A.12 SDP examples when using ECN
26.1143GPPIP Multimedia Subsystem (IMS)Media handling and interactionMultimedia telephonyRelease 18TS
A.12.1 SDP examples when using ECN for speech
A.12.1.1 With RTP/AVP and zero RTCP bandwidth
The following SDP offer and SDP answer are likely when both MTSI clients in terminals use ECN for speech.
This SDP example is based on the SDP example found in Table A.3.0 except that bandwidth information for the media has been added, zero RTCP bandwidth has been negotiated, and AVPF is not offered.
Table A.12.1.1: SDP example
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SDP offer |
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m=audio 49152 RTP/AVP 97 98 b=AS:30 b=RS:0 b=RR:0 a=rtpmap:97 AMR/8000/1 a=fmtp:97 mode-change-capability=2; max-red=220 a=rtpmap:98 AMR/8000/1 a=fmtp:98 mode-change-capability=2; max-red=220; octet-align=1 a=ecn-capable-rtp: leap ect=0 a=ptime:20 a=maxptime:240 |
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SDP answer |
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m=audio 49152 RTP/AVP 99 b=AS:29 b=RS:0 b=RR:0 a=rtpmap:99 AMR/8000/1 a=fmtp:99 mode-change-capability=2; max-red=220 a=ecn-capable-rtp: leap ect=0 a=ptime:20 a=maxptime:240 |
Comments:
The SDP offer includes the SDP attribute ‘ecn-capable-rtp’ to indicate that ECN is supported. The SDP offer further includes the parameters: ‘leap’ to indicate that the leap-of-faith initiation method is to be used; and ‘ect=0’ to request that the other endpoint sets the ECN bits to ECT(0). The SDP offer does not include the "rtcp-fb" attribute for negotiating use of the RTCP AVPF ECN feedback messages [84]. This results in RTP CMR [28] being used as the application specific feedback for ECN-triggered adaptation. The SDP offer also proposes to not use RTCP for the session.
The SDP answer is configured in the same way as in the offer to indicate that the ECN usage and its configuration is agreeable to be used in the session.
A.12.1.2 With RTP/AVPF and non-zero RTCP bandwidth
This SDP example is based on the SDP example found in Table A.3.0 except that bandwidth information for the media has been added. The negotiation of Reduced-Size RTCP is added together with the ECN negotiation. Non-zero RTCP bandwidth and AVPF have also been negotiated.
Table A.12.1.2: SDP example
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SDP offer |
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m=audio 49152 RTP/AVP 97 98 a=tcap:1 RTP/AVPF a=pcfg:1 t=1 b=AS:30 b=RS:0 b=RR:2000 a=rtpmap:97 AMR/8000/1 a=fmtp:97 mode-change-capability=2; max-red=220 a=rtpmap:98 AMR/8000/1 a=fmtp:98 mode-change-capability=2; max-red=220; octet-align=1 a=ecn-capable-rtp: leap ect=0 a=rtcp-rsize a=ptime:20 a=maxptime:240 |
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SDP answer |
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m=audio 49152 RTP/AVPF 99 a=acfg:1 t=1 b=AS:29 b=RS:0 b=RR:2000 a=rtpmap:99 AMR/8000/1 a=fmtp:99 mode-change-capability=2; max-red=220 a=ecn-capable-rtp: leap ect=0 a=rtcp-rsize a=ptime:20 a=maxptime:240 |
Comments:
The SDP offer includes the SDP attribute ‘ecn-capable-rtp’ to indicate that ECN is supported. The SDP offer further includes the parameters: ‘leap’ to indicate that the leap-of-faith initiation method is to be used; and ‘ect=0’ to request that the other endpoint sets the ECN bits to ECT(0). The SDP offer does not include the "rtcp-fb" attribute for negotiating use of the RTCP AVPF ECN feedback messages [84]. This results in RTCP-APP CMR and reduced-size RTCP being used as the application specific feedback for ECN-related adaptation.
The SDP answer is configured in the same way as in the offer to indicate that the ECN usage and its configuration is agreeable to be used in the session.
A.12.1.3 With RTCP ECN feedback messages and RTCP XR ECN summary reports for inter-working with non-MTSI clients
The following SDP offer and SDP answer are possible when an MTSI client is inter-working with non-MTSI clients and when the MTSI client supports RTCP AVPF ECN feedback messages and RTCP XR ECN summary reports.
Table A.12.1.3: SDP example
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SDP offer |
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m=audio 49152 RTP/AVP 97 98 a=tcap:1 RTP/AVPF a=pcfg:1 t=1 b=AS:30 b=RS:0 b=RR:2000 a=rtpmap:97 AMR/8000/1 a=fmtp:97 mode-change-capability=2; max-red=220 a=rtpmap:98 AMR/8000/1 a=fmtp:98 mode-change-capability=2; max-red=220; octet-align=1 a=ecn-capable-rtp: leap ect=0 a=rtcp-fb:* nack ecn a=rtcp-xr:ecn-sum a=rtcp-rsize a=ptime:20 a=maxptime:240 |
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SDP answer |
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m=audio 49152 RTP/AVPF 99 a=acfg:1 t=1 b=AS:29 b=RS:0 b=RR:2000 a=rtpmap:99 AMR/8000/1 a=fmtp:99 mode-change-capability=2; max-red=220 a=ecn-capable-rtp: leap ect=0 a=rtcp-fb:* nack ecn a=rtcp-xr:ecn-sum a=rtcp-rsize a=ptime:20 a=maxptime:240 |
Comments:
The SDP offer is similar to the offer in Table A.12.2. The line "a=rtcp-fb:* nack ecn" is included to indicate that the RTCP AVPF ECN feedback messages can be used by all payload types for speech. The line "a=rtcp-xr:ecn-sum" is included to indicate that the RTCP XR ECN summary reports can also be used.
Since the offering MTSI client supports the RTCP AVPF ECN feedback messages and RTCP XR ECN summary reports there is no need to insert any media gateway in the path to solve inter-working.
A.12.2 SDP examples when using ECN for video in RTP
A.12.2.1 Without RTCP AVPF ECN feedback messages and RTCP XR ECN summary reports
The following SDP offer and SDP answer are likely when both MTSI clients in terminals use ECN for video and TMMBR for rate adaptation.
This SDP example is the same as the SDP example found in Tables A.4.4b and A.4.4c, except that the negotiation for ECN has been added.
Table A.12.2.1: Example SDP offer for H.264 video with ECN
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SDP offer |
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m=video 49154 RTP/AVP 99 a=tcap:1 RTP/AVPF a=pcfg:1 t=1 b=AS:315 b=RS:0 b=RR:2500 a=rtpmap:99 H264/90000 a=fmtp:99 packetization-mode=0;profile-level-id=42e00a; \ sprop-parameter-sets=J0LgCpWgsToB/UA=,KM4Gag== a=rtcp-fb:* trr-int 5000 a=rtcp-fb:* nack a=rtcp-fb:* nack pli a=rtcp-fb:* ccm tmmbr a=rtcp-fb:* ccm fir a=ecn-capable-rtp: leap ect=0 a=extmap:4 urn:3gpp:video-orientation |
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SDP answer |
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m=video 49154 RTP/AVPF 99 a=acfg:1 t=1 b=AS:315 b=RS:0 b=RR:2500 a=rtpmap:99 H264/90000 a=fmtp:99 packetization-mode=0;profile-level-id=42e00a; \ sprop-parameter-sets=J0LgCpWgsToB/UA=,KM4Gag== a=rtcp-fb:* trr-int 5000 a=rtcp-fb:* nack a=rtcp-fb:* nack pli a=rtcp-fb:* ccm tmmbr a=rtcp-fb:* ccm fir a=ecn-capable-rtp: leap ect=0 a=extmap:4 urn:3gpp:video-orientation |
Comments:
The SDP offer includes the SDP attribute ‘ecn-capable-rtp’ to indicate that ECN is supported. The SDP offer further includes the parameters: ‘leap’ to indicate that the leap-of-faith initiation method is to be used; and ‘ect=0’ to request that the other endpoint sets the ECN bits to ECT(0).
The SDP offer also includes an offer for AVPF to enable sending adaptation requests without following the normal rules for RTCP transmission intervals. TMMBR is also offered to indicate that this can be used for rate adaptation.
The SDP answer is configured in the same way as in the offer to indicate that the ECN usage and its configuration is agreeable to be used in the session.
A.12.2.2 With RTCP AVPF ECN feedback messages and RTCP XR ECN summary reports for inter-working with non-MTSI clients
The following SDP offer and SDP answer are possible when an MTSI client is inter-working with non-MTSI clients not supporting TMMBR and when the MTSI client supports RTCP AVPF ECN feedback messages and RTCP XR ECN summary reports.
This SDP example is the same as the SDP example found in Tables A.4.4b and A.4.4c, except that the negotiation for ECN has been added.
Table A.12.2.2: Example SDP offer for H.264 video with ECN
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SDP offer |
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m=video 49154 RTP/AVP 99 a=tcap:1 RTP/AVPF a=pcfg:1 t=1 b=AS:315 b=RS:0 b=RR:2500 a=rtpmap:99 H264/90000 a=fmtp:99 packetization-mode=0;profile-level-id=42e00a; \ sprop-parameter-sets=J0LgCpWgsToB/UA=,KM4Gag== a=ecn-capable-rtp: leap ect=0 a=rtcp-fb:* trr-int 5000 a=rtcp-fb:* nack a=rtcp-fb:* nack pli a=rtcp-fb:* ccm tmmbr a=rtcp-fb:* ccm fir a=rtcp-fb:* nack ecn a=rtcp-xr:ecn-sum a=extmap:4 urn:3gpp:video-orientation |
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SDP answer (non-MTSI client) |
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m=video 49154 RTP/AVPF 99 a=acfg:1 t=1 b=AS:315 b=RS:0 b=RR:2500 a=rtpmap:99 H264/90000 a=fmtp:99 packetization-mode=0;profile-level-id=42e00a; \ sprop-parameter-sets=J0LgCpWgsToB/UA=,KM4Gag== a=ecn-capable-rtp: leap ect=0 a=rtcp-fb:* trr-int 5000 a=rtcp-fb:* nack a=rtcp-fb:* nack pli a=rtcp-fb:* nack ecn a=rtcp-xr:ecn-sum a=extmap:4 urn:3gpp:video-orientation |
Comments:
The SDP offer is similar to the offer in Table A.12.2.1. The line "a=rtcp-fb:* nack ecn" is included to indicate that the RTCP AVPF ECN feedback messages can be used all payload types for video. The line "a=rtcp-xr:ecn-sum" is included to indicate that the RTCP XR ECN summary reports can also be used.
The answering client does not support TMMBR and full intra requests and therefore removes these attribute lines when creating the SDP answer.
Since the offering MTSI client supports the RTCP AVPF ECN feedback messages and RTCP XR ECN summary reports there is no need to insert any media gateway in the path to provide inter-working.