6.2.16 Coordination of Video Orientation

23.3343GPPIP Multimedia Subsystem (IMS) Application Level Gateway (IMS-ALG) - IMS Access Gateway (IMS-AGW) interface: Procedures descriptionsRelease 17TS

Figure 6.2.16.1 shows the message sequence chart example for indicating extended RTP header for Coordination of Video Orientation.

Figure 6.2.16.1: Procedure to indicate RTP extension header for CVO

This procedure is identical to that of clause 6.2.1 apart from the IMS-ALG optionally requesting the IMS-AGW to support the RTP Header Extension capability as defined in IETF RFC 5285 [23].

NOTE: If the IMS-ALG receives an SDP answer, which includes the "a=extmap" attribute with a CVO URN with a granularity that the IMS-AGW has not included in its response, or if the SDP answer does not include any "a=extmap" CVO related attribute, it is not necessary to modify the IMS-AGW settings for this reason alone. Doing that would only add unnecessary signalling without requiring any action or changes in the IMS-AGW. However, if the IMS-ALG needs to modify the media attributes for other purposes, in particular due to transcoding, then the IMS-AGW is updated in accordance with the received SDP answer, that is, either with the received CVO related "a=extmap" attribute if present in the received SDP answer or without it if not included in the received SDP answer (thus removing the requirement for supporting "a=extmap" and for sending the header and CVO bits for the transcoded stream).