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5.7.1.28.1 RCD info retrieval
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The AS may support RCD and receive RCD server address, RCD information or RCD URL from the HSS via the Nhss_ImsSubscriberDataManagement (ImsSDM) service, as described in 3GPP TS 29.562 [274].
If the AS received the RCD URL from the HSS, the AS may, based on configuration, retrieve the RCD information from the RCD server using the RCD URL.
NOTE: The interface between the AS and RCD server is out of scope of 3GPP.
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5.7.1.28.2 Originating procedures
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If the AS received an initial INVITE request or MESSAGE request, the RCD info as defined in draft-ietf-sipcore-callinfo-rcd [303] is not included in the received request, support of the RCD is required by the local policy and the AS retrieved the RCD info as described in subclause 5.7.1.28.1, the AS may insert in the initial INVITE request or MESSAGE request the Call-Info header field as specified in draft-ietf-sipcore-callinfo-rcd [303].
Editor's note: [WI: NG_RTC_Ph2, CR#6714] Adding of Call-Info header field with RCD info for the served user which activated the OIR service is FFS.
Editor's note: [WI: NG_RTC_Ph2, CR#6714] Update of the From or P-Asserted-Identity header field to include calling name from RCD information in a "display name" component is FFS.
If the AS supports RCD verification using assertion of RCD info as specified in subclause 3.1 and required by the local policy, the AS shall perform signing of RCD info included in the Call-Info header field of the initial INVITE request or MESSAGE request as specified in subclause 5.7.1.25.2.
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5.7.1.28.3 Terminating procedures
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If the AS supports RCD verification using assertion of RCD info as specified in subclause 3.1, required by the local policy, the AS received an initial INVITE request or MESSAGE request containing the Call-Info header field with RCD info and one or more Identity header fields, the AS may perform signature verification of the RCD info as specified in subclause 5.7.1.25.3.
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5.7.2 Application Server (AS) acting as terminating UA, or redirect server
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When acting as a terminating UA the AS shall behave as defined for a UE in subclause 5.1.4, with the exceptions identified in this subclause.
The AS, 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.
If the AS requires knowledge of the served user it shall determine the served user according to the applicable procedure in subclause 5.7.1.3A.
An AS acting as redirect server shall propagate any received IM CN subsystem XML message body in the redirected message.
When an AS acting as a terminating UA generates a subsequent request for a dialog, the AS shall insert a P-Charging-Vector header field with the "icid-value" header field parameter set to the value populated in the initial request for the dialog and a type 3 "orig-ioi" header field parameter. The AS shall set the type 3 "orig-ioi" header field parameter to a value that identifies the service provider from which the request is sent. The AS shall not include the type 3 "term-ioi" header field parameter.
When the AS acting as terminating UA receives a request, the AS shall store the value of the "orig-ioi" header field parameters received in the P-Charging-Vector header field if present.
NOTE 1: Any received orig-ioi parameter will be a type 3 orig-ioi. The orig-ioi identifies the network operator from which the request was sent.
When the AS acting as terminating UA generates a response to a request, the AS 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 AS 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.
The AS acting as terminating UA receiving an initial request with a P-Charging-Vector header field shall, based on local policy, store the "fe-identifier" header field parameter of the P-Charging-Vector header field.
The AS acting as terminating UA shall, based on local policy, include the stored "fe-identifier" header field parameter in the P-Charging-Vector header field, add its address or identifier and application id to the "as-addr" and "as-id" elements of the "fe-identifier" header field parameter of the P-Charging-Vector header field and send the P-Charging-Vector header field in the related final response.
NOTE 2: An AS hosting multiple applications can add multiple pairs of "as-addr" and "as-id" header field parameters when executing these applications.
If resource priority in accordance with RFC 4412 [116] is required for a dialog, then the AS shall include the Resource-Priority header field in all requests associated with that dialog. If priority is supported, the AS shall take into account that subsequent received SIP requests or responses within the same dialog or transaction may have added or changed the Resource-Priority header field or backwards indication.
NOTE 3: An AS can modify the priority using the Resource-Priority header field in a dialog on behalf of a user. The mechanism for a user to invoke this AS action is out of scope of this release of the specification.
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5.7.3 Application Server (AS) acting as originating UA
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In order to support an AS acting as an originating UA, the AS has to be within the same trust domain as the S-CSCF to which requests will be sent.
When acting as an originating UA the AS shall behave as defined for a UE in subclause 5.1.3, with the exceptions identified in this subclause.
The AS, although acting as a UA, does not initiate any registration of its associated addresses and does not participate in any authentication procedures defined for a UE. These are assumed to be known by peer-to-peer arrangements within the IM CN subsystem.
When an AS acting as an originating UA generates an initial request for a dialog or a request for a standalone transaction, the AS shall insert 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 AS shall set the type 3 "orig-ioi" header field parameter to a value that identifies the service provider from which the request is sent. The AS shall not include the type 3 "term-ioi" header field parameter.
NOTE 1: The AS can retrieve CDF and/or ODF addresses from HSS on Sh interface.
When the AS acting as an originating UA receives any response to a request, the AS shall store the value of the "term-ioi" header field parameter received in the P-Charging-Vector header field if present.
NOTE 2: Any received "term-ioi" header field parameter will be a type 3 IOI. The type 3 IOI identifies the network operator from which the response was sent.
When an AS acting as an originating UA generates a subsequent request for a dialog, the AS shall insert a P-Charging-Vector header field with the "icid-value" header field parameter set to the value populated in the initial request for the dialog and a type 3 "orig-ioi" header field parameter. The AS shall set the type 3 "orig-ioi" header field parameter to a value that identifies the service provider from which the request is sent. The AS shall not include the type 3 "term-ioi" header field parameter.
Based on local policy, the AS acting as an originating UA or application(s) hosted by the AS acting as originating UA shall add an "as-addr" and an "as-id" element of the "fe-identifier" header field parameter to the P-Charging-Vector header field with its own address or identifier and application identifier to an initial request.
NOTE 3: An AS hosting multiple applications can add multiple pairs of "as-addr" and "as-id" header field parameters when executing these applications for an initial request.
The AS shall extract charging function addresses from any P-Charging-Function-Addresses header field that is received in any 1xx or 2xx responses to the requests.
The AS may also indicate that the proxies should not fork the request by including a "no-fork" directive within the Request-Disposition header field in the request as described in RFC 3841 [56B].
When sending any initial request, an identity is needed that will correlate with the service profile to be used at the S-CSCF. If the identity for that service profile corresponds to the value to be used to identify the caller to the destination user, include the identity in the P-Asserted-Identity header field. If the identity for that service profile does not correspond to the value to be used to identify the caller to the destination user, and the P-Served-User header field is supported by the S-CSCF, include the identity in the P-Served-User header field. This leaves the P-Asserted-Identity header field for the identity to be used to identify the caller to the destination user. If the identity for that service profile matches a wildcarded identity and the P-Profile-Key header field is supported by the AS, include the wildcarded identity in the P-Profile-Key header field.
When sending an initial request on behalf of a PSI that is hosted by the AS, the AS shall:
- insert a Request-URI as determined by the service logic;
- insert a P-Asserted-Identity header field and possibly a P-Served-User header field containing the PSI as indicated earlier in this subclause;
- if the AS is not able to resolve the next hop address by itself or the operator policy does not allow it, insert a Route header field pointing either to the S-CSCF where the PSI is hosted, or to the entry point of the home network of the PSI or to the transit function. The AS shall append the "orig" parameter to the URI in the topmost Route header field; and
NOTE 4: The address of the S-CSCF hosting the PSI can be obtained by querying the HSS on the Sh interface.
NOTE 5: AS can only send the initial request to the entry point of the home network of the PSI only if the AS can assume (e.g. based on local configuration) that the receiving entry point will be able to process the request as an originating request.
- if the AS is able to resolve the next hop address by itself and the operator policy allows it, forward the originating request directly to the destination without involving any S‑CSCF in the originating IM CN subsystem.
When sending an initial request on behalf of a public user identity, the AS shall:
- insert a Request-URI as determined by the service logic;
- insert a P-Asserted-Identity header field and possibly a P-Served-User header field containing the public user identity as indicated earlier in this subclause;
- if the AS intends to send the originating request to the home network of the public user identity or the operator policy requires it, insert a Route header field pointing to the S-CSCF where the public user identity on whose behalf the request is generated is registered or hosted (unregistered case) or to the entry point of the public user identity's network. The AS shall append the "orig" parameter to the URI in the topmost Route header field; and
NOTE 6: The address of the S-CSCF can be obtained either by querying the HSS on the Sh interface or during third-party registration.
NOTE 7: AS can send the initial request to the entry point of the public user identity's network or to the entry point of the home network of the PSI only if the AS can assume (e.g. based on local configuration) that the receiving entry point will be able to process the request as an originating request.
- if the AS intends to send the originating request directly to the terminating network and the operator policy allows it, forward the originating request directly to the destination without involving any S‑CSCF in the originating IM CN subsystem.
When sending an initial request to a served public user identity, the AS shall insert:
- a Request-URI containing the served public user identity;
- a P-Asserted-Identity as determined by the service logic (e.g. the URI of the AS or the URI of the entity that triggered the SIP request, if the sending of the initial request is triggered by a non-SIP request); and
- a Route header field pointing to the S-CSCF where the public user identity to whom the request is generated is registered or hosted (unregistered case) or to the entry point of the public user identity's network. The AS shall not append the "orig" parameter to the URI in the topmost Route header field.
NOTE 8: The address of the S-CSCF can be obtained either by querying the HSS on the Sh interface or during third-party registration.
The AS can indicate privacy of the P-Asserted-Identity in accordance with RFC 3323 [33], and the additional requirements contained within RFC 3325 [34].
Where privacy is required, in any initial request for a dialog or request for a standalone transaction, the AS shall set a display-name of the From header field to "Anonymous" as specified in RFC 3261 [26] and set an addr-spec of the From header field to Anonymous User Identity as specified in 3GPP TS 23.003 [3].
NOTE 9: The contents of the From header field cannot be relied upon to be modified by the network based on any privacy specified by the user either within the AS indication of privacy or by network subscription or network policy. Therefore the AS includes the value "Anonymous" whenever privacy is explicitly required.
If resource priority in accordance with RFC 4412 [116] is required for a dialog, then the AS shall include the Resource-Priority header field in all requests associated with that dialog. If priority is supported, the AS shall take into account that subsequent received SIP requests or responses within the same dialog or transaction may have added or changed the Resource-Priority header field or backwards indication.
NOTE 10: An AS can modify the priority using the Resource-Priority header field in a dialog on behalf of a user. The mechanism for a user to invoke this AS action is out of scope of this release of the specification.
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5.7.4 Application Server (AS) acting as a SIP proxy
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When the AS acting as a SIP proxy receives a request from the S-CSCF, prior to forwarding the request, the AS shall:
- remove its own URI from the topmost Route header field;
- if the request contains a "logme" header field parameter in the SIP Session-ID header field then log the request if required by local policy; and
- after executing the required services, route the request based on the topmost Route header field.
When the AS acting as a SIP proxy receives any response to the above request, the AS shall:
- if the response contains a "logme" header field parameter in the SIP Session-ID header field then log the request if required by local policy.
The AS may modify the SIP requests based on service logic, prior to forwarding the request back to the S-CSCF.
The AS shall not fork the request if the fork-directive in the Request-Disposition header field is set to "no-fork" as described in RFC 3841 [56B].
If the AS requires knowledge of the served user it shall determine the served user according to the applicable procedure in subclause 5.7.1.3A.
An AS acting as a SIP proxy shall propagate any received IM CN subsystem XML message body in the forwarded message.
When the AS acting as a SIP proxy receives a request, the AS shall store the value of the "orig-ioi" header field parameter received in the P-Charging-Vector header field if present. The AS shall remove the "orig-ioi" header field parameter from the forwarded request and insert a type 3 "orig-ioi" header field parameter. The AS shall set the type 3 "orig-ioi" header field parameter to a value that identifies the service provider from which the request is sent. The AS shall not include the type 3 "term-ioi" header field parameter.
NOTE 1: A received orig-ioi parameter will be a type 3 orig-ioi. The orig-ioi identifies the network operator from which the request was sent.
When the AS acting as a SIP proxy forwards a response to a request, the AS shall remove any received "orig-ioi" and "term-ioi" header field parameters, and insert a P-Charging-Vector header field containing the previously stored "orig-ioi" header field parameter, if received in the request and a type 3 "term-ioi" header field parameter. The AS shall set the type 3 "term-ioi" header field parameter to a value that identifies the service provider from which the response is sent and the "orig-ioi" header field parameter is set to the previously received value of "orig-ioi" header field parameter. Any values of "orig-ioi" or "term-ioi" header field parameters received in any response that is being forwarded are not used.
Based on local policy, the AS acting as a SIP proxy shall add an "as-addr" and an "as-id" element of the "fe-identifier" header field parameter to the P-Charging-Vector header field with its own address or identifier and application identifier.
NOTE 2: An AS hosting multiple applications can add multiple pairs of "as-addr" and "as-id" header field parameters when executing these applications for an initial request.
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5.7.5 Application Server (AS) performing 3rd party call control
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5.7.5.1 General
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The AS performing 3rd party call control acts as a B2BUA. There are two kinds of 3rd party call control:
- Routeing B2BUA: an AS receives a request, terminates it and generates a new request, which is based on the received request.
- Initiating B2BUA: an AS initiates two requests, which are logically connected together at the AS, or an AS receives a request and initiates a new request that is logically connected but unrelated to the incoming request from the originating user (e.g. the P-Asserted-Identity of the incoming request is changed by the AS). AS can initiate additional requests and associate them with a related incoming request.
When the AS acting as an initiating B2BUA receives a request and initiates a new request that is logically connected but unrelated to the incoming request from the originating user, the AS can include an original dialog identifier in the Route header field for the S-CSCF that it learned from the incoming request, per service logic needs.
NOTE 1: If the AS does not include the original dialog identifier in an initiated request, the S-CSCF can apply the default handling procedure relating to the incoming request if after a certain time no 1xx response is sent by the AS to the incoming request or if the AS forwards a 408 (Request Timeout) response or a 5xx response received from downstream as a response to the incoming request. To avoid the application of the default handling procedure by the S-CSCF when the AS is waiting for a SIP response for an initiated request, the AS can generate a SIP provisional response to the incoming request.
If the AS requires knowledge of the served user the AS shall determine the served user according to the applicable procedure in subclause 5.7.1.3A.
When the AS receives a terminated call and generates a new call, and dependent on whether the service allows the AS to change the P-Asserted-Identity for outgoing requests compared with the incoming request, the AS will select appropriate kind of 3rd party call control.
The B2BUA AS 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. These decisions are specific to each AS and are outside the scope of the present document.
The AS, 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.
For standalone transactions, when the AS is acting as a Routeing B2BUA, the AS shall copy the remaining Route header field(s) unchanged from the received request for a standalone transaction to the new request for a standalone transaction.
When the AS receives a Replaces header field within an initial request for a dialog, the AS should check, whether the AS acts as a routeing B2BUA for the dialog identified in the Replaces header field. The AS should:
- if the AS acts as routeing B2BUA for the dialog indicated in the Replaces header field, include in the forwarded request a Replaces header field, indicating the dialog on the outgoing side that corresponds to the dialog identified in the received Replaces header field; or
- if the AS does not act as a routeing B2BUA for the dialog indicated in the Replaces header field, include in the forwarded request the Replaces header field as received in the incoming request.
When the AS receives a Target-Dialog header field within an initial request or a standalone transaction for a dialog, the AS shall:
- if the AS acts as routeing B2BUA for the dialog indicated in the Target-Dialog header field, include in the forwarded request a Target-Dialog header field, indicating the dialog on the outgoing side that corresponds to the dialog identified in the received Target-Dialog header field.
When the AS acting as a routeing B2BUA receives a request, the AS shall:
- store the value of the "orig-ioi" header field parameter received in the P-Charging-Vector header field if present; and
- remove the "orig-ioi" header field parameter from the forwarded request.
NOTE 2: Any received orig-ioi parameter will be a type 3 orig-ioi. The orig-ioi identifies the network operator from which the request was sent.
When an AS acts as a routeing B2BUA and the received Contact header field contains a media feature tag indicating a capability for which the Contact URI can be used by the remote party, the AS shall transparently forward the Contact header field. When transparently forwarding a received Contact header field of a dialog-forming request, the AS 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 3: One example of such a media feature tag is the isfocus media feature tag where the URI in the Contact header field is used by conference services to transport the temporary conference identity that can be used when rejoining an ongoing conference.
When the AS acting as a routeing B2BUA generates a response to a request, the AS 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 AS 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. Any values of "orig-ioi" or "term-ioi" header field parameter received in any response that is being forwarded are not used.
The AS shall transparently pass supported and unsupported signalling elements (e.g. SIP headers, SIP messages bodies), except signalling elements that are modified or deleted as part of the hosted service logic, or based on service provider policy.
If resource priority in accordance with RFC 4412 [116] is required for a dialog, then the AS shall include the Resource-Priority header field in all requests associated with that dialog. If priority is supported, the AS shall take into account that subsequent received SIP requests or responses within the same dialog or transaction may have added or changed the Resource-Priority header field or backwards indication.
The AS 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.
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5.7.5.2 Call initiation
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5.7.5.2.1 Initial INVITE
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When the AS acting as a Routeing B2BUA receives an initial INVITE request, the AS shall:
1) remove its own SIP URI from the topmost Route header field of the received INVITE request;
2) perform the AS specific functions. See 3GPP TS 23.218 [5];
3) if successful, generate and send a new INVITE request to establish a new dialog;
4) copy the remaining Route header field(s) unchanged from the received INVITE request to the new INVITE request;
5) copy the P-Asserted-Identity to the outgoing request;
6) if a Route header field is present, route the new INVITE request based on the topmost Route header field; and
NOTE 1: The topmost Route header field of the received INVITE request will contain the AS's SIP URI. The following Route header field will contain the SIP URI of the S-CSCF.
7) if no Route header field is present (e.g. the AS may be acting on behalf of a PSI):
a) insert a Route header field pointing either to the S-CSCF where the PSI is hosted or to the entry point of the home network of the PSI or to the transit function, if the AS is not able to resolve the next hop address by itself or the operator policy requires it; or
b) forward the originating request directly to the destination without involving any S‑CSCF in the originating IM CN subsystem, if the AS is able to resolve the next hop address by itself, and the operator policy allows it.
NOTE 2: The address of the S-CSCF hosting the PSI can be obtained by querying the HSS on the Sh interface.
When the AS is acting as an Initiating B2BUA, the AS shall apply the procedures described in subclause 5.7.3 for any outgoing requests. The AS shall either set the "icid-value" header field parameter in the P-Charging-Vector header field to be the same as received or different.
NOTE 3: The AS can retrieve CDF and/or ODF adresses from HSS on Sh interface.
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5.7.5.2.2 Subsequent requests
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If the policy or service logic requires the AS to check whether the session is still alive, the AS shall send UPDATE requests periodically to the served UE. The UPDATE requests shall not contain SDP offer.
NOTE: The exact timing of sending the UPDATE requests is out of scope of this specification. Sending UPDATE requests too frequently can increase the load on the network and increase the probability of interactions delaying urgent requests (e.g., those related to session transfers). RFC 4028 [58] provides additional information on the problems caused by sending too frequest SIP "keep alives" and provides recommendations on suitable timer values to avoid such issues.
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5.7.5.3 Call release
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An AS may initiate a call release. See 3GPP TS 23.218 [5] for possible reasons. The AS shall simultaneously send the BYE request for both dialogs managed by the B2BUA.
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5.7.5.4 Call-related requests
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Void.
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5.7.5.5 Further initial requests
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When the AS is acting as an Initiating B2BUA the AS shall apply the procedures described in subclause 5.7.3 for the requests. The AS shall either set the "icid-value" header field parameter in the P-Charging-Vector header field to be the same as received or different. The AS may initiate any number of requests, per service logic needs.
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5.7.5.6 Transcoding services invocation using third-party call control
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An AS may invoke transcoding at an MRFC by the use of RFC 4117 [166], if the MRFC supports acting as the transcoding server described in RFC 4117 [166].
During the call setup, an AS may decide proactively to invoke transcoding when receiving an INVITE request, or reactively when the callee rejects the call setup using a 488 (Not Acceptable Here) response. To invoke transcoding using RFC 4117 [166], the AS shall act as a B2BUA between caller and callee and establish a third SIP dialogue towards the MRFC, supporting the transcoding as defined in subclause 6.6.
The SIP messages relating to the dialogue between AS and MRFC are sent either via the S-CSCF over the ISC and Mr interfaces, or directly over the Mr' interface.
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5.7.6 Void
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5.8 Procedures at the MRFC
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5.8.1 General
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Although the MRFC is acting as a UA, it is outside the scope of this specification how the MRFC associated addresses are made known to other entities.
For all SIP transactions identified:
- if priority is supported, as containing an 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 MRFC shall give priority over other transactions or dialogs. This allows special treatment of such transactions or dialogs. If priority is supported, the MGCF 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: This 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.
When the MRFC sends any request or response (excluding CANCEL requests and responses) related to a dialog or standalone transaction, the MRFC may insert previously saved values into P-Charging-Vector header field before sending the message.
When the MRFC sends any request or response (excluding ACK requests and CANCEL requests and responses) related to a dialog or standalone transaction, the MRFC may insert previously saved values into P-Charging-Function-Addresses header fields before sending the message.
The MRFC shall use a GRUU referring to itself (as specified in RFC 5627 [93]) when inserting a contact address in a dialog establishing or target refreshing SIP message. This specification does not define how GRUUs are created by the MRFC; they can be provisioned by the operator or obtained by any other mechanism. A GRUU used by the MRFC when establishing a dialog shall remain valid for the lifetime of the dialog.
The MRFC shall handle requests addressed to its currently valid GRUUs when received outside of the dialog in which the GRUU was provided.
EXAMPLE: Upon receipt of an INVITE request addressed to a GRUU assigned to a dialog it has active, and containing a Replaces header field referencing that dialog, the MRFC will be able to establish the new call replacing the old one.
The MRFC 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 MRFC 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 "mrfc" and optionally an appropriate fe-param part of the URN set in accordance with subclause 7.2.17.
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5.8.2 Call initiation
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5.8.2.1 Initial INVITE
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5.8.2.1.1 MRFC-terminating case
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5.8.2.1.1.1 Introduction
The MRFC shall provide a P-Asserted-Identity header field in a response to the initial request for a dialog, or any response for a standalone transaction. It is a matter of network policy whether the MRFC expresses privacy according to RFC 3323 [33] with such responses.
When the MRFC receives an initial INVITE request, the MRFC shall store the values received in the P-Charging-Vector header field, e.g. "icid-value" header field parameter. The MRFC shall store the values received in the P-Charging-Function-Addresses header field.Based on local policy, the MRFC 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.
If the MRFC receives an initial request with a P-Charging-Vector header field, the MRFC shall, based on local policy, store the "fe-identifier" header field parameter of the P-Charging-Vector header field.
When the MRFC receives a final response, the MRFC shall, based on local policy, include the stored "fe-identifier" header field parameter in 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.
5.8.2.1.1.2 Tones and announcements
The MRFC can receive INVITE requests to set up a session to play tones and announcements. The MRFC acts as terminating UA in this case.
When the MRFC receives an INVITE request for a tone or announcement, the MRFC shall:
- send 100 (Trying) response.
5.8.2.1.1.3 Ad-hoc conferences
The MRFC can receive INVITE requests to set up an ad-hoc conferencing session (for example a multiparty call) or to add parties to the conference. The MRFC acts as terminating UA in this case.
When the MRFC receives an INVITE request for ad hoc conferencing, the MRFC shall:
- send 100 (Trying) response.
When the MRFC receives an INVITE request to add a party to an existing ad hoc conference (i.e. MRFC conference identifier), the MRFC shall:
- send 100 (Trying) response.
5.8.2.1.1.4 Transcoding
The MRFC may receive INVITE requests to set up transcoding between endpoints with incompatible codecs. The MRFC acts as terminating UA in this case.
When the MRFC receives an INVITE request for transcoding and a codec is supplied in SDP, the MRFC shall:
- send 100 (Trying) response.
When the MRFC receives an INVITE request with an indicator for transcoding but no SDP, the MRFC shall:
- send 183 (Session Progress) response with list of codecs supported by the MRFC/MRFP.
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5.8.2.1.2 MRFC-originating case
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The MRFC shall provide a P-Asserted-Identity header field in an initial request for a dialog, or any request for a standalone transaction. It is a matter of network policy whether the MRFC expresses privacy according to RFC 3323 [33] with such requests.
When an MRFC generates an initial request for a dialog or a request for a standalone transaction, the MRFC shall insert a P-Charging-Vector header field with the "icid-value" header field parameter populated as specified in 3GPP TS 32.260 [17].
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5.8.2.2 Subsequent requests
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5.8.2.2.1 Tones and announcements
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When the MRFC receives an ACK request for a session, this may be considered as an event to direct the MRFP to start the playing of a tone or announcement.
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5.8.2.2.2 Transcoding
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When the MRFC receives a PRACK request (in response to the 183 (Session Progress) response with an indicator for transcoding and codec supplied in SDP, the MRFC shall:
- after the MRFP indicates that the transcoding request is granted, send 200 (OK) response.
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5.8.3 Call release
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5.8.3.1 S-CSCF-initiated call release
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5.8.3.1.1 Tones and announcements
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When the MRFC receives a BYE request for a session, the MRFC directs the MRFP to stop the playing of a tone or announcement.
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5.8.3.2 MRFC-initiated call release
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5.8.3.2.1 Tones and announcements
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When the MRFC has a timed session to play tones and announcements and the time expires, the MRFC shall:
- send a BYE request towards the UE.
When the MRFC is informed by the MRFP that tone or announcement resource has been released, the MRFC shall:
- send a BYE request towards the UE.
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5.8.4 Call-related requests
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5.8.4.1 ReINVITE
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5.8.4.1.1 MRFC-terminating case
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5.8.4.1.1.1 Ad-hoc conferences
The MRFC can receive reINVITE requests to modify an ad-hoc conferencing session (for example a multiparty call) for purposes of floor control and for parties to leave and rejoin the conference.
When the MRFC receives a reINVITE request, the MRFC shall:
- send 100 (Trying) response; and
- after the MRFP indicates that the conferencing request is granted, send 200 (OK) response. The MRFC may choose to send a 183 (Session Progress) response prior to the 200 (OK) response.
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5.8.4.1.2 MRFC-originating case
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Void.
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5.8.4.2 REFER
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5.8.4.2.1 MRFC-terminating case
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Void.
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5.8.4.2.2 MRFC-originating case
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Void.
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5.8.4.2.3 REFER initiating a new session
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Void.
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5.8.4.2.4 REFER replacing an existing session
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Void.
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5.8.4.3 INFO
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Void.
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5.8.5 Further initial requests
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When the MRFC responds to an OPTIONS request with a 200 (OK) response, the MRFC may include a message body with an indication of the supported tones/announcement packages, DTMF capabilities, supported codecs and conferencing options of the MRFC/MRFP.
NOTE: As specified in RFC 6230 [146] an MRFC supporting the use of the control channel framework shall support the SYNC command to indicate the media control packages supported. Additionally each media control package should define an audit command for discovery of package capabilities (for example supported codecs and options).
5.8A Procedures at the MRB
For all SIP transactions identified:
- if priority is supported, as containing an 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 MRB shall give priority over other transactions or dialogs. This allows special treatment of such transactions or dialogs. If priority is supported, the MRB 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: This 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.
The MRB 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.
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5.9 Void
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5.9.1 Void
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5.10 Procedures at the IBCF
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5.10.1 General
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As specified in 3GPP TS 23.228 [7] border control functions may be applied between two IM CN subsystems or between an IM CN subsystem and other SIP-based multimedia networks based on operator preference. The IBCF may act both as an entry point and as an exit point for a network. If it processes a SIP request received from other network it functions as an entry point (see subclause 5.10.3) and it acts as an exit point whenever it processes a SIP request sent to other network (see subclause 5.10.2).
The functionalities of the IBCF are entry and exit point procedures as defined in subclause 5.10.2 and subclause 5.10.3 and additionally can include:
- network configuration hiding (as defined in subclause 5.10.4);
- application level gateway (as defined in subclause 5.10.5);
- transport plane control, i.e. QoS control (as defined in subclause 5.10.5);
- screening of SIP signalling (as defined in subclause 5.10.6);
- inclusion of an IWF if appropriate;
- media transcoding control (as defined in suclause 5.10.7);
- privacy protection (as defined in subclause 5.10.8);
- additional routeing functionality (as defined in Annex I); and
- invocation of an AS over the Ms reference point (as defined in subclause 5.10.10).
NOTE 1: The functionalities performed by the IBCF are configured by the operator, and it is network specific.
The IBCF 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 an IBCF acting as an exit or an entry point receives a SIP request, the IBCF may reject the SIP request based on local policy by sending an appropriate SIP 4xx response.
NOTE 2: The local policy can take bilateral agreements between operators into consideration.
NOTE 3: Some SIP requests can be rejected by an AS instead of the IBCF according to local policy.
The IBCF, acting as B2BUA, which is located between visited network and home network shall preserve the dialog identifier, i.e. shall not change the Call-Id header field value, the "tag" header field parameter value of the From header field in any SIP INVITE request and any SIP response to the SIP INVITE request, and shall preserve the "tag" header field parameter value of the To header field, in any SIP response to the SIP INVITE request.
NOTE 4: The IBCF can identify whether it is located between visited network and home network based on local configuration or, if IBCF supports indicating traffic leg associated with a URI as specified in RFC 7549 [225], based on the value of the "iotl" SIP URI parameter.
If the IBCF has verified that an initial INVITE request is for a PSAP callback, then depending on local policy it may include a Priority header field with a "psap-callback" header field value in the INVITE request. If the IBCF included the Priority header field with a "psap-callback" header field value, if the IBCF supports priority verification using assertion of priority information as specified in subclause 3.1 and if required by operator policy, the IBCF shall add a Resource-Priority header field containing a namespace of "esnet" as defined in RFC 7135 [197] if not already present.
NOTE 5: The means for the IBCF to verify that a request is for a PSAP callback is outside the scope of this specification.
When receiving a dialog creating SIP request or a SIP stand-alone request and if an IBCF acting as an entry or exit point supports indicating the traffic leg as specified in RFC 7549 [225], the IBCF can identify the II-NNI traversal scenario as described in subclause 4.13 and make policy decisions based on the II-NNI traversal scenario type. If a received request contains more than one "iotl" SIP URI parameter the IBCF shall select one of the "iotl" SIP parameters in the received request in accordance with the RFC 7549 [225].
When sending a failure response to any received request, depending on operator policy, the IBCF 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 "ibcf" and optionally an appropriate fe-param part of the URN set in accordance with subclause 7.2.17.
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5.10.2 IBCF as an exit point
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5.10.2.1 Registration
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When IBCF receives a REGISTER request, the IBCF shall:
1) void;
2) if network topology hiding is required or IBCF is configured to perform application level gateway and/or transport plane control functionalities, then the IBCF shall add its own routeable SIP URI to the top of the Path header field; and
NOTE 1: 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 2: 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) select an entry point of the home network and forward the request to that entry point.
If the selected entry point:
- 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 entry point and forward the REGISTER request to that entry point.
NOTE 3: The list of the entry points can be either obtained as specified in RFC 3263 [27A] or provisioned in the IBCF. The entry point can be an IBCF or an I-CSCF.
If the IBCF fails to forward the REGISTER request to any entry point, the IBCF shall send back a 504 (Server Time-Out) response to the P-CSCF, in accordance with the procedures in RFC 3261 [26].
5.10.2.1A General
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 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: 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 exit point shall add in responses in the P-Charging-Vector header field a "transit-ioi" header field parameter with an entry which identifies the operator network which the response is transitting or with a void entry.
Based on local policy the IBCF shall delete or void in responses in the P-Charging-Vector header field any received "transit-ioi" header field parameter value.
If an IBCF in the originating visited network, supporting barring of premium numbers when roaming, receives a request to be sent towards the originating home network and the request is originated from a roaming UE and the Request-URI contains an E.164 number encoded as described in subclause 5.1.2A.1.2 which the IBCF is able to identify as a premium rate number in the country of the served network, the IBCF shall, based on local policy, add the "premium-rate" tel URI parameter specified in subclause 7.2A.17 set to a value "information" or "entertainment" as appropriate.
NOTE 2: The feature barring of premium numbers when roaming can be implemented in the P-CSCF or an IBCF of the visited network. Local policy ensures that the feature is only activiated in one of the two.
NOTE 3: If the visited network supports indicating traffic leg as specified in RFC 7549 [225] the above request includes the "iotl" SIP URI parameter with the value "visitedA-homeA" in the bottommost Route header field.
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5.10.2.2 Initial requests
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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.
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5.10.2.3 Subsequent requests
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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].
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5.10.2.4 IBCF-initiated call release
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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.
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5.10.3 IBCF as an entry point
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5.10.3.1 Registration
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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.
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5.10.3.2 Initial requests
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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.
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5.10.3.3 Subsequent requests
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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].
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5.10.3.4 IBCF-initiated call release
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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.
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5.10.3.5 Abnormal cases
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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.
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5.10.4 THIG functionality in the IBCF
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5.10.4.1 General
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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.
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5.10.4.2 Encryption for network topology hiding
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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
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5.10.4.3 Decryption for network topology hiding
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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.
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5.10.5 IMS-ALG functionality in the IBCF
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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.
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5.10.6 Screening of SIP signalling
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5.10.6.1 General
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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.
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5.10.6.2 IBCF procedures for SIP header fields
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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.
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5.10.6.3 IBCF procedures for SIP message bodies
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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].
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5.10.7 Media transcoding control
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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.
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5.10.8 Privacy protection at the trust domain boundary
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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:anonymous@anonymous.invalid>;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.
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5.10.9 Roaming architecture for voice over IMS with local breakout
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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.
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5.10.10 HTTP procedures over the Ms reference point
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5.10.10.1 General
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General procedures over the Ms reference point are specified in clause V.2.
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5.10.10.2 Procedures for an IBCF acting as an entry point
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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.
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5.10.10.3 Procedures for an IBCF acting as an exit point
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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.
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5.11 Procedures at the E-CSCF
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5.11.1 General
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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.
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5.11.2 UE originating case
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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.
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5.11.3 Use of an LRF
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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.
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5.11.4 Subscriptions to E-CSCF events
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5.11.4.1 Subscription to the event providing dialog state
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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.
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5.11.4.2 Notification about dialog state
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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.
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5.11.4.3 Subscription to the presence event package
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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.
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5.11.4.4 Notification about presence
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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.
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5.11.5 Current location discovery during an emergency call
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5.11.5.1 General
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The UE can be requested to provide the current location information during an emergency call.
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5.11.5.2 Requesting current location informaton
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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.
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5.11.5.3 Receiving current location informaton
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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.
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5.12 Location Retrieval Function (LRF)
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5.12.1 General
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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.
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5.12.2 Treatment of incoming initial requests for a dialog and standalone requests
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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.
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5.12.3 Subscription and notification
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5.12.3.1 Notification about dialog state
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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.
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5.12.3.2 Notification about UE location
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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.
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5.13 ISC gateway function
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5.13.1 General
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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.
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5.13.2 ISC gateway function as an exit point
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5.13.2.1 Registration
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There are no specific requirements for the REGISTER method, i.e. the REGISTER method is treated as for other SIP methods.
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5.13.2.2 General
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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.
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5.13.2.3 Initial requests
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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.
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5.13.2.4 Subsequent requests
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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].
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5.13.2.5 Call release initiated by ISC gateway function
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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.
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5.13.3 ISC gateway function as an entry point
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