B.6 Support for Early Session disposition SDP

29.5143GPP5G SystemPolicy Authorization ServiceRelease 18Stage 3TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

B.6.1 General

As a network option, when the "IMS_SBI" feature is supported, the P-CSCF may support the PCC procedures in the present clause to handle "early session" disposition type SDP, as standardised in IETF RFC 3959 [38].

B.6.2 Service Information Provisioning for Early Media

The P-CSCF can receive "early session" disposition SDP in addition to "session" disposition SDP in SIP early dialogues.

The P-CSCF shall then provision service information derived both from the "early session" disposition SDP and "session" disposition SDP applying the procedures in clauses B.1, B.2, and B.3, and in the present clause.

The P-CSCF shall apply the mapping rules in Annex C to derive the flow identifiers from "early session" disposition SDP.

If a single media line with one media type (e.g. "audio" or "video") is contained in "early session" disposition SDP and a single media line with the same media type is contained in the "session" disposition SDP of the same SIP dialogue, and both media lines describe service flows of the same directionality (uplink, downlink, or bidirectional), the P-CSCF should describe those SDP media lines in the same session information media component (with the same flow ID).

The "early session" disposition SDP can also contain media lines of a type not included in the "session" disposition SDP, or several media lines of the same type. Such media components shall be described in own media components in the service information.

If the P-CSCF desires to invoke special policies or separate event notifications for an "early session" disposition media line, it may choose to provision a separate session information media component even if a media line with the same media type and directionality is contained in "session" disposition SDP.

NOTE 1: A PCF is then likely to supply separate PCC rules for early media and the corresponding final media. This may lead to an over provisioning of resources during call establishment and a subsequent reconfiguration of the radio bearer, or even to a call failure if the extra resources are not authorized or available.

If the P-CSCF receives "early session" disposition SDP before any "session" disposition SDP and supplies service information derived from the "early session" disposition SDP at this point of time, it shall use dedicated media components relating only to the "early session" disposition SDP in the service information.

NOTE 2: The "session" disposition SDP offer will frequently occur before the "early session" disposition SDP offer, but can also occur in parallel or in exceptional cases afterwards. The "session" disposition SDP answer can be contained in the same SIP message as the "early session" disposition SDP offer, or can be sent in a 200 OK (INVITE), i.e. after the "early session" disposition SDP answer.

If the P-CSCF includes any media component relating both to "early session" disposition SDP and "session" disposition SDP in the service information, the P-CSCF shall:

– provision the service information derived from "early session" disposition SDP and the service information derived from "session" disposition SDP in separate Npcf_PolicyAuthorization_Update requests (to the same "Individual Application Session Context" resource), and shall send a new Npcf_PolicyAuthorization_Update request only after any previous Npcf_PolicyAuthorization_Update request has been acknowledged; and

– provision the first service information (either derived from "early session" disposition SDP or "session" disposition SDP) without the "sipForkInd" attribute, or with "sipForkInd" attribute with value "SINGLE_DIALOGUE"; and

– provision all subsequent service information during ongoing call establishment with the "sipForkInd" attribute with value SEVERAL_DIALOGUES; and

– if an SDP answer has been received and codecs are provisioned within the "codecs" attribute included in a media component of the "medComponents" attribute, provision within a "codecs" attribute the codec derived from the corresponding offer together with a codec derived from the SDP answer.

NOTE 3: The P-CSCF needs to provision the service information derived from "early session" disposition SDP and the service information derived from "session" disposition SDP in separate Npcf_PolicyAuthorization_Update requests because the encoding of the media component does not allow for the simultaneous provisioning of two corresponding filters.

NOTE 4: The PCF will treat service information containing the "sipForkInd" attribute as described in clause B.3.

B.6.3 Updating the Provisioned Service Information when Dialogue is established

The P-CSCF shall store the SDP information for the "session" disposition type until the first final SIP answer is received. Then the early media described in the "early session" disposition type SDP are terminated.

The P-CSCF shall then update the service information to match the requirements of the media described in the "session" disposition type SDP only:

– If the P-CSCF included any media component relating both to "early session" disposition SDP and "session" disposition SDP in the service information, the P-CSCF shall send an Npcf_PolicyAuthorization_Update request without the "sipForkInd" attribute or with a "sipForkInd" attribute with value SINGLE_DIALOGUE and shall include the service information derived from the "session" disposition SDP. The P-CSCF shall provision the full service information including the applicable "fDescs" attribute and "fStatus" attribute.

– The P-CSCF shall disable any media component(s) in the service information that relate to early media only by setting their flow status to "REMOVED".