B.2A Usage of SDP

24.2293GPPIP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP)Release 18Stage 3TS

B.2A.0 General

NOTE: When:

– establishing a session which is not an emergency session; or

– modifying a session which is not an emergency session;

and if the IMSVoPS indicator is received in the "Network feature support" Information Element (see 3GPP TS 24.008 [8]), the UE constructs SDP based on the restrictions indicated in the IMSVoPS indicator. Regardless whether the IMSVoPS indicator indicating voice is supported or not, m-lines can be set to "audio" and exclude voice codecs from the SDP answer or SDP offer.

B.2A.1 Impact on SDP offer / answer of activation or modification of PDP contexts for media by the core network

If due to the activation of PDP context from the core network the related SDP media description needs to be changed the UE shall update the related SDP information by sending, within a SIP request, a new SDP offer for each of the existing SIP dialogs,

If the UE receives a modification request from the core network for a PDP context that is used for one or more media streams in an ongoing SIP session, the UE shall:

1) if, due to the modification of the PDP context, the related SDP media description need to be changed, update the related SDP information by sending, with in a SIP request, a new SDP offer for each of the existing SIP dialogs , and respond to the PDP context modification request.

NOTE: The UE can decide to indicate additional media streams as well as additional or different codecs in the SDP offer than those used in the already ongoing session.

B.2A.2 Handling of SDP at the terminating UE when originating UE has resources available and IP-CAN performs network-initiated resource reservation for terminating UE

If the UE receives an SDP offer where the SDP offer includes all media streams for which the originating side indicated its local preconditions as met, if the precondition mechanism is supported by the terminating UE and the IP-CAN performs network-initiated resource reservation for the terminating UE and the available resources are not sufficient for the received offer the terminating UE shall indicate its local preconditions and provide the SDP answer to the originating side without waiting for resource reservation.

NOTE 1: If the resource reservation is controlled by the GPRS IP-CAN, the resource reservation request is initiated by the core network after the P-CSCF has authorised the respective IP flows and provided the QoS requirements over the Rx interface to the PCRF as described in 3GPP TS 29.214 [13D].

NOTE 2: During the PDP context activation procedure the UE and the core network negotiate whether the UE or the GPRS IP-CAN is responsible for the resource reservation applicable to all PDP contexts within the activated PDP address/APN pair as described in 3GPP TS 24.008 [8].

B.2A.3 Emergency service

NOTE: When establishing an emergency session or when modifying an emergency session, the IMSVoPS indicator does not influence handling of SDP offer and SDP answer.