27B] and set the ports of the media stream(s) for which IP-CAN resource was rejected or released to zero in the new SDP offer;
2) release the session according to RFC 3261 [26];
3) cancel the session setup or the session modification according to RFC 3261 [26]; or
4) reject the session setup or the session modification according to RFC 3261 [26].
If the SDP is affected due to a modified IP-CAN bearer, and the desired QoS resources for one or more media streams are no longer available at the UE due to the modification, then the UE shall:
1) update the session according to RFC 3264 [27B] and set the ports of the media stream(s) for which IP-CAN resource was modified to zero in the new SDP offer;
2) release the session according to RFC 3261 [26];
3) cancel the session setup or the session modification according to RFC 3261 [26]; or
4) reject the session setup or the session modification according to RFC 3261 [26].
NOTE 5: The UE can use one IP address for signalling (and specify it in the Contact header field) and different IP address(es) for media (and specify it in the "c=" parameter of the SDP).
If the UE wants to transport media streams with TCP and there are no specific alternative negotiation mechanisms defined for that particular application, then the UE shall support the procedures and the SDP rules specified in RFC 4145 [83].
The UE may support being configured with a media type restriction policy using one or more of the following methods:
a) the Media_type_restriction_policy node of the EFIMSConfigData file described in 3GPP TS 31.102 [15C];
b) the Media_type_restriction_policy node of the EFIMSConfigData file described in 3GPP TS 31.103 [15B]; and
c) the Media_type_restriction_policy node of 3GPP TS 24.167 [8G].
If the UE is configured with both the Media_type_restriction_policy node of 3GPP TS 24.167 [8G] and the Media_type_restriction_policy node of the EFIMSConfigData file described in 3GPP TS 31.102 [15C] or 3GPP TS 31.103 [15B, then the Media_type_restriction_policy node of the EFIMSConfigData file shall take precedence.
NOTE 6: Precedence for files configured on both the USIM and ISIM is defined in 3GPP TS 31.103 [15B].
If the UE supports being configured with a media type restriction policy, the UE shall not include in a sent SDP message (SDP offer or SDP answer) a media stream with:
- non zero port number; and
- a media type which is restricted from inclusion in an SDP message according to the media type restriction policy.
NOTE 7: 488 (Not Acceptable Here) response is sent when all media types of all media streams of an SDP offer are restricted from inclusion in an SDP message according to the media type restriction policy. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.1.2 Handling of SDP at the originating UE | An INVITE request generated by a UE shall contain a SDP offer and at least one media description. This SDP offer shall reflect the calling user's terminal capabilities and user preferences for the session.
If the desired QoS resources for one or more media streams have not been reserved at the UE when constructing the SDP offer, the UE:
- shall indicate the related local preconditions for QoS as not met, using the segmented status type, as defined in RFC 3312 [30] and RFC 4032 [64], as well as the strength-tag value "mandatory" for the local segment and the strength-tag value either "optional" or as specified in RFC 3312 [30] and RFC 4032 [64] for the remote segment, if the UE uses the precondition mechanism (see subclause 5.1.3.1); and
- if the UE uses the precondition mechanism (see subclause 5.1.3.1), shall not request confirmation for the result of the resource reservation (as defined in RFC 3312 [30]) at the terminating UE.
NOTE 1: Previous versions of this document mandated the use of the SDP inactive attribute. This document does not prohibit specific services from using direction attributes to implement their service-specific behaviours.
If the UE uses the precondition mechanism (see subclause 5.1.3.1), and the desired QoS resources for one or more media streams are available at the UE when the SDP offer is sent, the UE shall indicate the related local preconditions as met, using the segmented status type, as defined in RFC 3312 [30] and RFC 4032 [64], as well as the strength-tag value "mandatory" for the local segment and the strength-tag value either "optional" or as specified in RFC 3312 [30] and RFC 4032 [64] for the remote segment and shall not request confirmation for the result of the resource reservation (as defined in RFC 3312 [30]) at the terminating UE.
NOTE 2: If the originating UE does not use the precondition mechanism (see subclause 5.1.3.1), it will not include any precondition information in the SDP message body.
If the UE indicated support for end-to-access-edge media security using SDES during registration, and the P-CSCF indicated support for end-to-access-edge media security using SDES during registration, then upon generating an SDP offer with an RTP based media, for each RTP based media except those for which the UE requests an end-to-end media security mechanism, the UE shall:
- offer SRTP transport protocol according to RFC 3711 [169] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP crypto attribute according to RFC 4568 [168] and the profile defined in 3GPP TS 33.328 [19C]; and
- include an SDP "a=3ge2ae:requested" attribute.
If the UE indicated support for the end-to-access-edge media security for RTP media using DTLS-SRTP and certificate fingerprints during registration, and the P-CSCF indicated support for the end-to-access-edge media security for RTP media using DTLS-SRTP and certificate fingerprints during registration, then upon generating an SDP offer with an RTP based media, for each RTP based media except those for which the UE requests an end-to-end media security mechanism, the UE shall:
- offer "UDP/TLS/RTP/SAVP" or "UDP/TLS/RTP/SAVPF" as the transport protocol according to RFC 5763 [222] and RFC 5764 [223] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP "a=3ge2ae:requested" attribute; and
- include the SDP tls-id attribute according to RFC 8842 [240].
If the UE indicated support for the end-to-access-edge media security for MSRP using TLS and certificate fingerprints during registration, and the P-CSCF indicated support for the end-to-access-edge media security for MSRP using TLS and certificate fingerprints during registration, then upon generating an SDP offer with an MSRP based media, for each MSRP based media except those for which the UE requests an end-to-end security mechanism, the UE shall:
- offer MSRP over TLS transport protocol according to RFC 4975 [178], RFC 6714 [214] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C]; and
- include the SDP "a=3ge2ae:requested" attribute.
NOTE 3: TLS client role and TLS server role are determined according to RFC 6135 [215] (referenced by RFC 6714 [214]). If the SDP answer contains the SDP setup attribute with "active" attribute value, the answerer performs the TLS client role. If the SDP answer contains the SDP setup attribute with "passive" attribute value, the offerer performs the TLS client role.
If the UE indicated support for the end-to-access-edge media security for BFCP using TLS and certificate fingerprints during registration, and the P-CSCF indicated support for the end-to-access-edge media security for BFCP using TLS and certificate fingerprints during registration, then upon generating an SDP offer with an BFCP based media, for each BFCP based media except those for which the UE requests an end-to-end security mechanism, the UE shall:
- offer BFCP over TLS transport protocol according to RFC 4583 [108] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C]; and
- include the SDP "a=3ge2ae:requested" attribute.
Unless a new TLS session is negotiated, subsequent SDP offers and answers shall not impact the previously negotiated TLS roles.
NOTE 4: RFC 4583 [108] specifies that the SDP answerer will act as the TLS server but leaves the impact of SDP renegotiation on TLS unspecified.
If the UE indicated support for the end-to-access-edge media security for UDPTL using DTLS and certificate fingerprints during registration, and the P-CSCF indicated support for the end-to-access-edge media security for UDPTL using DTLS and certificate fingerprints during registration, then upon generating an SDP offer with an UDPTL based media, for each UDPTL based media except those for which the UE requests an end-to-end security mechanism, the UE shall:
- offer UDPTL over DTLS transport protocol according to RFC 7345 [217], RFC 8842 [240] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP "a=3ge2ae:requested" attribute; and
- include the SDP tls-id attribute according to RFC 8842 [240].
If the P-CSCF did not indicate support for end-to-access-edge media security using neither DTLS-SRTP nor SDES during registration, the UE shall not include an SDP "a=3ge2ae:requested" attribute in any RTP based media in any SDP offer.
If the P-CSCF did not indicate support for the end-to-access-edge media security for MSRP using TLS and certificate fingerprints during registration, the UE shall not include an SDP "a=3ge2ae:requested" attribute in any MSRP based media in any SDP offer.
If the P-CSCF did not indicate support for the end-to-access-edge media security for BFCP using TLS and certificate fingerprints during registration, the UE shall not include an SDP "a=3ge2ae:requested" attribute in any BFCP based media in any SDP offer.
If the P-CSCF did not indicate support for the end-to-access-edge media security for UDPTL using DTLS and certificate fingerprints during registration, the UE shall not include an SDP "a=3ge2ae:requested" attribute in any UDPTL based media in any SDP offer.
The UE shall not include an SDP "a=3ge2ae:requested" attribute in any media other than RTP based, MSRP based, BFCP based and UDPTL based in any SDP offer.
Upon generating an SDP offer with an MSRP based media protected by the end-to-end media security for MSRP using TLS and KMS, the UE shall:
- offer MSRP over TLS transport protocol according to RFC 4975 [178], RFC 6714 [214] and the profile defined in 3GPP TS 33.328 [19C]; and
- include the SDP key-mgmt attribute according to RFC 4567 [167] and the profile defined in 3GPP TS 33.328 [19C];
NOTE 5: SDP fingerprint attribute is not included.
Upon receiving an SDP answer to the SDP offer with the MSRP based media protected by the end-to-end media security for MSRP using TLS and KMS, and if the MSRP based media is accepted and associated with the SDP key-mgmt attribute as described in RFC 4567 [167] and the profile defined in 3GPP TS 33.328 [19C] in the SDP answer, then the UE indicate the pre-shared key ciphersuites according to RFC 4279 [218] and the profile defined in 3GPP TS 33.328 [19C] in TLS handshake of TLS connection transporting the MSRP based media.
When the UE detects that an emergency call is being made, the UE shall not include end-to-end media security on any media in the SDP offer.
Upon generating the SDP offer for an INVITE request generated after receiving a 488 (Not Acceptable Here) response, as described in subclause 5.1.3.1, the SDP offer shall contain a subset of the allowed media types, codecs and other parameters from the SDP message bodies of all 488 (Not Acceptable Here) responses so far received for the same session establishment attempt (i.e. a set of INVITE requests used for the same session establishment). For each media line, the UE shall order the codecs in the SDP offer according to the order of the codecs in the SDP message bodies of the 488 (Not Acceptable Here) responses.
NOTE 6: The UE can attempt a session establishment through multiple networks with different policies and potentially can need to send multiple INVITE requests and receive multiple 488 (Not Acceptable Here) responses from different CSCF nodes. The UE therefore takes into account the SDP message bodies of all the 488 (Not Acceptable Here) responses received related to the same session establishment when building a new INVITE request.
Upon confirming successful local resource reservation, the UE shall create an SDP offer in which the related local preconditions are set to met, using the segmented status type, as defined in RFC 3312 [30] and RFC 4032 [64].
Upon receiving an SDP answer, which includes more than one codec per media stream, excluding the in-band DTMF codec, as described in subclause 6.1.1, the UE shall:
- send an SDP offer at the first possible time, selecting only one codec per media stream; or
- if the UE is participant in a multi-stream multiparty multimedia conference session using simulcast (indicated by the presence of "a=simulcast" SDP attribute(s) in the SDP answer, as defined in RFC 8853 [249]), apply the procedures defined in 3GPP TS 26.114 [9B] annex S.
If the UE sends an initial INVITE request that includes only an IPv6 address in the SDP offer, and receives an error response (e.g., 488 (Not Acceptable Here) with 301 Warning header field) indicating "incompatible network address format", the UE shall send an ACK as per standard SIP procedures. Subsequently, the UE may acquire an IPv4 address or use an existing IPv4 address, and send a new initial INVITE request to the same destination containing only the IPv4 address in the SDP offer. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.1.3 Handling of SDP at the terminating UE | Upon receipt of an initial SDP offer in which no precondition information is available, the terminating UE shall in the SDP answer:
- if, prior to sending the SDP answer the desired QoS resources have been reserved at the terminating UE, set the related media streams in the SDP answer to:
- active mode, if the offered media streams were not listed as inactive; or
- inactive mode, if the offered media streams were listed as inactive.
If the terminating UE had previously set one or more media streams to inactive mode and the QoS resources for those media streams are now ready, the UE shall set the media streams to active mode by applying the procedures described in RFC 4566 [39] with respect to setting the direction of media streams.
Upon sending a SDP answer to an SDP offer (which included one or more media lines which was offered with several codecs) the terminating UE shall:
- select exactly one codec per media line and indicate only the selected codec for the related media stream. In addition, the UE may indicate support of the in-band DTMF codec, as described in subclause 6.1.1; or
- if the UE is participant in a multi-stream multiparty multimedia conference session using simulcast (indicated by the presence of "a=simulcast" SDP attribute(s) in the SDP answer, as defined in RFC 8853 [249]), apply the procedures defined in 3GPP TS 26.114 [9B] annex S.
If the terminating UE does not support any of the offered codecs, or there are other parameters not acceptable to the UE, the UE shall send a 488 (Not Acceptable Here) response and shall in the response include an SDP in the message body containing the codecs and parameters supported by the UE.
Upon sending an SDP answer to an SDP offer, with the SDP answer including one or more media streams for which the originating side did indicate its local preconditions as not met, if the precondition mechanism is used by the terminating UE (see subclause 5.1.4.1), the terminating UE shall indicate its local preconditions and request the confirmation for the result of the resource reservation at the originating end point.
NOTE 1: If the terminating UE does not use the precondition mechanism (see subclause 5.1.4.1), it will ignore any precondition information received from the originating UE.
Upon receiving an initial INVITE request that includes the SDP offer containing an IP address type (in the "c=" parameter) that is not supported by the UE, the UE shall:
- if the UE is a UE performing the functions of an external attached network and
1) if the received SDP offer contains an "altc" SDP attribute indicating an alternative and supported IP address; and
2) the UE supports the "altc" SDP attribute;
select an IP address type in accordance with RFC 6947 [228]; or
- otherwise respond with a 488 (Not Acceptable Here) response including a 301 Warning header field indicating "incompatible network address format".
NOTE 2: Upon receiving an initial INVITE request that does not include an SDP offer, the UE can accept the request and include an SDP offer in the first reliable response. The SDP offer will reflect the called user's terminal capabilities and user preferences for the session.
If the UE receives an SDP offer that specifies different IP address type for media (i.e. specify it in the "c=" parameter of the SDP offer) that the UE is using for signalling, and if the UE supports both IPv4 and IPv6 addresses simultaneously, the UE shall accept the received SDP offer. Subsequently, the UE shall either acquire an IP address type or use an existing IP address type as specified in the SDP offer, and include it in the "c=" parameter in the SDP answer.
NOTE 3: Upon receiving an initial INVITE request, that includes an SDP offer containing connection addresses (in the "c=" parameter) equal to zero, the UE will select the media streams that is willing to accept for the session, reserve the QoS resources for accepted media streams, and include its valid connection address in the SDP answer.
If the UE supports the end-to-access-edge media security using SDES, upon receiving an SDP offer containing an RTP based media:
- transported using the SRTP transport protocol as defined in RFC 3711 [169];
- with an SDP crypto attribute as defined in RFC 4568 [168]; and
- with the SDP "a=3ge2ae:applied" attribute;
and if the UE accepts the RTP based media, then the UE shall generate the SDP answer with the related RTP based media:
- transported using the SRTP transport protocol according to RFC 3711 [169] and the profile defined in 3GPP TS 33.328 [19C]; and
- including an SDP crypto attribute according to RFC 4568 [168] and the profile defined in 3GPP TS 33.328 [19C].
If the UE supports the end-to-access-edge media security for RTP media using DTLS-SRTP and certificate fingerprints, upon receiving an SDP offer containing an RTP based media:
- transported using the "UDP/TLS/RTP/SAVP" or "UDP/TLS/RTP/SAVPF" as the transport protocol according to RFC 5763 [222] and RFC 5764 [223];
- with the SDP fingerprint attribute as defined in RFC 8122 [241]; and
- with the SDP "a=3ge2ae:applied" attribute;
and if the UE accepts the RTP based media, then the UE shall generate the SDP answer with the related RTP based media:
- transported using "UDP/TLS/RTP/SAVP" or "UDP/TLS/RTP/SAVPF" as the transport protocol according to RFC 5763 [222] and RFC 5764 [223] and the profile defined in 3GPP TS 33.328 [19C];
- including the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C]; and
- including the SDP tls-id attribute according to RFC 8842 [240].
If the UE supports the end-to-access-edge media security for MSRP using TLS and certificate fingerprints, upon receiving an SDP offer containing an MSRP based media:
- transported using the MSRP over TLS transport protocol as defined in RFC 4975 [178] and RFC 6714 [214];
- with the SDP fingerprint attribute as defined in RFC 8122 [241]; and
- with the SDP "a=3ge2ae:applied" attribute;
and if the UE accepts the MSRP based media, then the UE shall generate the SDP answer with the related MSRP based media:
- transported using the MSRP over TLS transport protocol according to RFC 4975 [178], RFC 6714 [214] and the profile defined in 3GPP TS 33.328 [19C]; and
- including the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C].
NOTE 4: TLS client role and TLS server role are determined according to RFC 6135 [215] (referenced by RFC 6714 [214]). If the SDP answer contains the SDP setup attribute with "active" attribute value, the answerer performs the TLS client role. If the SDP answer contains the SDP setup attribute with "passive" attribute value, the offerer performs the TLS client role.
If the UE supports the end-to-access-edge media security for BFCP using TLS and certificate fingerprints, upon receiving an SDP offer containing an BFCP based media:
- transported using the BFCP over TLS transport protocol as defined in RFC 4583 [108];
- with the SDP fingerprint attribute as defined in RFC 8122 [241]; and
- with the SDP "a=3ge2ae:applied" attribute;
and if the UE accepts the BFCP based media, then the UE shall generate the SDP answer with the related BFCP based media:
- transported using the BFCP over TLS transport protocol according to RFC 4583 [108] and the profile defined in 3GPP TS 33.328 [19C]; and
- including the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C].
Unless a new TLS session is negotiated, subsequent SDP offers and answers shall not impact the previously negotiated TLS roles.
NOTE 5: RFC 4583 [108] specifies that the SDP answerer will act as the TLS server but leaves the impact of SDP renegotiation on TLS unspecified.
If the UE supports the end-to-access-edge media security for UDPTL using DTLS and certificate fingerprints, upon receiving an SDP offer containing an UDPTL based media:
- transported using the UDPTL over DTLS transport protocol as defined in RFC 7345 [217] and RFC 8842 [240];
- with the SDP fingerprint attribute as defined in RFC 8122 [241]; and
- with the SDP "a=3ge2ae:applied" attribute;
and if the UE accepts the UDPTL based media, then the UE shall generate the SDP answer with the related UDPTL based media:
- transported using the UDPTL over DTLS transport protocol according to RFC 7345 [217], RFC 8842 [240] and the profile defined in 3GPP TS 33.328 [19C];
- including the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C]; and
- including the SDP tls-id attribute according to RFC 8842 [240].
Upon receiving an SDP offer containing an MSRP based media:
- transported using the MSRP over TLS transport protocol as defined in RFC 4975 [178] and RFC 6714 [214]; and
- with the SDP key-mgmt attribute according to RFC 4567 [167] and the profile defined in 3GPP TS 33.328 [19C];
and if the UE accepts the MSRP based media, the UE shall:
1) generate the SDP answer with the related MSRP based media:
a) transported using the MSRP over TLS transport protocol according to RFC 4975 [178], RFC 6714 [214] and the profile defined in 3GPP TS 33.328 [19C]; and
b) include the SDP key-mgmt attribute according to RFC 4567 [167] and the profile defined in 3GPP TS 33.328 [19C]; and
NOTE 6: SDP fingerprint attribute is not included.
2) indicate the pre-shared key ciphersuites according to RFC 4279 [218] and the profile defined in 3GPP TS 33.328 [19C] in TLS handshake of TLS connection transporting the MSRP based media.
If the terminating UE uses the precondition mechanism (see subclause 5.1.4.1), if the desired QoS resources for one or more media streams have not been reserved at the terminating UE when constructing the SDP offer, the terminating UE shall indicate the related local preconditions for QoS as not met, using the segmented status type, as defined in RFC 3312 [30] and RFC 4032 [64], as well as the strength-tag value "mandatory" for the local segment and the strength-tag value either "optional" or as specified in RFC 3312 [30] and RFC 4032 [64] for the remote segment.
NOTE 7: It is out of scope of this specification which media streams are to be included in the SDP offer.
If the terminating UE uses the precondition mechanism (see subclause 5.1.4.1) and if the desired QoS resources for one or more media streams are available at the terminating UE when the SDP offer is sent, the UE shall indicate the related local preconditions as met, using the segmented status type, as defined in RFC 3312 [30] and RFC 4032 [64], as well as the strength-tag value "mandatory" for the local segment and the strength-tag value either "optional" or as specified in RFC 3312 [30] and RFC 4032 [64] for the remote segment.
If the terminating UE sends an UPDATE request to remove one or more media streams negotiated in the session for which a final response to the INVITE request has not been sent yet, the terminating UE sets the ports of the media streams to be removed from the session to zero in the new SDP offer.
NOTE 8: Upon receiving an initial INVITE request with one or more media streams which the terminating UE supports and one or more media streams which the UE does not support, the UE is not expected to reject the INVITE request just because of the presence of the unsupported media stream.
NOTE 9: Previous versions of this document mandated the use of the SDP inactive attribute in the SDP offer if the desired QoS resources for one or more media streams had not been reserved at the originating UE when constructing the SDP offer unless the originating UE knew that the precondition mechanism was supported by the remote UE. The use can still occur when interoperating with devices based on earlier versions of this document. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.1.4 Session modification | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.1.4.1 General | This subclause applies after the 2xx response to the initial INVITE request has been sent or received. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.1.4.2 Generating session modification request | If the precondition mechanism is used for the session modification, the following applies:
a) if the session modification does not increase the QoS requirement of the already established media stream (e.g., all the media streams in a call hold procedure, audio stream in a call upgrade procedure), in the SDP body of the request (re-INVITE, UPDATE, or PRACK), both local and remote QoS of this media shall be indicated as met; and
b) if the session modification increases the QoS requirement of some already established media stream(s) (e.g., request of using a different audio/video codec that requires higher bandwidth), or if the session modification adds a new media stream (e.g., call upgrade), the setting of the current and desired QoS status of the modified or added media stream shall be the same as specified in subclause 6.1.2. If the network fails to modify or reserve the required resources, the UE shall send a CANCEL request to terminate the session modification. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.1.4.3 Receiving session modification request | If the precondition mechanism is used for the session modification, the settings of the current and desired QoS status shall be the same as specified in subclause 6.1.3. If the network cannot modify or reserve the required resources, the UE shall send a 580 (Precondition-Failure) response towards the UE that initiated the session modification. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.2 Procedures at the P-CSCF | The P-CSCF shall perform IMS-ALG functionality:
- when the P-CSCF needs to perform procedures for hosted NAT traversal according to Annex F; or
- when the P-CSCF needs to perform procedures for media plane security (see subclause 6.7.2.2);
- when required by the user-related policies provisioned to the P-CSCF (see subclause 5.2.1);
- when the P-CSCF needs to perform ECN procedures (see subclause 6.7.2.3);
- when the P-CSCF needs to perform procedures for OMR (see subclause 6.7.2.4);
- when the P-CSCF needs to perform P-CSCF controlled NA(P)T and NA(P)T-PT (see subclause 6.7.2.5);
- when the P-CSCF needs to perform hosted NAT procedures (see subclause 6.7.2.6);
- when the P-CSCF needs to perform ICE procedures (see subclause 6.7.2.7); or
- when the P-CSCF needs to perform transcoding procedures (see subclause 6.7.2.8).
Upon receiving an initial INVITE request that includes the SDP offer containing only an IPv6 address (in the "c=" parameter) and if the P-CSCF knows that the terminating UE supports only IPv4 addressing and does not perform the IP version interworking as described in subclause 6.7.2.5.1, the P-CSCF may, based on local policy, respond with a 488 (Not Acceptable Here) response including a 301 Warning header field indicating "incompatible network address format".
NOTE 1: How the P-CSCF determines whether the UE supports only IPv4 addressing is implementation specific.
NOTE 2: Upon receiving an initial INVITE request that does not include an SDP offer, the P-CSCF can accept the request and receive an SDP offer in the first reliable response. The SDP offer will reflect the called user's terminal capabilities and user preferences for the session.
When the P-CSCF receives any SIP request containing an SDP offer, the P-CSCF shall examine the media parameters in the received SDP offer.
If the P-CSCF finds any media parameters which are not allowed on the network by local policy or if available by bandwidth authorisation limitation information coming from the IP-CAN (e.g. via PCRF), the P-CSCF shall return a 488 (Not Acceptable Here) response containing an SDP message body. This SDP message body contains either all the media types, codecs and other SDP parameters which are allowed according to the local policy, or, based on configuration by the operator of the P-CSCF, a subset of these allowed parameters. This subset may depend on the content of the received SIP request. For each media line, the P-CSCF shall build the SDP message body in the 488 (Not Acceptable Here) response in the same manner as a UAS builds the SDP message body in a 488 (Not Acceptable Here) response as specifed in RFC 3261 [26]. The P-CSCF shall order the codecs with the most preferred codec listed first. If the SDP offer is encrypted, the P-CSCF may reject the request.
Subject to local policy, if it is not possible to generate a SDP message body (e.g. the available bandwidth is less than the bandwidth of any codec allowed by the local policy), the P-CSCF shall return a 486 (Busy here) response with a 370 Warning header field indicating "insufficient bandwidth".
When the P-CSCF receives a SIP response different from 200 (OK) response containing SDP offer, the P-CSCF shall not examine the media parameters in the received SDP offer, but the P-CSCF shall rather check the succeeding request containing the SDP answer for this offer, and if necessary (i.e. the SDP answer reduced by the UE still breaches local policy, or if available by bandwidth authorisation limitation information coming from the IP-CAN, e.g. via PCRF), the P-CSCF shall return a 488 (Not Acceptable Here) response containing the local policy allowed SDP message body. If the SDP answer is encrypted, the P-CSCF may reject the succeeding request.
When the P-CSCF receives a 200 (OK) response containing SDP offer, the P-CSCF shall examine the media parameters in the received SDP offer. If the P-CSCF finds any media parameters which are not allowed on the network by local policy or if available by bandwidth authorisation limitation information coming from the IP-CAN (e.g. via PCRF), the P-CSCF shall forward the SDP offer and on the receipt of the ACK request containing the SDP answer, the P-CSCF shall immediately terminate the session as described in subclause 5.2.8.1.2. If the SDP offer is encrypted, the P-CSCF shall forward the SDP offer and on the receipt of the ACK request containing the SDP answer, it may immediately terminate the session as described in subclause 5.2.8.1.2.
In case a device performing address and/or port number conversions is provided by a NA(P)T or NA(P)T-PT controlled by the P-CSCF, or by a hosted NAT, the P-CSCF may need to modify the media connection data in SDP message bodies according to the procedures described in annex F or subclause 6.7.2.5.
The P-CSCF shall apply the same SDP policy to the initial request or response containing an SDP message body, and throughout the complete SIP session.
The P-CSCF may inspect, if present, the "b=RS" and "b=RR" lines in order to find out the bandwidth allocation requirements for RTCP.
Subject to local policy, the P-CSCF shall prohibit the negotiation of ECN during SDP offer/answer exchanges associated with multimedia priority service by removing any ECN attribute "a=ecn-capable-rtp" from the SDP offer and shall not invoke ECN for SIP transactions associated with multimedia priority service.
Additional procedures where the P-CSCF acts as an IMS-ALG are given in subclause 6.7.2. The IMS-ALG only applies where there are specific gateway capabilities to be provided. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.3 Procedures at the S-CSCF | When the S-CSCF receives any SIP request containing an SDP offer, the S-CSCF shall examine the media parameters in the received SDP offer. If the S-CSCF finds any media parameters which are not allowed based on local policy or subscription (i.e. the information in the instances of the Core Network Service Authorization class in the service profile, described in 3GPP TS 29.228 [14]), the S-CSCF shall return a 488 (Not Acceptable Here) response containing an SDP message body. This SDP message body contains either all the media types, codecs and other SDP parameters which are allowed according to the local policy and users subscription or, based on configuration by the operator of the S-CSCF, a subset of these allowed parameters. This subset may depend on the content of the received SIP request. The S-CSCF shall build the SDP message body in the 488 (Not Acceptable Here) response in the same manner as a UAS builds the SDP message body in a 488 (Not Acceptable Here) response as specified in RFC 3261 [26]. If the SDP offer is encrypted, the S-CSCF may reject the request.
When the S-CSCF receives a SIP response different from 200 (OK) response containing SDP offer, the S-CSCF shall not examine the media parameters in the received SDP offer, but the S-CSCF shall rather check the succeeding request containing the SDP answer for this offer, and if necessary (i.e. the SDP answer reduced by the UE still breaches local policy), the S-CSCF shall return a 488 (Not Acceptable Here) response containing the local policy allowed SDP message body. If the SDP answer is encrypted, the S-CSCF may reject the succeeding request.
When the S-CSCF receives a 200 (OK) response containing an SDP offer, the S-CSCF shall examine the media parameters in the received SDP offer. If the S-CSCF finds any media parameters which are not allowed based on local policy or subscription (i.e. the information in the instances of the Core Network Service Authorization class in the service profile, described in 3GPP TS 29.228 [14]), the S-CSCF shall forward the SDP offer and on the receipt of the ACK request containing the SDP answer, the S-CSCF shall immediately terminate the session as described in subclause 5.4.5.1.2. If the SDP offer is encrypted, the S-CSCF shall forward the SDP offer and on the receipt of the ACK request containing the SDP answer, it may immediately terminate the session as described in subclause 5.4.5.1.2. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.4 Procedures at the MGCF | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.4.1 Calls originating from circuit-switched networks | The usage of SDP by the MGCF is the same as its usage by the UE, as defined in the subclause 6.1 and A.3.2, with the following exceptions:
- in an initial INVITE request generated by a MGCF, the MGCF shall indicate the current status of the local precondition;
- end-to-access edge media security is not applicable to the MGCF; and
- procedures related to the handling of the IP-CAN bearer rejection, modification or release are not applicable to the MGCF.
When sending an SDP message body, the MGCF shall not include the "i=", "u=", "e=", "p=", "r=", and "z=" descriptors in the SDP message body, and the MGCF shall ignore them if received in an SDP message body.
When the MGCF generates and sends an INVITE request for a call originating in a circuit-switched network, the MGCF shall populate the SDP with the codecs supported by the associated MGW. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.4.2 Calls terminating in circuit-switched networks | The usage of SDP by the MGCF is the same as its usage by the UE, as defined in the subclause 6.1 and A.3.2, with the following exceptions:
a) when the MGCF sends a 183 (Session Progress) response with an SDP message body, the MGCF shall only request confirmation for the result of the resource reservation (as defined in RFC 3312 [30]) at the originating end point if all of the following conditions are true:
- there are any remaining unfulfilled preconditions at the originating end point;
- the received initial INVITE request indicates support of SIP preconditions; and
- local configuration indicates support of SIP preconditions;
b) end-to-access edge media security is not applicable to the MGCF; and
c) procedures related to the handling of the IP-CAN bearer rejection, modification or release are not applicable to the MGCF.
When sending an SDP message body, the MGCF shall not include the "i=", "u=", "e=", "p=", "r=", and "z=" descriptors in the SDP message body, and the MGCF shall ignore them if received in an SDP message body.
If receiving a SIP request containing a message body with data channel media descriptors, the MGCF shall ignore them, and the MGCF shall set the data channel media port number in the data channel media descriptors as zero when sending theSIP response message to IMS network. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.4.3 Optimal Media Routeing (OMR) | If the MGCF supports OMR it shall also perform the UA procedures described in 3GPP TS 29.079 [11D]. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.4.4 Explicit congestion control support in MGCF | An MGW associated with an MGCF can support Explicit Congestion Notification (ECN) according to RFC 3168 [189], and can act as an ECN endpoint to enable ECN with a local ECN-capable terminal within a local network that properly handles ECN-marked packets.
If the MGCF receives a SDP offer containing ECN attribute "a=ecn-capable-rtp" as specified in RFC 6679 [188], and if the MGCF knows via configuration that the MGW handles ECN-marked packets properly then the MGCF, taking into account the initialisation method the MGW supports, shall return a SDP answer containing the ECN attribute "a=ecn-capable-rtp" according to RFC 6679 [188].
NOTE 1: The "leap" initialisation method is the only initialisation method the MGW supports over the Mn interface in this release.
When creating an SDP offer and if the MGCF knows via configuration that the MGW handles ECN-marked packets properly the MGCF may initiate ECN negotiation in accordance with RFC 6679 [188].
If the MGCF receives the SDP answer also containing ECN attribute "a=ecn-capable-rtp" then the MGCF will instruct the MGW to apply ECN procedures. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.5 Procedures at the MRFC | Void. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.6 Procedures at the AS | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.6.1 General | Since an AS may provide a wide range of different services, procedures for the SDP usage for an AS acting as originating UA, terminating UA or third-party call control role are dependent on the service provided to the UA and on the capabilities on the remote UA. There is no special requirements regarding the usage of the SDP, except the requirements for the SDP capabilities described in the following paragraphs and clause A.3:
1) Providing that an INVITE request generated by an AS contains an SDP message body, the AS has the capability of reflecting the originating AS's capabilities, desired QoS and precondition requirements for the session in the SDP message body.
2) When the AS sends a 183 (Session Progress) response with an SDP message body including one or more "m=" media types, it has the capability of requesting confirmation for the result of the resource reservation at the originating endpoint.
When an AS acts as a B2BUA, and it controls media resources using an MRF, it may support OMR. When the AS supports OMR, and it controls media resources using an MRF, it shall also perform the procedures described in 3GPP TS 29.079 [11D]. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.6.2 Transcoding | The AS shall send an SDP offer to the MRFC with the codecs supported by the caller and the codecs to be offered towards the callee, and the IP address and port information received from caller, in seperate media lines. When receiving an SDP answer from the MRFC, the AS shall forward the received selected codecs and IP address and port information in the callee´s media line(s) as an SDP offer towards the callee.
When the callee provides an SDP answer with selected codecs and IP address and port information, the AS shall forward this information within a new SDP offer to the MRFC. When receiving the corresponding SDP answer from the MRFC, the AS shall forward the address and port information within the caller´s media line(s) as an SDP answer towards the caller.
The codecs offered for transcoding are subject to network policy which shall be according to clause T.2. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.6.3 AS procedures to support WebRTC media optimization procedure | When an AS acts as a B2BUA, and it controls media resources using an MRF, it may support switching to transparent media for WebRTC when those media have been negotiated, as specified in annex U.2.4 of 3GPP TS 23.228 [7]. An AS that supports switching to transparent media for WebRTC shall apply the procedures in the present subclause.
NOTE 1: The AS can in addition apply OMR procedures described in 3GPP TS 29.079 [11D].
If the AS receives an SDP offer that contains any "tra-contact" SDP attribute, and the AS decides to include an MRF in the media path, the AS shall:
1) include the address information as received from the MRF in that contact line and also encapsulate the address information into each received "tra-contact" attribute, replacing previous information; and
2) transparently pass all received "tra-m-line", "tra-att", "tra-SCTP-association", "tra-media-line-number" and "tra-bw" SDP attributes.
NOTE 2: When interacting with the MRF to reserve resources and provide the information needed for media handling the AS will ask for resources suitable for the media described in the SDP offer outside the "tra-m-line", "tra-att" and "tra-bw" SDP attributes.
If an AS receives an SDP answer and the SDP answer includes "tra-m-line" media level SDP attributes, the AS shall:
1) configure the MRF to transparently pass the media described in the received "tra-m-line", "tra-att", "tra-SCTP-association", and "tra-bw" SDP attributes; and
2) transparently pass all received "tra-m-line", "tra-att", "tra-SCTP-association" and "tra-bw" SDP attributes.
NOTE 3: When interacting with MRF the AS will deactivate media plane interworking in the MRF. The AS will use the "tra-SCTP-association" SDP attributes to determine which media streams need to be multiplexed into the same SCTP association. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7 Procedures at the IMS-ALG functionality | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1 IMS-ALG in IBCF | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1.1 General | When the IBCF acts as an IMS-ALG, it makes procedures as for an originating UA and terminating UA. The IMS-ALG acts as a B2BUA. The general treatment of the SDP information between originating UA and terminating UA is described in 3GPP TS 29.162 [11A]. For the use of the IMS-ALG for specific capabilities, additional procedures are defined in subsequent subclauses.
Subject to local policy, the IBCF shall prohibit the negotiation of ECN during SDP offer/answer exchanges associated with multimedia priority service by removing any ECN attribute "a=ecn-capable-rtp" from the SDP offer and shall not invoke ECN for SIP transactions associated with multimedia priority service.
NOTE: Disabling ECN in an IBCF does not prevent a P-CSCF (IMS ALG), subject to roaming agreement, from applying ECN over the access network between a UE and the P-CSCF (IMS-ALG). |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1.2 IMS-ALG in IBCF for support of ICE | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1.2.1 General | This subclause describes procedures of an IBCF to support ICE as defined in RFC 8445 [289] and RFC 8839 [290].
If no TrGW is inserted, an IBCF may transparently pass ICE related SDP attibutes to support ICE. The remaining procedures in this subclause are only applicable if the IBCF is inserting a TrGW on the media plane.
When the IBCF with attached TrGW receives SDP candidate information from the SDP offerer the IBCF shall not forward the candidate information towards the SDP answerer. When the IBCF receives SDP candidate information from the SDP answerer the IBCF shall not forward the candidate information towards the SDP offerer. The remaining procedures in this subclause are optional.
NOTE: An IBCF that removes and/or does not provide ICE related SDP attributes (e.g. a=candidate) in the offer/answer exchange will cause the ICE procedures to be aborted and the address and port information in the m and c lines of the SDP offer will be used. If this address and port information contains the relayed candidate address of a STUN Relay server, as recommended by ICE, then an extra media relay server will be used for the session which is not necessary nor desirable.
The IBCF with attached TrGW performs separate ICE procedures towards the SDP offerer and the SDP answerer. The usage of ICE is negotiated separately with the SDP offerer and SDP answerer, and ICE may be applied independently at either side. Furthermore, the IBCF may be configured to apply ICE procedures only towards one network side, e.g. towards the IM CN subsystem it belongs to.
Since the IBCF is not located behind a NAT, it does not request the TrGW to generate keep-alive messages even when acting as a full ICE entity. The IBCF only requests the TrGW to terminate and generate STUN messages used for the candidate selection procedures.
Since the IBCF is not located behind a NAT the IBCF shall only include host candidates in SDP offers and answers generated by the IBCF. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1.2.2 IBCF full ICE procedures for UDP based streams | 6.7.1.2.2.1 General
This subclause describes the IBCF full ICE procedures for UDP based streams.
6.7.1.2.2.2 IBCF receiving SDP offer
When the IBCF receives an SDP offer including ICE candidate information, the IBCF shall send the candidate information for each UDP based stream received in the SDP offer towards the TrGW. The IBCF will request the TrGW to reserve media- and STUN resources towards the SDP offerer, based on the candidate information, in order to allow the TrGW to perform the necessary connectivity checks per the ICE procedures.
If the SDP offerer is acting as an ICE controller entity the IBCF shall act as an ICE controlled entity in the direction towards the SDP offerer. If the SDP offerer is acting as an ICE controlled entity the IBCF shall act as an ICE controller entity in the direction towards the SDP offerer.
6.7.1.2.2.3 IBCF sending SDP offer
Prior to sending an SDP offer, the IBCF may choose to apply related ICE procedues, e.g. if it expects to interact with terminals applying procedures as described in subclause K.5.2, and if both the IBCF and TrGW also support ICE procedures. To invoke these ICE procedures, the IBCF will request the TrGW to reserve media- and STUN resources towards the SDP answerer for each UDP based media stream and include a host candidate attribute for each UDP based stream in the SDP offer, providing the reserved address and port at the TrGW as destination.
The IBCF shall always act as an ICE controller entity towards the SDP answerer.
NOTE: The host candidate address included by the IBCF in the generated SDP offer matches the c- and m line information for the associcated UDP stream in the SDP offer.
6.7.1.2.2.4 IBCF receiving SDP answer
When the IBCF receives an SDP answer including ICE candidate information, the IBCF will send the candidate information for each UDP based stream received in the SDP answer towards the TrGW.
The IBCF will request the TrGW to perform ICE candidate selection procedures towards the SDP answerer. The IBCF will request the TrGW to inform the IBCF, for each UDP stream, which candidate pair has been selected towards the SDP answerer, once the candidate selection procedure towards the SDP answerer has finished.
If the TrGW indicates to the IBCF that, for at least one UDP stream, the selected candidate pair does not match the c- and m- line address information for the associated UDP stream, exchanged between the IBCF and the SDP answerer, and the IBCF acts an ICE controller entity towards the SDP answerer, the IBCF shall send a new offer towards the SDP answerer in order to allign the c- and m- lines address information with the chosen candidate pair for the associated UDP stream.
6.7.1.2.2.5 IBCF sending SDP answer
When the IBCF generates an SDP answer for an offer that included ICE candidate information, the IBCF will request the TrGW to reserve media- and STUN resources towards the SDP offerer for each UDP based media stream and include an SDP host candidate attribute for each UDP based stream in the SDP answer, providing the reserved address and port at the TrGW as destination.
The IBCF shall in the generated SDP answer include host candidate information which matches the c- and m line information for the associated UDP stream in the SDP answer.
The IBCF will request the TrGW to perform ICE candidate selection procedures towards the SDP offerer. The IBCF will request the TrGW to inform the IBCF, for each UDP stream, which candidate pair has been selected towards the SDP offerer, once the candidate selection procedure towards the SDP answerer has finished.
If the TrGW indicates to the IBCF that the selected candidate pair towards the SDP offerer does not match the c- and m- line address information for the associated UDP stream, exchanged between the IBCF and the SDP offerer, and the IBCF acts an ICE controller entity towards the SDP offerer, the IBCF shall send an offer towards the SDP offerer (which will now act as an SDP answerer) in order to allign the c- and m- line address information with the chosen candidate pair for the associated UDP stream. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1.2.3 IBCF ICE lite procedures for UDP based streams | When the IBCF is using ICE lite procedures for UDP based streams, the IBCF procedures are identical as described in subclause 6.7.1.2.2, with the following exceptions:
- The IBCF always acts as an ICE controlled entity towards the SDP offerer and towards the SDP answerer, and;
- The IBCF requests the TrGW to perform ICE lite candidate selection procedures, as defined in ICE |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1.2.4 ICE procedures for TCP based streams | 6.7.1.2.4.1 General
The IBCF shall terminate ICE procedures for TCP based streams. Instead the IBCF will use the mechanism defined in RFC 4145 [83] for establishing TCP based streams, as defined in RFC 6544 [131].
An entity that supports ICE continues the ICE procedures for UDP based streams, even if no candidates are provided for TCP based streams.
NOTE: The IBCF ICE procedures for TCP based streams are identical no matter whether the IBCF uses full ICE- or ICE lite- procedures for UDP based streams.
6.7.1.2.4.2 IBCF receiving SDP offer
When the IBCF receives an SDP offer, the IBCF shall ignore the candidate attributes for TCP based streams. The IBCF shall not send the candidate information for TCP based streams towards the TrGW.
6.7.1.2.4.3 IBCF sending SDP offer
When the IBCF generates an SDP offer the IBCF shall include an "actpass" setup attribute, as defined in RFC 4145 [83], for each TCP based stream, which will cause the SDP answerer to initiate the TCP connections towards the TrGW. The IBCF shall not include any candidate attributes for TCP based streams in the SDP offer.
6.7.1.2.4.4 IBCF receiving SDP answer
Since the IBCF does not include candidates in the SDP offer towards the SDP answerer, there are no ICE specific procedures when the IBCF receives an SDP answer.
NOTE: If the SDP answer contains candidate attributes for TCP based streams, the IBCF simply discards the candidate attributes.
6.7.1.2.4.5 IBCF sending SDP answer
When the IBCF generates an SDP answer the IBCF shall include a "passive" setup attribute, as defined in RFC 4145 [83], for each TCP based stream, which will cause the SDP offerer to initiate the TCP connections towards the TrGW. The IBCF shall not include any candidate attributes for TCP based streams in the SDP answer. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1.3 IMS-ALG in IBCF for transcoding | Before forwarding the SDP offer to the answerer, the IBCF may add to the selected media one or more codecs to the codec list contained in the SDP offer. The codecs added to the SDP offer are based on local policy and shall be in accordance with the requirements of clause T.2.
NOTE 1: The local policy can be based on supported codecs in the terminating network.
Upon receipt of an SDP answer, the IBCF shall inspect the list of the returned codecs and proceed as follows:
- if the list contains at least one of the codecs belonging to the original SDP offer, the IBCF shall not invoke the transcoding function; and
- if the list contains none of the codecs belonging to the original SDP offer, the IBCF shall select one of the returned codecs introduced in the answer and invoke the transcoding function. In order to perform the transcoding the IBCF shall select one of the codecs originally offered and set to a non-zero port value the related media stream in the answer sent to the offerer.
NOTE 2: The protocol used between IBCF and TrGW to allow the transport plane media trascoding control is out of scope of this specification. The codec selected by the answerer and the one selected by the IBCF and sent to the offerer can be used to instruct the TrGW for the transcoding purposes.
The IBCF shall remove from the SDP the codecs added to the original SDP offer before forwarding the SDP answer to the offerer.
NOTE 3: In accordance with normal SDP procedure the transcoding IBCF informs the answerer of the properties of the chosen codecs (IP-address and ports). |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1.4 IMS-ALG in IBCF for NA(P)T and NA(P)T-PT controlled by the IBCF | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1.4.1 General | This subclause describes the IBCF procedures for supporting the scenario where IP address and/or port conversions occur at the TrGW level in the media path between the UE and the backbone. Two types of address conversions are covered:
- IP version interworking (NA(P)T-PT); and
- IP address/port translation (NA(P)T).
When the IBCF performs procedures for IBCF controlled NA(P)T and NA(P)T-PT, the IBCF shall modify the IP address(es) and port numbers (in case of NA(P)T) in SDP offers and answers, based on the IP address(es) and port number(s) received from the TrGW, as described in subclause 6.7.2.1.
For terminating sessions the IBCF may towards a UE performing the functions of an external attached network indicate in the SDP offer alternate IP address versions (IPv4 and IPv6) by inserting two "altc" attributes as defined in RFC 6947 [228]. The order of setting the two IP addresses in the two "altc" SDP attributes shall be based on local policy. The insertion of the "altc" attributes is independent of their presence in the received SDP offer.
NOTE 1: The insertion of alternate IP versions allows avoiding the rejection of the SDP offer because of incompatible network address formats and when the request terminates in a corporate network enables the corporate network to avoid IP version interworking.
NOTE 2: The handling of alternative IP addresses between the IMS-ALG and the TrGW is defined in 3GPP TS 29.162 [11A].
If the IBCF sends an initial INVITE request that includes only an IPv6 address in the SDP offer, and receives a 488 (Not Acceptable Here) response with 301 Warning header field indicating "incompatible network address format", the IBCF shall send an ACK as per standard SIP procedures. Subsequently, based on operator policy, the IBCF may, by performing the IP version interworking, acquire an IPv4 address or use an existing IPv4 address, and send a new initial INVITE request to the same destination containing only the IPv4 address in the SDP offer. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.1.5 IMS-ALG procedure in IBCF to support WebRTC media optimization procedure | The IMS-ALG in the IBCF may support switching to transparent media for WebRTC when those media have been negotiated, as specified in annex U.2.4 of 3GPP TS 23.228 [7]. An IMS-ALG that supports switching to transparent media for WebRTC shall apply the procedures in the present subclause.
NOTE 1: The IMS-ALG can in addition apply OMR procedures described in 3GPP TS 29.079 [11D].
If the IMS-ALG receives an SDP offer that contains any "tra-contact" SDP attribute, and the IMS-ALG decides to include a TrGw in the media path, the IMS-ALG shall:
1) include the address information as received from the TrGW in that contact line and also encapsulate the address information into each received "tra-contact" attribute, replacing previous information; and
2) transparently pass all received "tra-m-line", "tra-att", "tra-SCTP-association", "tra-media-line-number" and "tra-bw" SDP attributes.
NOTE 2: When interacting with the TrGW to reserve resources and provide the information needed for media handling the IMS-ALG will ask for resources suitable for the media described in the SDP offer outside the "tra-m-line", "tra-att" and "tra-bw" SDP attributes. The details of the interaction between the IMS-ALG and the TrGW are out of scope of this document.
If an IMS-ALG receives an SDP answer and the SDP answer includes "tra-m-line" media level SDP attributes, the IMS-ALG shall:
1) configure the TrGW to transparently pass the media described in the received "tra-m-line", "tra-att", "tra-SCTP-association", and "tra-bw" SDP attributes; and
2) transparently pass all received "tra-m-line", "tra-att", "tra-SCTP-association" and "tra-bw" SDP attributes.
NOTE 3: When interacting with TrGW the IMS-AGW will deactivate media plane interworking in the TrGW. The details of this interaction are out of scope of this document. The IMS-AGW will use the "tra-SCTP-association" SDP attributes to determine which media streams need to be multiplexed into the same SCTP association. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.2 IMS-ALG in P-CSCF | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.2.1 General | This subclause specifies the general procedures for the support of SDP in IMS-ALG within the P-CSCF. For the use of the IMS-ALG for specific capabilities, additional procedures are defined in subsequent subclauses.
When the IMS-ALG receives an SDP offer, it shall create a new SDP offer, based the contents of the received SDP offer, modified according to procedures and policies associated with specific capabilities that the IMS-ALG is used for, according to capabilities supported by the IMS-AGW, and to provide the IP address and port information received by the IMS-AGW.
When the IMS-ALG receives an SDP answer, it shall create a new SDP answer, to respond to the originally received SDP offer, modified according to the same procedures and policies that were used to modify the SDP offer.
The P-CSCF may receive multiple provisional responses with an SDP answer due to forking of a request before the first final answer is received. For each SDP answer received in such subsequent provisional responses, the P-CSCF shall apply the procedure in this subclause.
After the session is established, it is possible for both ends of the session to change the media connection data for the session. When the P-CSCF receives a SDP offer/answer where port number(s) or IP address(es) is/are included, there are three different possibilities:
- IP address(es) or/and port number(s) have been added;
- IP address(es) and port number(s) have been reassigned to the end points; or
NOTE 1: If necessary, the P-CSCF will request the IMS-AGW access gateway to release the resources related to the previously assigned IP address(es) and port number(s).
- no change has been made to the IP address(es) and port number(s).
NOTE 2: In the particular case of RTP flows, port conversions also apply to the associated RTCP flows. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.2.2 IMS-ALG in P-CSCF for media plane security | When the P-CSCF acts as an IMS-ALG, it acts as a B2BUA and modifies the SDP as described as described in 3GPP TS 23.334 [7F].
If the P-CSCF indicated support for end-to-access-edge media security using SDES during registration:
1) upon receiving an SDP offer from the served UE containing an end-to-access-edge protected RTP based media, i.e. a RTP media stream:
- transported using the SRTP transport protocol as defined in RFC 3711 [169];
- with an SDP crypto attribute as defined in RFC 4568 [168]; and
- with the SDP "a=3ge2ae:requested" attribute;
the P-CSCF shall invoke IMS-ALG procedures, will act as defined in 3GPP TS 23.334 [7F] as far as SDP and SRTP is concerned, and shall:
- if the SDP offer contains a Transport Protocol Capability SDP attribute (see RFC 5939 [137]) offering:
a) "RTP/SAVPF" transport, e.g. "a=tcap:x RTP/SAVPF", replace this transport with "RTP/AVPF" within that attribute; and
b) "RTP/SAVP" transport, e.g. "a=tcap:x RTP/SAVP", replace this transport with "RTP/AVP" within that attribute; and
- strip the SDP "a=3ge2ae:requested" attribute and the SDP crypto attribute from the end-to-access-edge protected RTP based media of the received SDP offer; and
2) upon sending an SDP answer to the SDP offer from the served UE, for each end-to-access-edge protected RTP based media of the SDP offer from the served UE which is accepted in the SDP answer, the P-CSCF will act as defined in 3GPP TS 23.334 [7F] as far as SDP and SRTP is concerned and shall:
- indicate the SRTP transport protocol according to RFC 3711 [169] and the profile defined in 3GPP TS 33.328 [19C]; and
- include a SDP crypto attribute according to RFC 4568 [168] and the profile defined in 3GPP TS 33.328 [19C].
If the served UE indicated support for end-to-access-edge media security using SDES, during registration, and the P-CSCF indicated support for end-to-access-edge 2ae-media security using SDES during registration:
1) upon receiving an SDP offer from remote user with an RTP based media, for each end-to-access-edge protected RTP based media, i.e. a RTP based media except those for which the result of the SDP offer / answer exchange results in the application of an end-to-end media security mechanism, the P-CSCF shall invoke IMS-ALG procedures, will act as defined in 3GPP TS 23.334 [7F] as far as SDP and RTP is concerned, and shall:
- remove any SDP crypto attribute and any "a=acap:x crypto" SDP attribute (see RFC 5939 [137]);
- if the SDP offer contains any potential configuration(s) using "RTP/SAVPF" transport or "RTP/SAVP" transport, as offered in corresponding Transport Protocol Capability SDP attribute(s) (see RFC 5939 [137]), (e.g. "a=tcap:x RTP/AVPF a=pcfg:y t=x"), remove those potential configuration(s);
NOTE: Keeping the related "RTP/SAVPF" transport or "RTP/SAVP" transport within a Transport Protocol Capability SDP attribute that also contains other transports avoids a potential need to renumber other transports and adjust other potential configurations in the SDP offer and the actual configuration in the SDP answer accordingly.
- if the SDP offer contains a Transport Protocol Capability SDP attribute (see RFC 5939 [137]) offering:
a) "RTP/AVPF" transport (e.g. "a=tcap:x RTP/AVPF"), replace this transport with "RTP/SAVPF" within that attribute; and
b) "RTP/AVP" transport (e.g. "a=tcap:x RTP/AVP"), replace this transport with "RTP/SAVP" within that attribute;
- if the SDP offer contains any potential configuration(s) with delete-attribute parameter(s) (see RFC 5939 [137]), (e.g. "a=pcfg:1 a=-sm:1"), remove those potential configuration(s);
- offer SRTP transport protocol according to RFC 3711 [169] and the profile defined in 3GPP TS 33.328 [19C];
- include a SDP crypto attribute according to RFC 4568 [168] and the profile defined in 3GPP TS 33.328 [19C]; and
- include a SDP "a=3ge2ae:applied" attribute; and
2) upon receiving an SDP answer to the SDP offer from remote user, for each accepted end-to-access-edge protected RTP based media, the P-CSCF will act as defined in 3GPP TS 23.334 [7F] as far as SDP and RTP is concerned, and shall remove the SDP crypto attribute.
If the P-CSCF indicated support for the end-to-access-edge media security for RTP media using DTLS-SRTP and certificate fingerprints during registration:
1) upon receiving an SDP offer from the served UE containing an end-to-access-edge protected RTP based media, i.e. an RTP based media:
- transported using "UDP/TLS/RTP/SAVP" or "UDP/TLS/RTP/SAVPF" as the transport protocol according to RFC 5763 [222] and RFC 5764 [223];
- with the SDP fingerprint attribute as defined in RFC 8122 [241];
- with the SDP "a=3ge2ae:requested" attribute; and
- with the SDP tls-id attribute as defined in RFC 8842 [240];
the P-CSCF shall invoke IMS-ALG procedures, will act as defined in 3GPP TS 23.334 [7F] as far as SDP and "RTP/AVP" or "RTP/AVPF" over UDP is concerned, and shall strip the SDP "a=3ge2ae:requested" attribute, the SDP fingerprint attribute and the SDP tls-id attribute from the RTP based media of the received SDP offer; and
2) upon sending an SDP answer to the SDP offer from the served UE, for each end-to-access-edge protected RTP based media of the SDP offer from the served UE that is accepted in the SDP answer, the P-CSCF will act as defined in 3GPP TS 23.334 [7F] as far as SDP and "RTP/AVP" or "RTP/AVPF" over UDP is concerned and shall:
- indicate the "UDP/TLS/RTP/SAVP" or "UDP/TLS/RTP/SAVPF" as the transport protocol according to RFC 5763 [222], RFC 5764 [223] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C]; and
- include the SDP tls-id attribute as defined in RFC 8842 [240].
If the served UE indicated support for the end-to-access-edge media security for RTP media using DTLS-SRTP and certificate fingerprints during registration, and the P-CSCF indicated support for the end-to-access-edge media security for RTP media using DTLS-SRTP and certificate fingerprints during registration:
1) upon receiving an SDP offer from remote UE with an RTP based media, for each end-to-access-edge protected RTP based media, i.e. an RTP based media except those for which the result of the SDP offer / answer exchange results in the application of an end-to-end security mechanism, the P-CSCF shall invoke IMS-ALG procedures, will act as defined in 3GPP TS 23.334 [7F] as far as SDP and "RTP/AVP" or "RTP/AVPF" over UDP is concerned, and shall:
- remove any SDP fingerprint attribute;
- remove any SDP tls-id attribute;
- offer "UDP/TLS/RTP/SAVP" or "UDP/TLS/RTP/SAVPF" as the transport protocol according to RFC 5763 [222], RFC 5764 [223] and the profile defined in 3GPP TS 33.328 [19C];
- if the SDP offer contains any potential configuration(s) with delete-attribute parameter(s) (see RFC 5939 [137]), (e.g. "a=pcfg:1 a=-sm:1"), remove those potential configuration(s);
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP "a=3ge2ae:applied" attribute; and
- include the SDP tls-id attribute as defined in RFC 8842 [240]; and
2) upon receiving an SDP answer to the SDP offer from remote user, for each accepted end-to-access-edge protected RTP based media, the P-CSCF will act as defined in 3GPP TS 23.334 [7F] as far as SDP and "RTP/AVP" or "RTP/AVPF" over UDP is concerned, and shall remove the SDP fingerprint attribute and SDP tls-id attribute.
If the P-CSCF indicated support for the end-to-access-edge media security for MSRP using TLS and certificate fingerprints during registration:
1) upon receiving an SDP offer from the served UE containing an end-to-access-edge protected MSRP based media, i.e. an MSRP based media:
- transported using the MSRP over TLS transport protocol as defined in RFC 4975 [178] and RFC 6714 [214];
- with the SDP fingerprint attribute as defined in RFC 8122 [241]; and
- with the SDP "a=3ge2ae:requested" attribute;
the P-CSCF shall invoke IMS-ALG procedures, will act as defined in 3GPP TS 23.334 [7F] as far as SDP and MSRP is concerned, and shall strip the SDP "a=3ge2ae:requested" attribute and the SDP fingerprint attribute from the end-to-access-edge protected MSRP based media of the received SDP offer; and
2) upon sending an SDP answer to the SDP offer from the served UE, for each end-to-access-edge protected MSRP based media of the SDP offer from the served UE which is accepted in the SDP answer, the P-CSCF will act as defined in 3GPP TS 23.334 [7F] as far as SDP and MSRP is concerned and shall:
- indicate the MSRP over TLS transport protocol according to RFC 4975 [178], RFC 6714 [214] and the profile defined in 3GPP TS 33.328 [19C]; and
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C].
If the served UE indicated support for the end-to-access-edge media security for MSRP using TLS and certificate fingerprints during registration, and the P-CSCF indicated support for the end-to-access-edge media security for MSRP using TLS and certificate fingerprints during registration:
1) upon receiving an SDP offer from remote user with an MSRP based media, for each end-to-access-edge protected MSRP based media, i.e. an MSRP based media except those for which the result of the SDP offer / answer exchange results in the application of an end-to-end security mechanism, the P-CSCF shall invoke IMS-ALG procedures, will act as defined in 3GPP TS 23.334 [7F] as far as SDP and MSRP is concerned, and shall:
- remove any SDP fingerprint attribute;
- offer MSRP over TLS transport protocol according to RFC 4975 [178], RFC 6714 [214] and the profile defined in 3GPP TS 33.328 [19C];
- if the SDP offer contains any potential configuration(s) with delete-attribute parameter(s) (see RFC 5939 [137]), (e.g. "a=pcfg:1 a=-sm:1"), remove those potential configuration(s);
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C]; and
- include the SDP "a=3ge2ae:applied" attribute; and
2) upon receiving an SDP answer to the SDP offer from remote user, for each accepted end-to-access-edge protected MSRP based media, the P-CSCF will act as defined in 3GPP TS 23.334 [7F] as far as SDP and MSRP is concerned, and shall remove the SDP fingerprint attribute.
If the P-CSCF indicated support for the end-to-access-edge media security for BFCP using TLS and certificate fingerprints during registration:
1) upon receiving an SDP offer from the served UE containing an end-to-access-edge protected BFCP based media, i.e. a BFCP based media:
- transported using the BFCP over TLS transport protocol as defined in RFC 4583 [108];
- with the SDP fingerprint attribute as defined in RFC 8122 [241]; and
- with the SDP "a=3ge2ae:requested" attribute;
the P-CSCF shall invoke IMS-ALG procedures, will act as defined in 3GPP TS 23.334 [7F] as far as SDP and BFCP is concerned, and shall strip the SDP "a=3ge2ae:requested" attribute and the SDP fingerprint attribute from the BFCP based media of the received SDP offer; and
2) upon sending an SDP answer to the SDP offer from the served UE, for each end-to-access-edge protected BFCP based media of the SDP offer from the served UE which is accepted in the SDP answer, the P-CSCF will act as defined in 3GPP TS 23.334 [7F] as far as SDP and BFCP is concerned and shall:
- indicate the BFCP over TLS transport protocol according to RFC 4583 [108] and the profile defined in 3GPP TS 33.328 [19C]; and
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C].
If the served UE indicated support for the end-to-access-edge media security for BFCP using TLS and certificate fingerprints during registration, and the P-CSCF indicated support for the end-to-access-edge media security for BFCP using TLS and certificate fingerprints during registration:
1) upon receiving an SDP offer from remote UE with an BFCP based media, for each end-to-access-edge protected BFCP based media, i.e. a BFCP based media except those for which the result of the SDP offer / answer exchange results in the application of an end-to-end security mechanism, the P-CSCF shall invoke IMS-ALG procedures, will act as defined in 3GPP TS 23.334 [7F] as far as SDP and BFCP is concerned, and shall:
- remove any SDP fingerprint attribute;
- offer BFCP over TLS transport protocol according to RFC 4583 [108] and the profile defined in 3GPP TS 33.328 [19C];
- if the SDP offer contains any potential configuration(s) with delete-attribute parameter(s) (see RFC 5939 [137]), (e.g. "a=pcfg:1 a=-sm:1"), remove those potential configuration(s);
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C]; and
- include the SDP "a=3ge2ae:applied" attribute; and
2) upon receiving an SDP answer to the SDP offer from remote user, for each accepted end-to-access-edge protected BFCP based media, the P-CSCF will act as defined in 3GPP TS 23.334 [7F] as far as SDP and BFCP is concerned, and shall remove the SDP fingerprint attribute.
If the P-CSCF indicated support for the end-to-access-edge media security for UDPTL over DTLS and certificate fingerprints during registration:
1) upon receiving an SDP offer from the served UE containing an end-to-access-edge protected UDPTL based media, i.e. a UDPTL based media:
- transported using the UDPTL over DTLS transport protocol as defined in RFC 7345 [217] and RFC 8842 [240];
- with the SDP fingerprint attribute as defined in RFC 8122 [241];
- with the SDP "a=3ge2ae:requested" attribute; and
- with the SDP tls-id attribute as defined in RFC 8842 [240];
the P-CSCF shall invoke IMS-ALG procedures, will act as defined in 3GPP TS 23.334 [7F] as far as SDP and UDPTL is concerned, and shall strip the SDP "a=3ge2ae:requested" attribute and the SDP fingerprint attribute and the SDP tls-id attribute from the UDPTL based media of the received SDP offer; and
2) upon sending an SDP answer to the SDP offer from the served UE, for each end-to-access-edge protected UDPTL based media of the SDP offer from the served UE which is accepted in the SDP answer, the P-CSCF will act as defined in 3GPP TS 23.334 [7F] as far as SDP and UDPTL is concerned and shall:
- indicate the UDPTL over DTLS transport protocol according to RFC 7345 [217], RFC 8842 [240] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C]; and
- include the SDP tls-id attribute as defined in RFC 8842 [240].
If the served UE indicated support for the end-to-access-edge media security for UDPTL using DTLS and certificate fingerprints during registration, and the P-CSCF indicated support for the end-to-access-edge media security for UDPTL using DTLS and certificate fingerprints during registration:
1) upon receiving an SDP offer from remote UE with an UDPTL based media, for each end-to-access-edge protected UDPTL based media, i.e. a UDPTL based media except those for which the result of the SDP offer / answer exchange results in the application of an end-to-end security mechanism, the P-CSCF shall invoke IMS-ALG procedures, will act as defined in 3GPP TS 23.334 [7F] as far as SDP and UDPTL is concerned, and shall:
- remove any SDP fingerprint attribute;
- remove any SDP tls-id attribute;
- offer UDPTL over DTLS transport protocol according to RFC 7345 [217], RFC 8842 [240] and the profile defined in 3GPP TS 33.328 [19C];
- if the SDP offer contains any potential configuration(s) with delete-attribute parameter(s) (see RFC 5939 [137]), (e.g. "a=pcfg:1 a=-sm:1"), remove those potential configuration(s);
- include the SDP fingerprint attribute according to RFC 8122 [241] and the profile defined in 3GPP TS 33.328 [19C];
- include the SDP "a=3ge2ae:applied" attribute; and
- include the SDP tls-id attribute as defined in RFC 8842 [240]; and
2) upon receiving an SDP answer to the SDP offer from remote user, for each accepted end-to-access-edge protected UDPTL based media, the P-CSCF will act as defined in 3GPP TS 23.334 [7F] as far as SDP and UDPTL is concerned, and shall remove the SDP fingerprint attribute and SDP tls-id attribute. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.2.3 IMS-ALG in P-CSCF for explicit congestion control support | |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.2.3.1 General | An IMS-ALG may support ECN according to RFC 6679 [188].
Subject to local policy, an IMS-ALG shall prohibit the negotiation of ECN during SDP offer/answer exchanges associated with multimedia priority service by removing any ECN attribute "a=ecn-capable-rtp" from the SDP offer and shall not invoke ECN for SIP transactions associated with multimedia priority service. |
d3a3ac3f64ab68e4fcef5ea9a665f70a | 24.229 | 6.7.2.3.2 Incoming SDP offer with ECN | If the IMS-ALG receives an SDP offer containing the "a=ecn-capable-rtp" attribute as specified in RFC 6679 [188] and:
- the IMS-ALG knows via configuration that the IMS-AGW supports transparently forwarding of ECN bits according to RFC 3168 [189];
- the IMS-ALG knows via configuration that the (IMS) network handles ECN-marked packets properly; and
- the IMS-ALG does not configure the IMS-AGW to transcode,
then the IMS-ALG shall:
- if the "ecn-capable-rtp" attribute includes both the "ice" initialisation method and other initialisation methods, remove the "ice" initialisation method from the "ecn-capable-rtp" attribute and add the attribute with this modification in the outgoing the SDP offer;
- if the "ecn-capable-rtp" attribute only includes the "ice" initialisation method, do not include the "ecn-capable-rtp" attribute it outgoing SDP offer; and
- if the "ecn-capable-rtp" attribute did not includes the "ice" initialisation method include the unmodified "ecn-capable-rtp" attribute within the outgoing SDP offer.
If the IMS-ALG receives an SDP offer containing the ECN attribute "a=ecn-capable-rtp" as specified in RFC 6679 [188] and any of the following conditions apply:
- the IMS-ALG knows by configuration that the IMS-AGW does not support transparent transport of ECN-marked packets;
- the IMS-ALG knows by configuration that the (IMS) network does not properly handle ECN-marked packets; or
- the IMS-ALG does not configure the IMS-AGW to transcode,
then the IMS-ALG shall not include ECN attributes in the outgoing SDP offer, and, if the IMS-ALG knows in addition via configuration that the IMS-AGW supports acting as an ECN endpoint and that the IMS-ALG supports at least some of the initialisation methods offered within the "a=ecn-capable-rtp" attribute, the IMS-ALG shall:
- select an initialisation method supported by the IMS-AGW; and
- return a SDP answer according to the capabilities of the IMS-AGW, containing the "a=ecn-capable-rtp" attribute,
and the IMS-ALG will configure the IMS-AGW to act as an end point for ECN.
If the IMS-ALG receives an SDP answer containing the "a=ecn-capable-rtp" attribute it will instruct the IMS-AGW to transparently forward the ECN bits described in RFC 3168 [189]. |
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