Internet DRAFT - draft-ietf-mmusic-mux-exclusive
draft-ietf-mmusic-mux-exclusive
Network Working Group C. Holmberg
Internet-Draft Ericsson
Updates: 5761 (if approved) May 5, 2017
Intended status: Standards Track
Expires: November 6, 2017
Indicating Exclusive Support of RTP/RTCP Multiplexing using SDP
draft-ietf-mmusic-mux-exclusive-12.txt
Abstract
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 RFC 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 of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents 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.
Copyright Notice
Copyright (c) 2017 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SDP 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 of section 5.1.1 . . . . . . . . 7
5.3. Update to 2nd paragraph of 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. Normative References . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . 13
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) [RFC4566]
attribute, 'rtcp-mux' that can be used by entities to indicate
support, and negotiate usage of, RTP/RTCP multiplexing.
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 implement
separation of RTP and RTCP. Examples of such applications are W3C
WEBRTC [W3C.WD-webrtc-20120209] applications, that are not required
to interoperate with 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
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entities that ever need to interoperate with peers that do not
support RTC/RTCP multiplexing may harm interoperability. Also, while
the SDP answerer [RFC3264] might support, and prefer usage of,
fallback to non-multiplex, the attribute indicates that fallback to
non-multiplex cannot be enabled. One example of where non-multiplex
is preferred is where an endpoint is connected to a radio 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 endpoint may prefer
non-multiplexing also towards the other network. Otherwise the
endpoint would have to perform de-multiplexing 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], 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 document also describes the Interactive Connectivity
Establishment (ICE) [RFC5245] 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", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. SDP rtcp-mux-only Attribute
This section defines a new SDP media-level attribute, 'rtcp-mux-
only'.
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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] for the 'rtcp-
mux-only' attribute is 'IDENTICAL', which means that the attribute,
if used within a BUNDLE group
[I-D.ietf-mmusic-sdp-bundle-negotiation], 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 associated with the
attribute are defined in Section 4
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4. SDP Offer/Answer Procedures
4.1. General
This section defines the SDP offer/answer [RFC3264] procedures for
indicating exclusive support of, and negotiating usage of, RTP/RTCP
multiplexing.
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 the initial offer, if the offerer wants to
indicate exclusive RTP/RTCP multiplexing for RTP-based media, the
offerer 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, 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, associated with an RTP-based SDP media description
("m=" line), if the answerer accepts the usage of RTP/RTCP
multiplexing, the answerer 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 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.
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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, e.g., send a new offer
with a zero port value associated with the SDP media description
("m=" 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 a new offer
where the port value of the SDP media description is set to zero in
order to terminate the RTP media.
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) it is an indication
that the offerer no longer wants to use RTP/RTCP multiplexing, and
instead MUST fallback 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.
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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 that mandates it.
5. Update to RFC 5761
5.1. General
This section updates sections 5.1.1 and 5.1.3 of [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 of section 5.1.1
NOTE: [RFC8035] also updates 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 5.1.1 is moved.
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OLD 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 signalled 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.
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 of section 5.1.3
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OLD 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.
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, and the offerer MUST NOT provide a fallback port for
RTCP using the "a=rtcp:" line.
6. ICE Considerations
As defined in [RFC5245], 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 as such imply exclusive support of
RTP/RTCP multiplexing. RTCP candidates 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 mechanism using the
SDP 'rtcp-mux-only' attributes.
7. Security Considerations
This document does not introduce new security considerations in
additions to 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 of [RFC4566]. Specifically,
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it adds the SDP 'rtcp-mux-only' attribute to the table for SDP 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.
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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.
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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. 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>.
[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>.
[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>.
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[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>.
[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 in progress), December 2016.
[I-D.ietf-mmusic-sdp-bundle-negotiation]
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. 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>.
[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., Jennings, C., and A.
Narayanan, "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>.
Author's Address
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Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
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