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Network Working Group Request for Comments: 1889 Category: Standards Track

Audio-Video Transport Working Group H. Schulzrinne GMD Fokus S. Casner Precept Software, Inc. R. Frederick Xerox Palo Alto Research Center V. Jacobson Lawrence Berkeley National Laboratory January 1996

RTP: A Transport Protocol for Real-Time Applications Status of this Memo This document specifies an Internetstandards 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. Abstract This memorandum describes RTP, the real-time transport protocol. RTP provides end-to-end networktransport 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-ofservice 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 largemulticast 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. Table of Contents 1. 2. 2.1 2.2 2.3 3. 4. 5. 5.1 5.2 Introduction ........................................ RTP Use Scenarios................................... Simple Multicast Audio Conference ................... Audio and Video Conference .......................... Mixers and Translators .............................. Definitions ......................................... Byte Order, Alignment, and Time Format .............. RTP Data Transfer Protocol .......................... RTP Fixed Header Fields ............................. Multiplexing RTPSessions ........................... 3 5 5 6 6 7 9 10 10 13

Schulzrinne, et al

Standards Track

[Page 1]

RFC 1889

RTP

January 1996

5.3 5.3.1 6. 6.1 6.2 6.2.1 6.2.2 6.3 6.3.1 6.3.2 6.3.3 6.3.4 6.4 6.4.1 6.4.2 6.4.3 6.4.4 6.4.5 6.4.6 6.4.7 6.4.8 6.5 6.6 7. 7.1 7.2 7.3 7.4 8. 8.1 8.2 9. 9.1 9.2 10. 11. 11.1 11.2 12. A. A.1 A.2 A.3 A.4 A.5 A.6 A.7

Profile-Specific Modificationsto the RTP Header..... RTP Header Extension ................................ RTP Control Protocol -- RTCP ........................ RTCP Packet Format .................................. RTCP Transmission Interval .......................... Maintaining the number of session members ........... Allocation of source description bandwidth .......... Sender and Receiver Reports .........................SR: Sender report RTCP packet ....................... RR: Receiver report RTCP packet ..................... Extending the sender and receiver reports ........... Analyzing sender and receiver reports ............... SDES: Source description RTCP packet ................ CNAME: Canonical end-point identifier SDES item ..... NAME: User name SDES item ........................... EMAIL: Electronic mailaddress SDES item ............ PHONE: Phone number SDES item ....................... LOC: Geographic user location SDES item ............. TOOL: Application or tool name SDES item ............ NOTE: Notice/status SDES item ....................... PRIV: Private extensions SDES item .................. BYE: Goodbye RTCP packet ............................ APP: Application-defined RTCP packet................ RTP Translators and Mixers .......................... General Description ................................. RTCP Processing in Translators ...................... RTCP Processing in Mixers ........................... Cascaded Mixers ..................................... SSRC Identifier Allocation and Use .................. Probability of Collision ............................ Collision...