Using Simulcast in Session Description Protocol (SDP) and RTP Sessions
RFC 8853
| Document | Type | RFC - Proposed Standard (January 2021; No errata) | |
|---|---|---|---|
| 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)
|
||
| 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
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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 can
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