Using Simulcast in Session Description Protocol (SDP) and RTP Sessions
RFC 8853
Document | Type | RFC - Proposed Standard (January 2021; No errata) | |
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Authors | Bo Burman , Magnus Westerlund , Suhas Nandakumar , Mo Zanaty | ||
Last updated | 2021-01-19 | ||
Replaces | draft-burman-mmusic-sdp-simulcast | ||
Stream | Internet Engineering Task Force (IETF) | ||
Formats | plain text html xml pdf htmlized (tools) htmlized bibtex | ||
Reviews | |||
Stream | WG state | Submitted to IESG for Publication | |
Document shepherd | Flemming Andreasen | ||
Shepherd write-up | Show (last changed 2018-03-06) | ||
IESG | IESG state | RFC 8853 (Proposed Standard) | |
Action Holders |
(None)
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Consensus Boilerplate | Yes | ||
Telechat date | |||
Responsible AD | Ben Campbell | ||
Send notices to | (None) | ||
IANA | IANA review state | Version Changed - Review Needed | |
IANA action state | RFC-Ed-Ack |
Internet Engineering Task Force (IETF) B. Burman Request for Comments: 8853 M. Westerlund Category: Standards Track Ericsson ISSN: 2070-1721 S. Nandakumar M. Zanaty Cisco January 2021 Using Simulcast in Session Description Protocol (SDP) and RTP Sessions Abstract In some application scenarios, it may be desirable to send multiple differently encoded versions of the same media source in different RTP streams. This is called simulcast. This document describes how to accomplish simulcast in RTP and how to signal it in the Session Description Protocol (SDP). The described solution uses an RTP/RTCP identification method to identify RTP streams belonging to the same media source and makes an extension to SDP to indicate that those RTP streams are different simulcast formats of that media source. The SDP extension consists of a new media-level SDP attribute that expresses capability to send and/or receive simulcast RTP streams. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8853. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction 2. Definitions 2.1. Terminology 2.2. Requirements Language 3. Use Cases 3.1. Reaching a Diverse Set of Receivers 3.2. Application-Specific Media Source Handling 3.3. Receiver Media-Source Preferences 4. Overview 5. Detailed Description 5.1. Simulcast Attribute 5.2. Simulcast Capability 5.3. Offer/Answer Use 5.3.1. Generating the Initial SDP Offer 5.3.2. Creating the SDP Answer 5.3.3. Offerer Processing the SDP Answer 5.3.4. Modifying the Session 5.4. Use with Declarative SDP 5.5. Relating Simulcast Streams 5.6. Signaling Examples 5.6.1. Single-Source Client 5.6.2. Multisource Client 5.6.3. Simulcast and Redundancy 6. RTP Aspects 6.1. Outgoing from Endpoint with Media Source 6.2. RTP Middlebox to Receiver 6.2.1. Media-Switching Mixer 6.2.2. Selective Forwarding Middlebox 6.3. RTP Middlebox to RTP Middlebox 7. Network Aspects 7.1. Bitrate Adaptation 8. Limitation 9. IANA Considerations 10. Security Considerations 11. References 11.1. Normative References 11.2. Informative References Appendix A. Requirements Acknowledgements Contributors Authors' Addresses 1. Introduction Most of today's multiparty video-conference solutions make use of centralized servers to reduce the bandwidth and CPU consumption in the endpoints. Those servers receive RTP streams from each participant and send some suitable set of possibly modified RTP streams to the rest of the participants, which usually have heterogeneous capabilities (screen size, CPU, bandwidth, codec, etc.). One of the biggest issues is how to perform RTP stream adaptation to different participants' constraints with the minimum possible impact on both video quality and server performance. Simulcast is defined in this memo as the act of simultaneously sending multiple different encoded streams of the same media source -- e.g., the same video source encoded with different video-encoder types or image resolutions. This can be done in several ways and for different purposes. This document focuses on the case where it is desirable to provide a media source as multiple encoded streams over RTP [RFC3550] towards an intermediary so that the intermediary canShow full document text