Indicating Exclusive Support of RTP/RTCP Multiplexing using SDP
draft-holmberg-mmusic-mux-exclusive-00

Abstract

This document defines how an endpoint can indicate exclusive support of RTP/RTCP multiplexing using the Session Description Protocol (SDP).

The document updates RFC 5761, by defining how the SDP 'rtcp' attribute is used, together with the SDP 'rtcp-mux' attribute, to indicate exclusive support of RTP/RTCP multiplexing.

Editor's note: 'exclusive' is probably not the best terminology, so feel free to suggest something more appropriate.

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Table of Contents

• 1. Introduction
• 2. Conventions
• 3. SDP Offer/Answer Considerations
• 4. Update to RFC 5761
• 4.1. General
• 4.2. RFC 5761 Section 5.1.1 Update
• 4.3. Issues And TBDs
• 5. Security Considerations
• 6. IANA Considerations
• 7. Acknowledgments
• 8. Change Log
• 9. Normative References
• Author's Address

1. Introduction

[RFC5761] defines how to multiplex RTP and RTCP on a single port, referred to as RTP/RTCP multiplexing. [RFC5761] also defines an Session Description Protocol (SDP) [RFC4566] attribute, 'rtcp-mux' that can be used by entities to indicate support of RTP/RTCP multiplexing.

[RFC5761] specifies that, if the peer endpoint does not support RTP/RTCP multiplexing, there must be a fallback to usage of different ports for RTP and RTCP. However, the RTCWEB WG have defined that the support of using different ports is optional. Therefor, there needs to be a mechanism for an endpoint to indicate exclusive support of RTP/RTCP multiplexing, i.e. indicate that the endpoint only supports RTP/RTCP multiplexing.

The document updates section 5.1.1 of [RFC5761], by defining how the SDP 'rtcp' attribute is used, together with the SDP 'rtcp-mux' attribute, to indicate exclusive support of RTP/RTCP multiplexing.

2. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. SDP Offer/Answer Considerations

When an offerer sends an offer, if the offerer supports RTP/RTCP multiplexing, the offerer must associate an SDP 'rtcp-mux' attribute

4. Update to RFC 5761

4.1. General

This section updates section 5.1.1 of [RFC5761], by replacing the text in the first paragraph with the new text defined in this section.

4.2. RFC 5761 Section 5.1.1 Update

OLD TEXT:

   When the Session Description Protocol (SDP) [8] is used to negotiate
   RTP sessions following the offer/answer model [9], the "a=rtcp-mux"
   attribute (see Section 8) indicates the desire to multiplex RTP and
   RTCP onto a single port.  The initial SDP offer MUST include this
   attribute at the media level to request multiplexing of RTP and RTCP
   on a single port.  For example:


NEW TEXT:

   When the Session Description Protocol (SDP) [8] is used to negotiate
   RTP sessions following the offer/answer model [9], the "a=rtcp-mux"
   attribute (see Section 8) indicates the desire to multiplex RTP and
   RTCP onto a single port.  The initial SDP offer MUST include this
   attribute at the media level to request multiplexing of RTP and RTCP
   on a single port. If the offerer is not able to use different ports
   for RTP and RTCP, the SDP offer MUST also include the "a=rtcp"
   attribute [10] with an attribute value identical to the associated
   port value for RTP. For example:

                        

4.3. Issues And TBDs

ISSUE #1: We may want to specify an explicit procedure for the answerer too, saying that it must select mux if it receives rtcp-mux and rtcp with the RTP port value.

ISSUE #2: We may want to specify something about the case when the answerer only supports mux, and receives an offer without mux.

5. Security Considerations

This document does not introduce new security considerations in additions to those specified in [RFC3605] and [RFC5761].

6. IANA Considerations

This document makes no requests from IANA.

7. Acknowledgments

TBD

8. Change Log

[RFC EDITOR NOTE: Please remove this section when publishing]

9. Normative References

Author's Address