A.16 SDP offers and answers with QoS hint signalling

26.1143GPPIP Multimedia Subsystem (IMS)Media handling and interactionMultimedia telephonyRelease 18TS

Table A.16.1 demonstrates an example SDP offer with QoS hint signalling defined in clause 6.2.7.4. The offer for QoS hint signalling is indicated in the last line via the SDP attribute ‘3gpp-qos-hint’.

Table A.16.1: Example SDP offer with QoS hint signalling

SDP offer

m=video 43200 RTP/AVP 100 b=AS:15000 b=RS:0 b=RR:2500 a=pcfg:1 t=1 a=rtpmap:100 H265/90000 a=fmtp:100 profile-id=1;level-id=153 a=imageattr:100 send [x=3840,y=2160] a=label:flus a=sendonly a=3gpp-qos-hint:loss=0.00001;latency=300

An example SDP answer is shown in Table A.16.2, where the QoS hint signalling is also supported by the answerer, as indicated by the last line.

Table A.16.2: Example SDP answer with QoS hint signalling

SDP answer

m=video 43200 RTP/AVPF 100 b=AS:15000 b=RS:0 b=RR:2500 a=acfg:1 t=1 a=rtpmap:100 H265/90000 a=fmtp:100 profile-id=1;level-id=153 a=imageattr:100 recv [x=3840,y=2160] a=label:flus a=recvonly a=3gpp-qos-hint:loss=0.00001;latency=300

Table A.16.3 demonstrates an example SDP offer with QoS hint signalling defined in clause 6.2.7.4, using explicit split of the end-to-end values. The offer suggests itself to use less than half of the end-to-end loss, but more than half of the end-to-end latency in the SDP attribute ‘3gpp-qos-hint’.

Table A.16.3: Example SDP offer with QoS hint signalling and explicit split

SDP offer

m=video 43200 RTP/AVP 100 b=AS:15000 b=RS:0 b=RR:2500 a=pcfg:1 t=1 a=rtpmap:100 H265/90000 a=fmtp:100 profile-id=1;level-id=153 a=imageattr:100 send [x=3840,y=2160] a=label:flus a=sendonly a=3gpp-qos-hint:loss=0.00002/local:0.000005;latency=600/local:400

Table A.16.4 demonstrates another example SDP answer where the QoS hint signalling is also supported by the answerer, but where neither the desired QoS hint end-to-end values nor the QoS hint split values from the SDP offer can be supported and are changed in the SDP answer.

Table A.16.4: Example SDP answer with QoS hint signalling changing QoS hint values and split

SDP answer

m=video 43200 RTP/AVPF 100 b=AS:15000 b=RS:0 b=RR:2500 a=acfg:1 t=1 a=rtpmap:100 H265/90000 a=fmtp:100 profile-id=1;level-id=153 a=imageattr:100 recv [x=3840,y=2160] a=label:flus a=recvonly a=3gpp-qos-hint:loss=0.1;latency=500/local:100

The resulting loss hint is 0.05% for both SDP offerer and SDP answerer (half of the provided end-to-end value), which is a significant relaxation in loss rate compared to the offer in Table A.16.3 that might not be sufficient to provide an acceptable user experience. The resulting latency hint is 400 ms (500-100) for the SDP offerer and 100 ms for the SDP answerer, which is stricter end-to-end than the offer in Table A.16.3, but the answerer takes on the stricter latency and leaves the offerer part of the split from the offer (400 ms) unmodified.