Internet DRAFT - draft-dawkins-sdp-rtp-quic-questions

draft-dawkins-sdp-rtp-quic-questions







AVTCORE/MMUSIC Working Groups                                 S. Dawkins
Internet-Draft                                       Tencent America LLC
Intended status: Informational                           25 October 2021
Expires: 28 April 2022


  SDP Offer/Answer for RTP using QUIC as Transport - Design Questions
                draft-dawkins-sdp-rtp-quic-questions-01

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
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   This Internet-Draft will expire on 28 April 2022.

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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 . . . . . . . . . . . . . . . . . . .   6
     2.4.  Potential Extensions To QUIC and QUIC-related
           Specifications  . . . . . . . . . . . . . . . . . . . . .   7
       2.4.1.  QUIC Datagram Multiplexing  . . . . . . . . . . . . .   7
       2.4.2.  RTP Destination Transport Addresses, Bundles, and QUIC
               Connection-IDs  . . . . . . . . . . . . . . . . . . .   8
       2.4.3.  Support for NAT Traversal . . . . . . . . . . . . . .   8
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  12



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   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

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 almost certainly reflect answers to
   the questions contained in this document, but the discussion material
   in this document 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, but is primarily intended to
   guide discussion that will feed into [I-D.dawkins-sdp-rtp-quic].







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2.  Questions (and, Eventually, Answers)

   This version of this document is still very much a starting point for
   discussion, and additional questions are welcomed, even 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 we could 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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2.1.2.1.  Proposed Answer

   We note that it is possible, and perhaps likely, that RTP-over-QUIC
   would be used in "mixed" environments, where one of the functions of
   an RTP mixer/translator is to connect RTP endpoints that are RTP-
   over-QUIC-enabled with RTP endpoints that are not.

   In this case, the only way to ensure encryption over every hop
   between two endpoints is to use one of the RTP profiles that includes
   security.

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].













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   *Editor's Note* We recognize that the usage of RTP/RTCP ports in (for
   example) RTP/SAVPF, which runs over UDP, will be more nuanced in (for
   example) QUIC/RTP/SAVPF, which can use UDP ports in the same way as
   RTP/SAVPF, but can also use mechanisms such as Application-Layer
   Protocol Negotiation (ALPN) Protocol IDs to multiplex multiple
   applications on a single port, as further discussed in Section 2.4.2
   below.  This section should be read with Section 2.4.2 in mind.  One
   possibility is that this discussion turns out to be about minimizing
   the need for more QUIC connections, which does translate directly to
   minimizing UDP ports.

   Are there other RTP extensions that we should 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?

   It seems likely that many implementations that already utilize
   (S)AVPF as their feedback mechanisms will continue to do so for
   QUIC/RTP/AVPF sessions.  These implementations already work, and
   continuing to use the same feedback mechanism for QUC/RTP/AVPF
   sessions will minimize the amount of new development and testing
   required for these implementations to add support for QUIC/RTP/AVPF.

   We also recognize that [RIST-Simple-Prof] extends the RTP/AVPF
   bitmasked-based retransmission request with its own range-based
   retransmission request, as an indication that this feedback mechanism
   remains in the mainstream of RTP/RTCP protocol usage.

   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.

   If there's not one answer to the feedback mechanism question, the
   necessary feedback mechanism will need to be included in the SDP
   Offer/Answer exchange.







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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 for the QUIC protocol 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]).

   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.










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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

   It's worth noting that the driving use cases for the first version of
   the IETF QUIC protocol have been for HTTP-based web access, where the
   capability described in Section 8.2 of [RFC9000] was sufficient:

      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.







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   Some existing RTP applications share this characteristic - at least
   one RTP endpoint can receive a packet without having previously sent
   packet on that path.  For these applications, current QUIC
   functionality will be sufficient.

   For other RTP applications, we may need a QUIC extension that
   provides NAT traversal, and we may need to include information about
   NAT traversal in SDP Offer/Answer to enable QUIC/RTP communication.

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 confusion:

   *  Colin Perkins

   *  Richard Bradbury

   *  Stephan Wegner

   (Your name also could appear here.  Please comment and contribute, as
   described in "Contribution and Discussion Venues for this draft"
   above)



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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-06, 5 October 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-quic-
              datagram-06>.

   [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>.

   [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>.





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   [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




Dawkins                   Expires 28 April 2022                [Page 12]

Internet-Draft          SDP O/A for RTP over QUIC           October 2021


   Spencer Dawkins
   Tencent America LLC
   United States of America

   Email: spencerdawkins.ietf@gmail.com














































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