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Enhanced SDP Media Alignment in SIP: Addressing Diverse Encoding Scenarios

This document outlines the proposal for improved SDP media alignment in SIP, focusing on scenarios involving variations in media encoding and transport. It highlights the need for systems to accommodate media streams encoded in different formats and accessed through various ports and interfaces. The proposal introduces a flow identification mechanism to simplify encoding management, facilitating better interoperability with third-party RTP libraries and transcoding points. Concrete examples illustrate the concept, demonstrating how different codecs can coexist within a single session.

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Enhanced SDP Media Alignment in SIP: Addressing Diverse Encoding Scenarios

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  1. SDP media alignment in SIP draft-camarillo-sip-sdp-00.txt Gonzalo Camarillo Gonzalo.Camarillo@ericsson.com

  2. Outline • What is needed? • Scenarios • Cellular access • 3rd party developed RTP libraries • Transcoding point • Proposal: Flow identification

  3. What is needed? • Systems have to be able to receive media from a single media stream, encoded in different formats during the session, in different ports and host interfaces. • Better method to perform SDP media alignment in SIP than matching the nth lines.

  4. Cellular Access RAB 1 RAB 2 Packet filter (TFT) RAB 3 INVITE contains different port numbers for different codecs

  5. 3rd party developed RTP libraries SIP User Agent Interface Interface RTP library supporting PCM and GSM RTP library supporting AMR UDP 20000 UDP 20010 INVITE contains different port numbers for different codecs

  6. Transcoding point Cellular Wired infrastructure Wired infrastructure Transcoding point Wired infrastructure INVITE contains different IP addresses for different codecs

  7. Proposal • SDP session parameter: Flow Identifier (fid) • Example: v=0 o=Laura 289083124 289083124 IN IP4 second.example.com t=0 0 c=IN IP4 222.222.222.222 m=audio 30000 RTP/AVP 0 a=fid:1 m=audio 30002 RTP/AVP 8 c=IN IP4 123.123.123.123 a=fid:1 m=audio 30004 RTP/AVP 0 a=fid:2 m=audio 30006 RTP/AVP 8 c=IN IP4 123.123.123.123 a=fid:2

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