scope:

The present document specifically describes the differing SDP usage between SIP [2] and H.248 [3] together with the implied mapping capability that is performed by the MGC/Call Server.

SDP [1] has been widely selected as the protocol of choice within VoIP (or multimedia; MMoIP) to describe the media requirements of a given session/call/connection. However, the different VoIP control protocols that utilise SDP each specify differing requirements in their use of SDP. There is therefore a need for a MGC/Call Server to arbitrate between these variations in the use of SDP and perform the interworking between them.

SDP [1] has been widely selected as the protocol of choice within VoIP (or multimedia; MMoIP) to describe the media requirements of a given session/call/connection. However, the different VoIP control protocols that utilize SDP each specify differing requirements in their use of SDP. There is therefore a need for a MGC/Call Server to arbitrate between these variations in the use of SDP and perform the interworking between them. Specifically for this report, the differing SDP usage between SIP [2] and H.248 [3] shall be described together with the implied mapping capability that is performed by the MGC/Call Server.

Any network element (e.g. a MGCF) which handles both H.248/SDP signalling and SIP/SDP signalling provides any necessary interworking between both signalling protocols. Such interworking comprises in general:

• interworking between SIP and H.248 signalling on message and procedural level (out of scope of the present document); and

• interworking between the two SDP segments (SDP-SDP interworking; the scope of the present document).

The function providing SDP-to-SDP interworking between SIP/SDP and H.248/SDP signalling is, in the present document, termed a "SDP Mapper" (see also clause 3.1).

The SDP Mapper performs SDP-SDP interworking capability to reconcile the different uses of SDP between control protocols H.248 and SIP. In order to perform this role, the SDP Mapper takes into account i) which parts of SDP are required to be sent on an interface, and ii) which parts of SDP are received on an interface. For a given session/call, which use the two different control protocols at each end, some SDP parameters may be transited whilst others may not. The SDP Mapper ensures that the differing requirements with regard to SDP handling at each end are mutually satisfied.