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Transport Independent SDP Bandwidth Parameter

This draft proposes a solution to address the limitations of the SDP bandwidth modifier in signaling bandwidth in various protocols. It introduces a transport-independent version of the bandwidth modifier and defines attributes for maximum packet rate. The draft also suggests default behavior for RTCP to ensure equal send rates. The way forward includes considering these issues in SDP-NG and addressing the requirements of different services running over NAT-PTs.

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Transport Independent SDP Bandwidth Parameter

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  1. Transport Independent SDP Bandwidth Parameter Draft-westerlund-mmusic-sdp-bwparam-01.txt Author: Magnus Westerlund

  2. Outline • The Problem • A Solution • The Way Forward • Open Issues

  3. The Problem (1 of 2) • The most commonly used SDP bandwidth modifier is AS:Application specific maximum. • SDP and “b=“ is used to signal bandwidth in SIP, SAP, and RTSP. • Usage of NAT-PT (Network Address Translation – Protocol Translation) as an IPv4 to IPv6 transition mechanism does not work for “b=AS”. • Other mechanisms altering the overhead are also problematic to take into consideration.

  4. The Problem (2 of 2) • In some cases it is impossible to know which IP version that is included in AS. • The packet rate is required for conversions.

  5. A Solution • Define a transport independent version of the AS bandwidth modifier (TIAS), i.e. only payload bitrate. • Define attributes for maximum packet rate (a=maxprate) • The maximum bandwidth over a link can then be calculated as: BW = TIAS + maxprate*size(IP/UDP/RTP) • Define default behavior for RTCP that will give all participants equal send rate, although not equal bit rate.

  6. The Way Forward • Intended as a simple and quick fix that can be used until SDP-NG becomes available. • SDP-NG must consider the problems in more detail. • Is needed for different services that will run over NAT-PTs. For example 3GPP’s Packet-based Streaming Service needs accurate bandwidth modifiers for radio resource allocation and to determine if a session can be supported. • To meet the 3GPP deadlines, an RFC is needed June 2003. Target: WG Last call in January. • New version before Christmas.

  7. Open Issues • May this work become a MMUSIC Work Group Item? • Is there any need at all for average packet rates? • Usage of TIAS on session level? • Is the RTCP solution satisfactory? • Influence the draft-ietf-avt-rtcp-bw-05.txt? • Protocol Interactions need review!

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