wdiff rfc8858.original rfc8858.txt

Network Working Group

Internet Engineering Task Force (IETF) C. Holmberg
Internet-Draft
Request for Comments: 8858 Ericsson
Updates: 5761 (if approved) May 5, 2017
Intended status: January 2021
Category: Standards Track
Expires: November 6, 2017
ISSN: 2070-1721

Indicating Exclusive Support of RTP/RTCP RTP and RTP Control Protocol (RTCP)
Multiplexing using SDP
draft-ietf-mmusic-mux-exclusive-12.txt Using the Session Description Protocol (SDP)

Abstract

This document defines a new SDP media-level Session Description Protocol (SDP) media-
level attribute, 'rtcp-mux-
only', 'rtcp-mux-only', that can be used by an endpoint to
indicate exclusive support of RTP/RTCP RTP and RTP Control Protocol (RTCP)
multiplexing. The document also updates RFC 5761, 5761 by clarifying that
an offerer can use a mechanism to indicate that it is not able to
send and receive RTCP on separate ports.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum 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 six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on November 6, 2017.
https://www.rfc-editor.org/info/rfc8858.

This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SDP rtcp-mux-only 'rtcp-mux-only' Attribute . . . . . . . . . . . . . . . . . 3
4. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 5
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Generating the Initial SDP Offer . . . . . . . . . . . . 5
4.3. Generating the Answer . . . . . . . . . . . . . . . . . . 5
4.4. Offerer Processing of the SDP Answer . . . . . . . . . . 6
4.5. Modifying the Session . . . . . . . . . . . . . . . . . . 6
5. Update to RFC 5761 . . . . . . . . . . . . . . . . . . . . . 7
5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Update to 4th paragraph Paragraph of section Section 5.1.1 . . . . . . . . 7
5.3. Update to 2nd paragraph Paragraph of section Section 5.1.3 . . . . . . . . 8
6. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1.
9.1. Normative References . . . . . . . . . . . . . . . . . . 12
11.2.
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Acknowledgements
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13

1. Introduction

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

As defined in [RFC5761], if the peer endpoint does not support RTP/
RTCP multiplexing, both endpoints should use separate ports for
sending and receiving of RTCP (referred to as fallback to usage of
separate ports for RTP and RTCP).

Some newer applications that do not require backward compatibility
with peers that cannot multiplex RTCP might choose to not to implement
separation of RTP and RTCP. Examples of such applications are W3C
WEBRTC [W3C.WD-webrtc-20120209] applications, that
WebRTC applications [WebRTC], which are not required to interoperate
with non-WEBRTC non-WebRTC clients. For such applications, this document
defines an SDP attribute to signal intent to require multiplexing.
The use of this attribute in SDP offers [RFC3264] by may harm the
interoperability of entities that ever need to interoperate with
peers that do not support RTC/RTCP multiplexing may harm interoperability. multiplexing. Also, while the SDP
answerer [RFC3264] might support, and prefer usage of, fallback to non-multiplex,
nonmultiplex, the attribute indicates that fallback to
non-multiplex nonmultiplex
cannot be enabled. One example of where non-multiplex nonmultiplex is preferred is
where an endpoint is connected to a radio interface, interface and wants to use
different bearers (possibly with different quality characteristics)
for RTP and RTCP. Another example is where the one endpoint is acting as
a gateway to a network where RTP/RTCP multiplexing cannot be used.
In such case there a case, the endpoint may prefer
non-multiplexing also prefer nonmultiplexing towards
the other network. Otherwise Otherwise, the endpoint would have to perform de-multiplexing
demultiplexing of RTP and RTCP.

This document defines a new SDP media-level attribute, 'rtcp-mux-
only', that can be used by an endpoint to indicate exclusive support
of RTP/RTCP multiplexing. The document also updates [RFC5761], [RFC5761] by
clarifying that an offerer can use a mechanism to indicate that it is
not able to send and receive RTCP on separate ports.

The

This document also describes the Interactive Connectivity
Establishment (ICE) [RFC5245] [RFC8445] considerations when indicating
exclusive support of RTP/RTCP multiplexing.

2. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in [RFC2119].
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

3. SDP rtcp-mux-only 'rtcp-mux-only' Attribute

This section defines a new SDP media-level attribute, 'rtcp-mux-
only'.

Name: rtcp-mux-only

Value: N/A

Usage Level: media

Charset Dependent: no

Syntax: rtcp-mux-only

Example: a=rtcp-mux-only

In an SDP offer, the offerer uses the SDP 'rtcp-mux-only' attribute
to indicate exclusive support of RTP/RTCP multiplexing for the RTP-
based media associated with the SDP media description ("m=" line).

In an SDP answer, the 'rtcp-mux' attribute [RFC5761] indicates that
the answerer supports, and accepts usage of, RTP/RTCP multiplexing
for the RTP-based media associated with the SDP media description
("m=" line).

The usage of the 'rtcp-mux-only' attribute in an SDP answer is
forbidden.

The usage of the SDP 'rtcp-mux-only' attribute is only defined for
RTP-based media.

The mux category [I-D.ietf-mmusic-sdp-mux-attributes] [RFC8859] for the 'rtcp-
mux-only' 'rtcp-mux-only' attribute is 'IDENTICAL',
"IDENTICAL", which means that the attribute, if used within a BUNDLE
group
[I-D.ietf-mmusic-sdp-bundle-negotiation], [RFC8843], must be associated with all multiplexed RTP-based
media descriptions within the BUNDLE group.

The 'rtcp-mux-only' attribute applies to the whole associated media
description. The attribute MUST NOT be defined per source (using the
SDP 'ssrc' attribute [RFC5576]).

The SDP offer/answer [RFC3264] procedures [RFC3264] associated with the
attribute are defined in Section 4 4.

4. SDP Offer/Answer Procedures

4.1. General

This section defines the SDP offer/answer [RFC3264] procedures [RFC3264] for
indicating exclusive support of, of RTP/RTCP multiplexing and negotiating
usage of, RTP/RTCP
multiplexing. of it.

The procedures in this section apply to individual RTP-based SDP
media descriptions ("m=" lines).

4.2. Generating the Initial SDP Offer

When an offerer sends sending the initial offer, if the offerer wants to indicate
exclusive RTP/RTCP multiplexing for RTP-based media, the
offerer it MUST
associate an SDP 'rtcp-mux-only' attribute with the associated SDP
media description ("m=" line).

In addition, if the offerer associates an SDP 'rtcp-mux-only'
attribute with an SDP media description ("m=" line, line), the offerer MUST
also associate an SDP 'rtcp-mux' attribute with the same SDP media
description ("m=" line), following the procedures in [RFC5761].

If the offerer associates an SDP 'rtcp' attribute [RFC3605] with an
SDP media description ("m=" line), and if the offerer also associates
an SDP 'rtcp-mux-only' attribute with the same SDP media description
("m=" line), the address and port values of the SDP 'rtcp' attribute
MUST match the corresponding values for RTP.

NOTE: This specification does not mandate the usage of the SDP 'rtcp'
attribute for RTP/RTCP multiplexing.

4.3. Generating the Answer

When an answerer receives an offer that contains an SDP 'rtcp-mux-
only' attribute, attribute associated with an RTP-based SDP media description
("m=" line), then if the answerer accepts the usage of RTP/RTCP
multiplexing, the answerer it MUST associate an SDP 'rtcp-mux' attribute with the
corresponding SDP media description ("m=") in the associated answer,
following the procedures in [RFC5761]. If the answerer does not
accept the usage of RTP/RTCP multiplexing, the answerer it MUST either reject the
SDP media description ("m=") by setting the port value to zero in the
associated answer, or reject the whole offer, following the
procedures in [RFC3264].

The answerer MUST NOT associate an SDP 'rtcp-mux-only' attribute with
an SDP media description ("m=" line) in the answer.

4.4. Offerer Processing of the SDP Answer

If an offerer associated an SDP 'rtcp-mux-only' attribute with an
RTP-based SDP media description ("m=" line) in an offer, and if the
corresponding SDP media description ("m=" line) in the associated
answer contains an SDP 'rtcp-mux' attribute, the offerer MUST apply
the RTP/RTCP multiplexing procedures [RFC5761] to the associated RTP-
based media. If the corresponding SDP media description ("m=" line)
in the associated answer does not contain an SDP 'rtcp-mux'
attribute, the offerer MUST either take appropriate actions in order
to disable the associated RTP-based media, media -- e.g., send a new offer
with a zero port value associated with the SDP media description
("m=" line), line) -- or send a new offer without associating an SDP 'rtcp-
mux-only' attribute with the SDP media description ("m=" line).

NOTE: This document does not mandate specific actions on how to
terminate the RTP media. The offerer might e.g. send might, for example, terminate
the RTP media by sending a new offer
where in which the port value of the
SDP media description is set to zero in
order to terminate the RTP media. zero.

4.5. Modifying the Session

When an offerer sends a subsequent offer, if the offerer and answerer
have previously negotiated usage of exclusive RTP/RTCP multiplexing
for the media associated with an RTP-based SDP media description
("m=" line), the offerer SHOULD associate an SDP 'rtcp-mux-only' with
the corresponding SDP media description ("m=" line).

In addition, if the offerer associates an SDP 'rtcp-mux-only'
attribute with an SDP media description ("m=" line), the offerer MUST
also associate an SDP 'rtcp-mux' attribute with the same SDP media
description ("m=" line), following the procedures in [RFC5761].

If the offerer does not associate the attributes with the
corresponding SDP media description ("m=" line) line), it is an indication
that the offerer no longer wants to use RTP/RTCP multiplexing, multiplexing and
instead MUST fallback fall back to usage of separate ports for RTP and RTCP
once the offer has been accepted by the answerer.

When an offerer sends a subsequent offer, if the offerer and answerer
have not previously negotiated usage of RTP/RTCP multiplexing for the
media associated with an RTP-based SDP media description ("m=" line),
the offerer MAY indicate exclusive support of RTP/RTCP multiplexing,
following the procedures in Section 4.2. The offerer MUST process
the associated answer following the procedures in Section 4.4.

It is RECOMMENDED to not switch between usage of RTP/RTCP
multiplexing and usage of separate ports for RTP and RTCP in a
subsequent offer, unless there is a use-case use case that mandates it.

5. Update to RFC 5761

5.1. General

This section updates sections Sections 5.1.1 and 5.1.3 of [RFC5761], [RFC5761] by
clarifying that an offerer can use a mechanism to indicate that it is
not able to send and receive RTCP on separate ports, and that the
offerer shall terminate the affected streams if the answerer does not
indicate support of RTP/RTCP multiplexing. It also clarifies that,
when the offerer is not able to send and receive RTCP on separate
ports, the offerer will not provide an SDP 'candidate' attribute for
RTCP, nor will the offerer provide a fallback port for RTCP (using
the SDP 'rtcp' attribute).

5.2. Update to 4th paragraph Paragraph of section Section 5.1.1

NOTE: [RFC8035] also updates section Section 5.1.1 of [RFC5761]. While the
paragraph updated in this document is not updated by [RFC8035], the
location of the paragraph within section Section 5.1.1 is moved.

OLD TEXT:

NEW TEXT:

| If the answer does not contain an "a=rtcp-mux" attribute, the
| offerer MUST NOT multiplex RTP and RTCP packets on a single port.
| Instead, it should send and receive RTCP on a port allocated
| according to the usual port-selection rules (either the port pair,
| or a signaled port if the "a=rtcp:" attribute [10] is also
| included). This will occur when talking to a peer that does not
| understand the "a=rtcp-mux" attribute. However, if the offerer
| indicated in the offer that it is not able to send and receive
| RTCP on a separate port, the offerer MUST disable the media
| streams associated with the attribute. The mechanism for
| indicating that the offerer is not able to send and receive RTCP
| on a separate port is outside the scope of this specification.

5.3. Update to 2nd paragraph Paragraph of section Section 5.1.3

OLD TEXT:

NEW TEXT:

| If it is desired to use both ICE and multiplexed RTP and RTCP, the
| initial offer MUST contain an "a=rtcp-mux" attribute to indicate
| that RTP and RTCP multiplexing is desired and MUST contain
| "a=candidate:" lines for both RTP and RTCP along with an "a=rtcp:"
| line indicating a fallback port for RTCP in the case that the
| answerer does not support RTP and RTCP multiplexing. This MUST be
| done for each media where RTP and RTCP multiplexing is desired.
| However, if the offerer indicates in the offer that it is not able
| to send and receive RTCP on a separate port, the offerer MUST NOT
| include "a=candidate:" lines for RTCP, RTCP and the offerer MUST NOT provide a
| fallback port for RTCP using the "a=rtcp:" line.

6. ICE Considerations

As defined in [RFC5245], [RFC8445], if an entity is aware that the remote peer
supports, and is willing to use, RTP/RTCP multiplexing, the entity
will only provide RTP candidates (component ID 1). However, only
providing RTP candidates does not not, as such such, imply exclusive support
of RTP/RTCP multiplexing. RTCP candidates also would not be provided also
in cases where RTCP is not supported at all. Therefore, additional
information is needed in order to indicate support of exclusive RTP/
RTCP multiplexing. This document defines such a mechanism using the
SDP 'rtcp-mux-only' attributes. attribute.

7. Security Considerations

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

8. IANA Considerations

This document updates the "Session Description Protocol Parameters"
registry as specified in Section 8.2.2 8.2.4 of [RFC4566]. Specifically,
it adds the SDP 'rtcp-mux-only' attribute to the table for SDP media media-
level attributes.

Attribute name: rtcp-mux-only

Type of attribute: media-level

Subject to charset: no

Purpose: Indicate exclusive support of RTP/RTCP multiplexing

Appropriate Values: N/A

Contact name: Christer Holmberg (christer.holmberg@ericsson.com)

Mux Category: IDENTICAL

9. Acknowledgments

Thanks to Roman Shpount, Paul Kyzivat, Ari Keranen, Bo Burman, Tomas
Frankkila and Martin Thomson for their comments and input on the
document. Thanks to Francis Dupont for the genart review.

10. Change Log

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

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-11

o Clarification note added to RFF 5761 update section.

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-10

o Changes based on comments from Ekr:

o - 'rtcp-mux-only' attribute only defined for SDP offers

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-09

o Changes based on IESG review comments from Alexey Melnikov and
Mirja Kuhlewind:

o - References to draft-mux-attributes and draft-sdp-bundle made
normative.

o - Text added regarding cases where entities might want to use non-
multiplexed RTP and RTCP.

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-08

o Editorial changes based on genart comments from Francis Dupont.

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-07

o Comments from Ben Campbell.

o - Additional text regarding applications for which the mechanism
is suitable.

o - Removal of pre-RFC5378 disclaimer.

o - Editorial fixes.

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-06

o - Editorial fix.

o - Addition of pre-RFC5378 disclaimer.

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-05

o Editorial fix.

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-04

o Changes based on comments from Flemming Andreasen.

o - Attribute mux category changed to IDENTICAL.

o - Reference to draft-5245bis changed to RFC 5245.

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-03

o Editorial changes based on comments from Martin Thomson.

o Change of attribute name.

o RFC 5761 updates added.

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-02

o Minor editorial fix.

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-01

o Mux category and source-specific applicability added.

Changes from draft-ietf-mmusic-rtcp-mux-exclusive-00

o Defined new SDP attribute for indicating rtcp-mux-exclusive.

o Updates to RFC 5761 removed.

o IANA considerations added.

Changes from draft-holmberg-mmusic-rtcp-mux-exclusive-03

o Submitted as draft-ietf-mmusic-rtcp-mux-exclusive-00.

Changes from draft-holmberg-mmusic-rtcp-mux-exclusive-02

o Intended status changed to "Standards track".

Changes from draft-holmberg-mmusic-rtcp-mux-exclusive-01

o Clarified that the SDP rtcp attribute may contain the optional IP
address part.

Changes from draft-holmberg-mmusic-rtcp-mux-exclusive-00

o Additional updates to Section 5.1.1 of RFC 5761.

o ICE considerations added.

11. References

11.1.

9.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
<https://www.rfc-editor.org/info/rfc2119>.

[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002,
<http://www.rfc-editor.org/info/rfc3264>.
<https://www.rfc-editor.org/info/rfc3264>.

[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <http://www.rfc-editor.org/info/rfc4566>.

[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>. <https://www.rfc-editor.org/info/rfc4566>.

[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
Control Packets on a Single Port", RFC 5761,
DOI 10.17487/RFC5761, April 2010,
<http://www.rfc-editor.org/info/rfc5761>.
<https://www.rfc-editor.org/info/rfc5761>.

[RFC8035] Holmberg, C., "Session Description Protocol (SDP) Offer/
Answer Clarifications for RTP/RTCP Multiplexing",
RFC 8035, DOI 10.17487/RFC8035, November 2016,
<http://www.rfc-editor.org/info/rfc8035>.

[I-D.ietf-mmusic-sdp-mux-attributes]
Nandakumar, S., "A Framework for SDP Attributes when
Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16
(work
<https://www.rfc-editor.org/info/rfc8035>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in progress), December 2016.

[I-D.ietf-mmusic-sdp-bundle-negotiation] RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018,
<https://www.rfc-editor.org/info/rfc8445>.

[RFC8843] Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
negotiation-36 (work in progress), October 2016.

11.2. RFC 8843,
DOI 10.17487/RFC8843, January 2021,
<https://www.rfc-editor.org/info/rfc8843>.

[RFC8859] Nandakumar, S., "A Framework for Session Description
Protocol (SDP) Attributes When Multiplexing", RFC 8859,
DOI 10.17487/RFC8859, January 2021,
<https://www.rfc-editor.org/info/rfc8859>.

9.2. Informative References

[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute
in Session Description Protocol (SDP)", RFC 3605,
DOI 10.17487/RFC3605, October 2003,
<http://www.rfc-editor.org/info/rfc3605>.
<https://www.rfc-editor.org/info/rfc3605>.

[RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific
Media Attributes in the Session Description Protocol
(SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009,
<http://www.rfc-editor.org/info/rfc5576>.

[W3C.WD-webrtc-20120209]
Bergkvist, A., Burnett, D.,
<https://www.rfc-editor.org/info/rfc5576>.

[WebRTC] Jennings, C., Boström, H., and A.
Narayanan, J-I. Bruaroey, "WebRTC 1.0:
Real-time Communication Between Browsers", World Wide Web Consortium WD WD-webrtc-
20120209, February 2012,
<http://www.w3.org/TR/2012/WD-webrtc-20120209>. W3C Proposed
Recommendation, <https://www.w3.org/TR/webrtc/>.

Acknowledgements

Thanks to Roman Shpount, Paul Kyzivat, Ari Keränen, Bo Burman, Tomas
Frankkila, and Martin Thomson for their comments and input on the
document. Thanks to Francis Dupont for the GENART review.

Author's Address

Christer Holmberg
Ericsson
Hirsalantie 11
FI-02420 Jorvas 02420
Finland

Email: christer.holmberg@ericsson.com