A Transport Independent Bandwidth Modifier for the Session Description Protocol (SDP)
RFC 3890

Network Working Group                                      M. Westerlund
Request for Comments: 3890                                      Ericsson
Category: Standards Track                                 September 2004

              A Transport Independent Bandwidth Modifier
               for the Session Description Protocol (SDP)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document defines a Session Description Protocol (SDP) Transport
   Independent Application Specific Maximum (TIAS) bandwidth modifier
   that does not include transport overhead; instead an additional
   packet rate attribute is defined.  The transport independent bit-rate
   value together with the maximum packet rate can then be used to
   calculate the real bit-rate over the transport actually used.

   The existing SDP bandwidth modifiers and their values include the
   bandwidth needed for the transport and IP layers.  When using SDP
   with protocols like the Session Announcement Protocol (SAP), the
   Session Initiation Protocol (SIP), and the Real-Time Streaming
   Protocol (RTSP), and when the involved hosts has different transport
   overhead, for example due to different IP versions, the
   interpretation of what lower layer bandwidths are included is not
   clear.

Westerlund                  Standards Track                     [Page 1]
RFC 3890               Bandwidth Modifier for SDP         September 2004

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.  The Bandwidth Attribute. . . . . . . . . . . . . . . . .  3
             1.1.1.  Conference Total . . . . . . . . . . . . . . . .  3
             1.1.2.  Application Specific Maximum . . . . . . . . . .  3
             1.1.3.  RTCP Report Bandwidth. . . . . . . . . . . . . .  4
       1.2.  IPv6 and IPv4. . . . . . . . . . . . . . . . . . . . . .  4
       1.3.  Further Mechanisms that Change the Bandwidth
             Utilization. . . . . . . . . . . . . . . . . . . . . . .  5
             1.3.1.  IPsec. . . . . . . . . . . . . . . . . . . . . .  5
             1.3.2.  Header Compression . . . . . . . . . . . . . . .  5
   2.  Definitions. . . . . . . . . . . . . . . . . . . . . . . . . .  6
       2.1.  Glossary . . . . . . . . . . . . . . . . . . . . . . . .  6
       2.2.  Terminology. . . . . . . . . . . . . . . . . . . . . . .  6
   3.  The Bandwidth Signaling Problems . . . . . . . . . . . . . . .  6
       3.1.  What IP Version is Used. . . . . . . . . . . . . . . . .  6
       3.2.  Taking Other Mechanisms into Account . . . . . . . . . .  7
       3.3.  Converting Bandwidth Values. . . . . . . . . . . . . . .  8
       3.4.  RTCP Problems. . . . . . . . . . . . . . . . . . . . . .  8
       3.5.  Future Development . . . . . . . . . . . . . . . . . . .  9
       3.6.  Problem Conclusion . . . . . . . . . . . . . . . . . . .  9
   4.  Problem Scope. . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 10
   6.  Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
       6.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . 11
       6.2.  The TIAS Bandwidth Modifier. . . . . . . . . . . . . . . 11
             6.2.1.  Usage. . . . . . . . . . . . . . . . . . . . . . 11
             6.2.2.  Definition . . . . . . . . . . . . . . . . . . . 12
             6.2.3.  Usage Rules. . . . . . . . . . . . . . . . . . . 13
       6.3.  Packet Rate Parameter. . . . . . . . . . . . . . . . . . 13
       6.4.  Converting to Transport-Dependent Values . . . . . . . . 14
       6.5.  Deriving RTCP bandwidth. . . . . . . . . . . . . . . . . 15
             6.5.1. Motivation for this Solution. . . . . . . . . . . 15
       6.6.  ABNF Definitions . . . . . . . . . . . . . . . . . . . . 16
       6.7.  Example. . . . . . . . . . . . . . . . . . . . . . . . . 16
   7.  Protocol Interaction . . . . . . . . . . . . . . . . . . . . . 17
       7.1.  RTSP . . . . . . . . . . . . . . . . . . . . . . . . . . 17
       7.2.  SIP. . . . . . . . . . . . . . . . . . . . . . . . . . . 17
       7.3.  SAP. . . . . . . . . . . . . . . . . . . . . . . . . . . 18
   8.  Security Considerations. . . . . . . . . . . . . . . . . . . . 18
   9.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 18
   10. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 19
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19