SDP Offer/Answer for RTP using QUIC as Transport - Design Questions
draft-dawkins-sdp-rtp-quic-questions-00
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| Author | Spencer Dawkins | ||
| Last updated | 2021-09-29 | ||
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draft-dawkins-sdp-rtp-quic-questions-00
AVTCORE/MMUSIC Working Groups S. Dawkins
Internet-Draft Tencent America LLC
Intended status: Informational 30 September 2021
Expires: 3 April 2022
SDP Offer/Answer for RTP using QUIC as Transport - Design Questions
draft-dawkins-sdp-rtp-quic-questions-00
Abstract
This document is a companion document to "SDP Offer/Answer for RTP
using QUIC as Transport". That document focuses on the description
and registration of SDP "proto" attribute parameters with IANA, to
allow applications that rely on SDP Offer/Answer to negotiate the
QUIC protocol as an encapsulation for RTP.
In writing that document, it became obvious that decisions about an
appropriate SDP description would depend on decisions about the way
RTP would be encapsulated in QUIC, and different proposals for those
encapsulations had made different assumptions. Given that none of
these proposals have been adopted by an IETF working group yet, it's
not appropriate to try to base a general-purpose set of "QUIC/RTP"
IANA registrations on any one of them, so this document includes the
questions that have come up, and (as discussions progress) suggested
answers for those questions.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the "Media Over QUIC" non-
working group mailing list (MOQ), which is archived at
https://mailarchive.ietf.org/arch/browse/moq/. Subscription
information is at https://www.ietf.org/mailman/listinfo/Moq/.
Source for this draft and an issue tracker can be found at
https://github.com/SpencerDawkins/sdp-rtp-quic-questions.
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 https://datatracker.ietf.org/drafts/current/.
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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 3 April 2022.
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
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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notes for Readers . . . . . . . . . . . . . . . . . . . . 3
1.2. Scope of this document . . . . . . . . . . . . . . . . . 3
2. Questions (and, Eventually, Answers) . . . . . . . . . . . . 4
2.1. Useful AVP Profiles . . . . . . . . . . . . . . . . . . . 4
2.1.1. Can We Assume the Use of "Extended Audiovisual
Profiles"? . . . . . . . . . . . . . . . . . . . . . 4
2.1.2. Is "Secure RTP Encapsulated in UDP" Equivalent to "RTP
Encapsulated in QUIC"? . . . . . . . . . . . . . . . 4
2.1.3. Encapsulations in Datagrams and Streams . . . . . . . 5
2.2. Useful Support For Existing RTP Extensions included in SDP
Offer/Answer . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Feedback Mechanisms . . . . . . . . . . . . . . . . . . . 5
2.4. Potential Extensions To QUIC and QUIC-related
Specifications . . . . . . . . . . . . . . . . . . . . . 6
2.4.1. QUIC Datagram Multiplexing . . . . . . . . . . . . . 6
2.4.2. RTP Destination Transport Addresses, Bundles, and QUIC
Connection-IDs . . . . . . . . . . . . . . . . . . . 7
2.4.3. Support for NAT Traversal . . . . . . . . . . . . . . 7
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Normative References . . . . . . . . . . . . . . . . . . 9
6.2. Informative References . . . . . . . . . . . . . . . . . 11
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Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
This document is a companion document to "SDP Offer/Answer for RTP
using QUIC as Transport" ([I-D.dawkins-sdp-rtp-quic]). That document
focuses on the description and registration of SDP ([RFC8866])
"proto" attribute parameters with IANA ([SDP-parameters]), to allow
applications that rely on SDP Offer/Answer ([RFC3264]) to negotiate
the QUIC protocol([RFC9000]) as an encapsulation for RTP ([RFC3550]).
In writing that document, it became obvious that decisions about an
appropriate SDP description would depend on decisions about the way
RTP would be encapsulated in QUIC, and different proposals for those
encapsulations ([I-D.engelbart-rtp-over-quic],
[I-D.hurst-quic-rtp-tunnelling], and
[I-D.rtpfolks-quic-rtp-over-quic]) had made different assumptions.
Given that none of these proposals have been adopted by an IETF
working group yet, it's not appropriate to try to base a general-
purpose set of "QUIC/RTP" IANA registrations on any one of them, so
this document includes the questions that have come up, and (as
discussions progress) suggested answers for those questions.
1.1. Notes for Readers
(Note to RFC Editor - if this document ever reaches you, please
remove this section)
This document is intended to stimulate discussion about how
proponents of "RTP over QUIC" expect that to work, recognizing that
not everyone has the same goals in mind, but it understanding what
the choices are will likely be helpful in making those choices,
especially when the results of a choice provide direction that will
allow implementers to agree on strategies and reuse as much code as
possible.
1.2. Scope of this document
[I-D.dawkins-sdp-rtp-quic] will necessarily reflect questions and
answers contained in this document, but that discussion material will
not be appropriate for inclusion in a draft that focuses on SDP
description and IANA registration. This document might be worth
publishing on its own, or some of its contents might might be
included in one or more documents that describe RTP encapsulation in
the QUIC protocol.
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2. Questions (and, Eventually, Answers)
The -00 version of this document is very much a starting point for
discussion, and this document will be updated as we converge on
answers.
2.1. Useful AVP Profiles
[SDP-parameters] contains four classes of AVP profiles:
* RTP/AVP ("RTP Profile for Audio and Video Conferences with Minimal
Control"), as defined in [RFC3551],
* RTP/SAVP ("The Secure Real-time Transport Protocol (SRTP)"), as
defined in [RFC3711],
* RTP/AVPF ("Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)"), as defined in
[RFC4585], and
* RTP/SAVPF ("Extended Secure RTP Profile for Real-time Transport
Control Protocol (RTCP)-Based Feedback (RTP/SAVPF)"), as defined
in [RFC5124].
We could register all four over QUIC, but if we can cut down on the
number of options for implementers, we might achieve better
interoperability.
2.1.1. Can We Assume the Use of "Extended Audiovisual Profiles"?
We could register both AVP and AVPF profiles, but do we need to
register both?
2.1.2. Is "Secure RTP Encapsulated in UDP" Equivalent to "RTP
Encapsulated in QUIC"?
RTP that is encapsulated in QUIC payloads will always be encrypted
[RFC9000]. So, should we register (for example)
* QUIC/RTP/AVPF, knowing that any RTP payload using the QUIC
protocol is encrypted, but is not encrypted using SDES, or
* QUIC/RTP/SAVPF, because QUIC encryption provides at least an
equivalent level of protection to SDES, or
* both QUIC/RTP/AVPF and QUIC/RTP/SAVPF, to minimize the changes
necessary for existing RTP applications to add support for QUIC
encapsulation?
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2.1.3. Encapsulations in Datagrams and Streams
We note that [SDP-parameters] contains registrations for both RTP
encapsulated in UDP datagrams and RTP encapsulated in TCP streams.
If we wanted to allow the same level of flexibility for QUIC/RTP, we
could register (for example) QUIC/DGRAM/RTP, mapped onto QUIC
datagrams ([I-D.ietf-quic-datagram]), and QUIC/STREAM/RTP, mapped
onto QUIC streams ([RFC9000]), reusing terminology from the Berkeley
Sockets API.
Should we do that? If so, starting out that way would be better than
starting out with QUIC/RTP and then adding QUIC/STREAM/RTP later.
2.2. Useful Support For Existing RTP Extensions included in SDP Offer/
Answer
At least one of the goals for QUIC/RTP encapsulation is that QUIC/RTP
applications would not require more UDP ports than existing RTP
applications.
For this reason,
* It seems useful to confirm that we can assume support for
"Multiplexing RTP Data and Control Packets on a Single Port", as
described in [RFC5761].
* It seems useful to confirm that we can assume support for Media
Multiplexing ("BUNDLE"), as described in [RFC8843].
Are there other RTP extensions that we can assume support for?
2.3. Feedback Mechanisms
RTP has relied on RTCP as its feedback mechanism for decades, as that
mechanism has evolved over time, with the addition of AVPF feedback
([RFC4585]), and subsequent extensions (for example, the codec
control messages defined in [RFC5104] and extended in [RFC7728] and
[RFC8082]).
Should we assume that RTP applications using QUIC as their transport
encapsulation will continue to use AVPF as the basis for feedback
mechanisms, largely unchanged?
Perhaps some applications will do so.
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However, [I-D.engelbart-rtp-over-quic] proposes that QUIC/RTP
implementations may not need to support some RTCP messages, if QUIC
itself provides equivalent functionality. Conversely,
[RIST-Simple-Prof] extends the RTP/AVPF bitmasked-based
retransmission request with its own range-based retransmission
request.
If there's not one answer to that question, the choice among feedback
mechanisms will need to be included in SDP Offer/Answer.
2.4. Potential Extensions To QUIC and QUIC-related Specifications
Because the topics in this section are speculative, it's not clear
whether they would have any impact on SDP description and IANA
registration in [I-D.dawkins-sdp-rtp-quic]. They are included in
this document for completeness.
2.4.1. QUIC Datagram Multiplexing
[I-D.ietf-quic-datagram] does not provide support for a standardized
datagram multiplexing identifier, for reasons described in
Section 5.1, and at greater length in the Github issue about this (at
https://github.com/quicwg/datagram/issues/6).
The high-level explanation is that there was considerable support for
adding a datagram multiplexing identifier to the datagram frame type,
but much less agreement about what effect that identifier would have,
and whether the QUIC transport layer would be responsible for any
particular processing, or whether this processing would necessarily
be performed by the application. For example, some proponents of
adding datagram multiplexing expected to use multiplexing identifiers
as ways of distinguishing between datagrams of different priorities,
and other propoents expected to used multiplexing identifiers to
distinquish between datagrams that were part of multi-datagram
conversations (more like streams, but using the datagram frame
types).
Given that there was no agreement on the functionality that datagram
multiplexer identifiers would be used for, or what requirements this
addition to the protocol would place to QUIC transport processing,
the best decision seemed to be that any application that needed this
capability could trivially add its own multiplexing identifiers at
the beginning of the Datagram Data field ([I-D.ietf-quic-datagram]).
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In general, that's a fine plan. The question for this document is
whether there is enough similarity among various applications using
QUIC/RTP that specifying an RTP-specific datagram multiplier would
provide better predictability and ability to multiplex datagrams from
different applications without modifying those applications when they
encounter each other for the first time.
2.4.2. RTP Destination Transport Addresses, Bundles, and QUIC
Connection-IDs
RTP has more than one way to identify endpoints, whether [RFC3550]-
style destination three-tuples, or [RFC4961]-style Symmetric RTP and
RTCP, or [RFC8843]-style BUNDLE transport, but all are based on IP
addresses and port addresses.
The QUIC protocol also starts out with five-tuple awareness as it
establishes a connection and performs TLS 1.3 handshake between the
client and server, as described in [RFC9001], and performs path
validation, as described in [RFC9000], but can also create multiple
connection identifiers using different transport addresses that will
be associated with the same connection, and when another path has
been validated and associated with a known connection identifier, the
QUIC endpoint can begin receiving packets for the same connection
from an entirely different transport address, with no other
signaling. This change of transport addresses might be the result of
QUIC-level "connection migration", but might also be the result of
NAT rebinding.
Applications using QUIC/RTP will need some way of managing QUIC
connection identifiers, rather than transport addresses. This points
to at least one potential need for a mapping of RTP semantics over
QUIC, equivalent to [I-D.ietf-quic-http].
If QUIC/RTP applications will be making use of something like
Application Layer Protocol Negotiation (ALPN) ([RFC7301]) identifiers
to select QUIC/RTP processing, as HTTP/3 does, this may point to
another potential need for a mapping.
2.4.3. Support for NAT Traversal
From [RFC9000], Section 8.2:
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Path validation is not designed as a NAT traversal mechanism.
Though the mechanism described here might be effective for the
creation of NAT bindings that support NAT traversal, the
expectation is that one endpoint is able to receive packets
without first having sent a packet on that path. Effective NAT
traversal needs additional synchronization mechanisms that are not
provided here.
It's worth noting that the driving use cases for the first version of
IETF QUIC have been for HTTP-based web access, where the capability
described in [RFC9000] was sufficient, while many existing
applications using RTP also require support for NAT traversal. If we
need NAT traversal for QUIC/RTP applications, we need to look at
existing NAT traversal mechanisms, and determine whether they are
sufficient, and, if not, whether they can be included in SDP Offer/
Answer for QUIC/RTP communication without modification to the
underlying QUIC path validation mechanism.
3. IANA Considerations
This document makes no requests of IANA.
4. Security Considerations
This document is intended as the basis for discussion about protocol
mechanisms that will be described in other documents. As a
discussion paper, this document introduces no new security
considerations, and any new security considerations resulting from
those discussions should be included in the documents that actually
describe protocol mechanisms.
5. Acknowledgments
Thanks to these folks, for authoring various "QUIC over RTP" drafts
for specific use cases, which included their understanding of SDP
aspects of their proposals:
* Joerg Ott, Roni Even, Colin Perkins, and Varun Singh, authors of
[I-D.rtpfolks-quic-rtp-over-quic]
* Sam Hurst, author of [I-D.hurst-quic-rtp-tunnelling]
* Joerg Ott and Mathis Engelbart, authors of
[I-D.engelbart-rtp-over-quic]
Thanks to these folks for helping to improve this draft by
commenting, proposing text, or correcting my confusion:
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* Colin Perkins
* Richard Bradbury
(Your name also could appear here. Please comment and contribute, as
described in "Contribution and Discussion Venues for this draft".).
6. References
6.1. Normative References
[I-D.engelbart-rtp-over-quic]
Ott, J. and M. Engelbart, "RTP over QUIC", Work in
Progress, Internet-Draft, draft-engelbart-rtp-over-quic-
00, 12 July 2021, <https://datatracker.ietf.org/doc/html/
draft-engelbart-rtp-over-quic-00>.
[I-D.hurst-quic-rtp-tunnelling]
Hurst, S., "QRT: QUIC RTP Tunnelling", Work in Progress,
Internet-Draft, draft-hurst-quic-rtp-tunnelling-01, 28
January 2021, <https://datatracker.ietf.org/doc/html/
draft-hurst-quic-rtp-tunnelling-01>.
[I-D.ietf-quic-datagram]
Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", Work in Progress, Internet-
Draft, draft-ietf-quic-datagram-04, 8 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
datagram-04>.
[I-D.ietf-quic-http]
Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
quic-http-34, 2 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
http-34>.
[I-D.rtpfolks-quic-rtp-over-quic]
Ott, J., Even, R., Perkins, C., and V. Singh, "RTP over
QUIC", Work in Progress, Internet-Draft, draft-rtpfolks-
quic-rtp-over-quic-01, 1 September 2017,
<https://datatracker.ietf.org/doc/html/draft-rtpfolks-
quic-rtp-over-quic-01>.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002,
<https://www.rfc-editor.org/rfc/rfc3264>.
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[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/rfc/rfc3550>.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551,
DOI 10.17487/RFC3551, July 2003,
<https://www.rfc-editor.org/rfc/rfc3551>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/rfc/rfc3711>.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
DOI 10.17487/RFC4585, July 2006,
<https://www.rfc-editor.org/rfc/rfc4585>.
[RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)",
BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007,
<https://www.rfc-editor.org/rfc/rfc4961>.
[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
"Codec Control Messages in the RTP Audio-Visual Profile
with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104,
February 2008, <https://www.rfc-editor.org/rfc/rfc5104>.
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for
Real-time Transport Control Protocol (RTCP)-Based Feedback
(RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February
2008, <https://www.rfc-editor.org/rfc/rfc5124>.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
Control Packets on a Single Port", RFC 5761,
DOI 10.17487/RFC5761, April 2010,
<https://www.rfc-editor.org/rfc/rfc5761>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
[RFC7728] Burman, B., Akram, A., Even, R., and M. Westerlund, "RTP
Stream Pause and Resume", RFC 7728, DOI 10.17487/RFC7728,
February 2016, <https://www.rfc-editor.org/rfc/rfc7728>.
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[RFC8082] Wenger, S., Lennox, J., Burman, B., and M. Westerlund,
"Using Codec Control Messages in the RTP Audio-Visual
Profile with Feedback with Layered Codecs", RFC 8082,
DOI 10.17487/RFC8082, March 2017,
<https://www.rfc-editor.org/rfc/rfc8082>.
[RFC8843] Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", RFC 8843,
DOI 10.17487/RFC8843, January 2021,
<https://www.rfc-editor.org/rfc/rfc8843>.
[RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
Session Description Protocol", RFC 8866,
DOI 10.17487/RFC8866, January 2021,
<https://www.rfc-editor.org/rfc/rfc8866>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/rfc/rfc9001>.
[RIST-Simple-Prof]
"Reliable Internet Stream Transport (RIST) Protocol
Specification – Simple Profile", September 2021,
<https://vsf.tv/download/technical_recommendations/VSF_TR-
06-1_2020_06_25.pdf>.
[SDP-parameters]
"SDP Parameters - Proto", September 2021,
<https://www.iana.org/assignments/sdp-parameters/sdp-
parameters.xhtml#sdp-parameters-2>.
6.2. Informative References
[I-D.dawkins-sdp-rtp-quic]
Dawkins, S., "SDP Offer/Answer for RTP using QUIC as
Transport", Work in Progress, Internet-Draft, draft-
dawkins-sdp-rtp-quic-00, 8 September 2021,
<https://datatracker.ietf.org/doc/html/draft-dawkins-sdp-
rtp-quic-00>.
Author's Address
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Spencer Dawkins
Tencent America LLC
United States of America
Email: spencerdawkins.ietf@gmail.com
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