Network Working Group H. Schulzrinne
Request for Comments: 3550 Columbia University
Obsoletes: 1889 S. Casner
Category: Standards Track Packet Design
R. Frederick
Blue Coat Systems Inc.
V. Jacobson
Packet Design
July 2003
RTP: A Transport Protocol for Real-Time Applications
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 memorandum describes RTP, the real-time transport protocol. RTP
provides end-to-end network transport functions suitable for
applications transmitting real-time data, such as audio, video or
simulation data, over multicast or unicast network services. RTP
does not address resource reservation and does not guarantee
quality-of-service for real-time services. The data transport is
augmented by a control protocol (RTCP) to allow monitoring of the
data delivery in a manner scalable to large multicast networks, and
to provide minimal control and identification functionality. RTP and
RTCP are designed to be independent of the underlying transport and
network layers. The protocol supports the use of RTP-level
translators and mixers.
Most of the text in this memorandum is identical to RFC 1889 which it
obsoletes. There are no changes in the packet formats on the wire,
only changes to the rules and algorithms governing how the protocol
is used. The biggest change is an enhancement to the scalable timer
algorithm for calculating when to send RTCP packets in order to
minimize transmission in excess of the intended rate when many
participants join a session simultaneously.
Schulzrinne, et al. Standards Track [Page 1]
RFC 3550 RTP July 2003
Table of Contents
1. Introduction ................................................ 4
1.1 Terminology ............................................ 5
2. RTP Use Scenarios ........................................... 5
2.1 Simple Multicast Audio Conference ...................... 6
2.2 Audio and Video Conference ............................. 7
2.3 Mixers and Translators ................................. 7
2.4 Layered Encodings ...................................... 8
3. Definitions ................................................. 8
4. Byte Order, Alignment, and Time Format ...................... 12
5. RTP Data Transfer Protocol .................................. 13
5.1 RTP Fixed Header Fields ................................ 13
5.2 Multiplexing RTP Sessions .............................. 16
5.3 Profile-Specific Modifications to the RTP Header ....... 18
5.3.1 RTP Header Extension ............................ 18
6. RTP Control Protocol -- RTCP ................................ 19
6.1 RTCP Packet Format ..................................... 21
6.2 RTCP Transmission Interval ............................. 24
6.2.1 Maintaining the Number of Session Members ....... 28
6.3 RTCP Packet Send and Receive Rules ..................... 28
6.3.1 Computing the RTCP Transmission Interval ........ 29
6.3.2 Initialization .................................. 30
6.3.3 Receiving an RTP or Non-BYE RTCP Packet ......... 31
6.3.4 Receiving an RTCP BYE Packet .................... 31
6.3.5 Timing Out an SSRC .............................. 32
6.3.6 Expiration of Transmission Timer ................ 32
6.3.7 Transmitting a BYE Packet ....................... 33
6.3.8 Updating we_sent ................................ 34
6.3.9 Allocation of Source Description Bandwidth ...... 34
6.4 Sender and Receiver Reports ............................ 35
6.4.1 SR: Sender Report RTCP Packet ................... 36
6.4.2 RR: Receiver Report RTCP Packet ................. 42
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