Internet DRAFT - draft-hdesinen-mmusic-oa-send-bw-attr

draft-hdesinen-mmusic-oa-send-bw-attr





Network Working Group                                        H. Desineni
Internet-Draft                                                  N. Leung
Intended status: Standards Track                                Qualcomm
Expires: August 27, 2007                               February 23, 2007


           'MSR' Bandwidth modifier in SDP Offer/Answer model
              draft-hdesinen-mmusic-oa-send-bw-attr-02.txt

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   Copyright (C) The IETF Trust (2007).














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Abstract

   This document defines a new SDP bandwidth modifier that can be used
   to specify the maximum media bitrate in 'send' direction of a stream
   in SDP offer/answer model.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Use case . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  The MSR Bandwidth Modifier . . . . . . . . . . . . . . . . . .  7
     5.1.  Definition . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.2.  Usage Rules  . . . . . . . . . . . . . . . . . . . . . . .  7
     5.3.  ABNF Definition  . . . . . . . . . . . . . . . . . . . . .  7
   6.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 13


























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1.  Introduction

   RFC 3264 defines the SDP Offer/answer model for unicast multimedia
   sessions where information from both participants is needed for the
   complete view of the session.  According to RFC 3264, bandwidth
   attribute present in the SDP offer signals the desired bandwidth that
   the offerer would like to receive.  Hence, bandwidth attributes "AS"
   and "TIAS" defined in RFC 3550 and RFC 3890 respectively can only be
   used as receive-only attributes in SDP offer/answer model.  A stream
   receiver (Offerer or Answerer) signals the value of "TIAS" based on
   maximum media bitrate it desires to receive.  The stream sender
   (Answerer or Offerer) may send media at a maximum bitrate much lower
   than "TIAS".  Knowing the sender's (smaller) maximum media bitrate
   enables better resource allocation.





































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2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].














































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3.  Background

   Section 5.8 of RFC 4566 defines the syntax for "b=" bandwidth
   attribute.  It also defines the bandwidth type "AS" as application's
   concept of maximum bandwidth.

   According to section 6.2 of RFC 3550, for RTP based applications,
   "AS" includes the header overhead due to lower layer transport and
   network protocols (e.g., UDP, IP ) and does not include the overhead
   due to link level headers.

   Section 6.2 of RFC 3890 defines the bandwidth type "TIAS".  In the
   context of RTP transport, "TIAS" provides the bandwidth for RTP
   payload which includes payload format header and payload data.
   "TIAS" does not include any other layer overhead including RTP layer.

   According to RFC3264, any bandwidth attribute present in an SDP offer
   signals the desired bandwidth that the offerer would like to receive.
   Hence, bandwidth attributes "AS" and "TIAS" defined in RFC 3550 and
   RFC 3890 respectively can only be used as receive-only attributes in
   SDP offer/answer model.






























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4.  Use case

   In SDP offer/answer model, the answerer's send bitrate for the stream
   in answerer->offerer direction depends on the value of "AS" or "TIAS"
   signaled in the SDP offer.  The answerer may send media at a bit-rate
   much lower than "AS" or "TIAS" signaled by the offerer.  This could
   be due to several reasons including QoS resource limitation over the
   answerer's first hop link.  Similarly, offerer's send bitrate for the
   stream in offerer->answerer direction may be much lower than "AS" or
   "TIAS" signaled in the SDP answer.

   Cellular links commonly have some type of QoS negotiation enabling
   the cellular device to learn the maximum bitrate available over the
   first hop link.  Signaling the maximum media send bitrate to the
   receiving device can be beneficial to allocate proper QoS resources
   over the last hop link.  This is especially beneficial in preventing
   resource overallocation when the last hop is a cellular link.

   Bandwidth inequality over first and last hop links can also arise
   when the offerer and answerer are attached to different types of
   networks.  E.g., Offerer is a cellular device and answerer is a PC
   phone with wireline connection.

   The 'MSR' bandwidth modifier defined in the following section can be
   used to specify the maximum media bitrate in 'send' direction of a
   stream.  For an example usage, see Section 6.

























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5.  The MSR Bandwidth Modifier

5.1.  Definition

   MSR bandwidth modifier is defined as shown below:

   b=MSR: <bandwidth-value> ; see [7] for ABNF definition.

   The Maximum Send Rate (MSR) bandwidth modifier specifies the maximum
   media bitrate in 'send' direction of a stream in SDP offer/answer
   model.  'MSR' has an integer bit-rate value in bits per second.  A
   fractional bandwidth value SHALL always be rounded up to the next
   integer.  The bandwidth value is the maximum bit-rate without
   counting the protocol header bytes from IP or other transport layers
   like TCP,UDP and RTP.

5.2.  Usage Rules

   'MSR' bandwidth modifier is intended to be used only at the SDP media
   level.  It MUST not be used with a 'recvonly' stream.

5.3.  ABNF Definition

   The bandwidth modifier:

   MSR-bandwidth-def = "b" "=" "MSR" ":" bandwidth-value CRLF

   bandwidth-value = 1*DIGIT























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6.  Example

   Alice offers a receive only stream to Bob with maximum receive media
   bitrate ("TIAS") 128000bps (H.263 profile 0 level 45).  Bob responds
   with SDP answer by marking the stream as sendonly.  Note that the SDP
   answer from Bob does not include any bandwidth attribute as it
   contains a sendonly stream.


   [Offer from Alice]
   m=video 34564 RTP/AVP 96
   a=rtpmap:96 h263-1998/90000
   a=fmtp:96 profile=0; level=45;
   b=TIAS:128000
   a=maxprate:20
   a=recvonly


   [Answer from Bob]
   m=video 46236 RTP/AVP 96
   a=rtpmap:96 h263-1998/90000
   a=fmtp:96 profile=0;level=45;
   a=sendonly

   Due to QoS limitation on its first hop link, Bob can send media at
   maximum bitrate of 64000bps only.  Unaware of Bob's maximum media
   bitrate, Alice overallocates QoS resources on its access (last hop)
   link.  Signaling Bob's maximum media bitrate in the SDP answer can
   help Alice reserve correct QoS resources in its access (last hop)
   link.  The complete offer/answer example with proposed bandwidth
   attribute 'MSR' is shown below.


   [Offer from Alice]
   m=video 34564 RTP/AVP 96
   a=rtpmap:96 h263-1998/90000
   a=fmtp:96 profile=0; level=45;
   b=TIAS:128000
   a=maxprate:20
   a=recvonly


   [Answer from Bob]
   m=video 46236 RTP/AVP 96
   a=rtpmap:96 h263-1998/90000
   a=fmtp:96 profile=0;level=45;
   b=MSR:64000
   a=sendonly



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7.  Security Considerations

   [TBD]
















































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8.  IANA Considerations

   [TBD]
















































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9.  References

9.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [2]   Schulzrinne, H., "RTP: A Transport Protocol for Real-Time
         Applications", STD 64, RFC 3550, March 1997.

   [3]   Rosenberg, J., "An Offer/Answer Model with Session Description
         Protocol (SDP)", RFC 3264, June 2002.

   [4]   Narten, T., "Guidelines for Writing an IANA Considerations
         Section in RFCs", RFC 2434, October 1998.

   [5]   Handley, M., "SDP: Session Description Protocol", RFC 4566,
         July 2006.

   [6]   Westerlund, M., "A Transport Independent Bandwidth Modifier for
         the Session Description Protocol (SDP)", RFC 3890,
         September 2004.

   [7]   Crocker, C., "Augmented BNF for Syntax Specifications: ABNF",
         RFC 2234, November 1997.

9.2.  Informative References

   [8]   Schulzrinne, H., "RTP Profile for Audio and Video Conferences
         with Minimal Control", STD 65, RFC 3551, July 2003.

   [9]   Schulzrinne, H., "Real Time Streaming Protocol (RTSP)",
         RFC 2326, April 1998.

   [10]  Johnston, A., "SDP Offer/Answer Examples", RFC 4317,
         December 2005.

   [11]  Westerlund, M., "How to Write an RTP Payload Format",
         draft-ietf-avt-rtp-howto-00.txt(Work in Progress) , May 2006.












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Authors' Addresses

   Harikishan Desineni
   Qualcomm
   5775 Morehouse Drive
   San Diego, CA  92126
   USA

   Phone: +1 858 845 8996
   Email: hd@qualcomm.com
   URI:   http://www.qualcomm.com


   Nikolai Leung
   Qualcomm
   7710 Takoma Ave
   Takoma Park, MD  20912
   USA

   Phone: +1 858 845 3333
   Email: nleung@qualcomm.com
   URI:   http://www.qualcomm.com





























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