RFC 3556 (rfc3556) - Page 1 of 8


Session Description Protocol (SDP) Bandwidth Modifiers for RTP Control Protocol (RTCP) Bandwidth



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Network Working Group                                          S. Casner
Request for Comments: 3556                                 Packet Design
Category: Standards Track                                      July 2003


         Session Description Protocol (SDP) Bandwidth Modifiers
               for RTP Control Protocol (RTCP) Bandwidth

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 (2003).  All Rights Reserved.

Abstract

   This document defines an extension to the Session Description
   Protocol (SDP) to specify two additional modifiers for the bandwidth
   attribute.  These modifiers may be used to specify the bandwidth
   allowed for RTP Control Protocol (RTCP) packets in a Real-time
   Transport Protocol (RTP) session.

1.  Introduction

   The Real-time Transport Protocol (RTP), RFC 3550 [1], includes a
   control protocol RTCP which provides synchronization information from
   data senders and feedback information from data receivers.

   Normally, the amount of bandwidth allocated to RTCP in an RTP session
   is 5% of the session bandwidth.  For some applications, it may be
   appropriate to specify the RTCP bandwidth independently of the
   session bandwidth.  Using a separate parameter allows rate-adaptive
   applications to set an RTCP bandwidth consistent with a "typical"
   data bandwidth that is lower than the maximum bandwidth specified by
   the session bandwidth parameter.  That allows the RTCP bandwidth to
   be kept under 5% of the data bandwidth when the rate has been adapted
   downward.

   On the other hand, there may be applications that send data at very
   low rates but need to communicate extra RTCP information, such as APP
   packets.  These applications may need to specify RTCP bandwidth that
   is higher than 5% of the data bandwidth.



Casner                      Standards Track


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