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AVTCORE Working Group                                           B. Aboba
INTERNET-DRAFT                                     Microsoft Corporation
Category: Informational                                      P. Thatcher
Expires: April 29, 2018                                           Google
                                                              C. Perkins
                                                   University of Glasgow
                                                         29 October 2017

                           QUIC Multiplexing


   If QUIC is to be used in a peer-to-peer manner, with NAT traversal,
   then it is necessary to be able to demultiplex QUIC and STUN flows
   running on a single UDP port.  This memo discusses options for how to
   perform such demultiplexing.  It also considers demultiplexing of
   QUIC and WebRTC traffic (both media and data) when running on a
   single UDP port.

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 April 29, 2018.

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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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Solutions  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  QUIC Header Changes  . . . . . . . . . . . . . . . . . . .  4
     2.2.  Multiplexing Shim  . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Heuristics . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.1. Informative references  . . . . . . . . . . . . . . . . . .  7
   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  9

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1.  Introduction

   QUIC [I-D.ietf-quic-transport] is a new network transport protocol.
   While it is initially intended as a replacement for TCP in order to
   better support HTTP/2 [RFC7540] it should eventually be useful as a
   general purpose transport. HTTP is an asymmetric client-server
   protocol, but other uses of QUIC might operate in a peer-to-peer
   manner and so will need effective NAT traversal using ICE [RFC5245],
   which which makes use of STUN [RFC5389] and TURN [RFC5766] to
   discover NAT bindings.  This STUN and TURN traffic needs to run on
   the same UDP port as the QUIC traffic. Accordingly, if QUIC is to be
   used in a peer-to-peer manner, then it needs to be possible to
   demultiplex QUIC, STUN, and TURN traffic running on a single UDP
   port. This memo discusses how to do this.

   In addition, there are a number of ways in which communication
   between WebRTC peers may utilize QUIC. One of these is transport of
   RTP over QUIC, described in [I-D.rtpfolks-quic-rtp-over-quic].
   Another is use of QUIC for data exchange. A Javascript API for use of
   QUIC in WebRTC data exchange has been incorporated into the ORTC API
   [ORTC], under development within the W3C ORTC Community Group.

   In a WebRTC scenario where ICE is utilized for NAT traversal, SRTP
   [RFC3711] is keyed using DTLS-SRTP [RFC5764] and QUIC is used for
   data exchange, RTP/RTCP [RFC3550], STUN, TURN, DTLS [RFC6347], ZRTP
   [RFC6189] and QUIC may all need to be multiplexed over a single ICE

   As noted in [RFC7983] Figure 3, protocol demultiplexing currently
   relies upon differentiation based on the first octet, as follows:

                       |        [0..3] -+--> forward to STUN
                       |                |
                       |      [16..19] -+--> forward to ZRTP
                       |                |
           packet -->  |      [20..63] -+--> forward to DTLS
                       |                |
                       |      [64..79] -+--> forward to TURN Channel
                       |                |
                       |    [128..191] -+--> forward to RTP/RTCP

        Figure 1: DTLS-SRTP receiver's packet demultiplexing algorithm.

   As noted by Colin Perkins and Lars Eggert in [QUIC-Issue] this
   creates a potential conflict with the current design of the QUIC
   headers described in [I-D.ietf-quic-transport], since the first octet

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   of the QUIC header is either:

    |1|   Type (7)  |  Long header packet

   which potentially produces values of the first octet in the range
   129-134, conflicting with RTP/RTCP, or

    |0|C|K| Type (5)|  Short header packet

   which produces values for the first octet in the ranges 1-3, 33-35,
   65-67 or 97-99, potentially conflicting with STUN, DTLS and TURN.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Solutions

   This section presents potential solutions to the QUIC multiplexing
   problem, including changes to the QUIC headers, addition of a
   multiplexing octet and use of heuristics.

2.1.  QUIC Header Changes

   As noted in [QUIC-Issue], one potential solution involves changes to
   the QUIC headers, such as setting the top two bits of the first octet
   of a QUIC packet to 1.  This would imply a reduction in the size of
   the type fields:

    |1|1|1|Type (5) |  Long header packet

    |1|1|0|C|K|Type3|  Short header packet

   Note: [QUIC-Spin] proposes to add a spin bit to the type octet within
   the QUIC header, in order to allow for RTT calculation.  This would
   leave 4 bits for the type field in the long header packet and 2 bits
   for the type field in the short header, which would accommodate the
   type field values allocated in [I-D.ietf-quic-transport].

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      The advantage to this approach is that it adds no additional
      overhead on-the-wire.  However it does require a reduction in the
      size of the QUIC Type fields and could potentially require
      allocation of the following initial octet code points for QUIC:
      For the Long header, 225-230 (241-246 when the spin bit is set)
      and for the Short header, 193-195 (209-11 with spin bit set),
      209-211 (225-227 with spin bit set) and 217-219 (233-235 with the
      spin bit set).  Utilizing all of these code points for QUIC would
      leave limited code points available for future allocations.

2.2.  Multiplexing Shim

   In this approach, an initial octet not allocated within [RFC7983]
   would be prepended to each QUIC packet, allowing QUIC packets to be
   differentiated from RTP, RTCP, DTLS, STUN, TURN and ZRTP based on the
   first octet alone. As an example, an octet with decimal value 192
   could be used:


      Advantages of this approach include simplicity and the consumption
      of only a single initial octet code point for demultiplexing of
      QUIC. The disadvantage is the addition of a single octet of
      overhead to every QUIC packet, which could impact performance
      where small payloads are exchanged, such as in peer-to-peer

2.3.  Heuristics

   During the QUIC WG interim in Seattle, Martin Thomson suggested the
   following heuristics for differentiation of QUIC packets from

   1. Demultiplex differently during the "QUIC handshake"
      and "steady state".
   2. During handshake, we only need to worry about the QUIC
      Long header, which simplifies the logic.
       a. Force all handshake packets to utilize the QUIC Long header.
       b. The QUIC Long header (0x1XXXXXXX) (or 0x11XXXXXX with
          the spin bit set) does not conflict with STUN (0x000000XX),
          DTLS (0x000XXXXX), or TURN Channel (0x01XXXXXX).
       c. The QUIC Long header does conflict with RTP/RTCP (0x10XXXXXX),
          but those packets typically aren't sent until the QUIC
          handshake is completed. Corner case: an application starts
          off with audio and video keyed with DTLS-SRTP without QUIC,
          then the application wishes to add QUIC data (e.g. the user

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          clicks on the "white-board" icon).
           i. Alternative: force the RTP padding bit to 1
              using a one-byte pad if there isn't already
              padding (pad == 0x01).  Then force QUIC to have
              a type < 64 (the current max is 8).
          ii. Alternative: Disallow QUIC in this case, use SCTP data
              exchange instead.
   3. During "steady state", we only need to worry about the QUIC
      Short header.
       a. QUIC doesn't need the Long header after the handshake.
       b. The QUIC Short header (0x0XXXXXXX or 0x01XXXXXX with
          the spin bit set) does not conflict with RTP/RTCP
          (0x10XXXXXX), so we only need to worry about
          conflicts with STUN/TURN/DTLS/ZRTP.
       c. Disallow simultaneous use of DTLS and QUIC
          Short header packets.
            i. Alternative: when using DTLS and QUIC at the same
               time, only use the QUIC Long header. Not optimal,
               but isn't really needed.
       d. ICE can be demultiplexed using the magic cookie
          and checksum.
            i. Alternative: STUN can only conflict with 3
               QUIC packet types: Version Negotiation,
               Client Initial, and Server Stateless Retry.
               Out of those, none should be needed during
               the steady state.
       e. We shouldn't need to demultiplex QUIC with TURN channel
          data or other STUN traffic. What about consent packets?

      This approach has the advantage that it requires no changes to
      QUIC headers, nor does it add any overhead to QUIC packets.
      Disadvantages include additional complexity within the
      multiplexing algorithm, the consumption of additional multiplexing
      code points, and potential future difficulties in adapting the
      algorithm to support changes to the QUIC protocol or additional
      protocols to be multiplexed.

3.  Security Considerations

   The solutions discussed in this document could potentially introduce
   some additional security considerations beyond those detailed in

   Due to the additional logic required, if mis-implemented, heuristics
   have the potential to mis-classify packets.

   When QUIC is used for only for data exchange, the TLS-within-QUIC
   exchange [I-D.ietf-quic-tls] derives keys used solely to protect the

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   QUIC data packets.  If properly implemented, this should not affect
   the transport of SRTP nor the derivation of SRTP keys via DTLS-SRTP,
   but if badly implemented, both transport and key derivation could be
   adversely impacted.

4.  IANA Considerations

   This document does not require actions by IANA.

5.  References

5.1.  Informative References

             Thomson, M. and S. Turner, "Using Transport Layer Security
             (TLS) to Secure QUIC", draft-ietf-quic-tls-07 (work in
             progress), October 13, 2017.

             Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
             and Secure Transport", draft-ietf-quic-transport-07 (work
             in progress), October 13, 2017.

             Ott, J., Even, R., Perkins, C. and V. Singh, "RTP over
             QUIC", draft-rtpfolks-quic-rtp-over-quic-01 (work in
             progress), September 1, 2017.

[ORTC]       Raymond, R., Aboba, B. and J. Uberti, "Object RTC (ORTC)
             API for WebRTC", W3C, http://draft.ortc.org/, October 2017.

[QUIC-Issue] Perkins, C., "QUIC header format/demultiplexing",
             https://github.com/quicwg/base-drafts/issues/426, March,

[QUIC-Spin]  Huitema, C., "QUIC Latency Spin Bit",
             https://github.com/quicwg/base-drafts/issues/609, June

[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-

[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, <http://www.rfc-editor.org/info/rfc3550>.

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[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,

[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-

[RFC5389]    Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
             "Session Traversal Utilities for NAT (STUN)", RFC 5389, DOI
             10.17487/RFC5389, October 2008, <http://www.rfc-

[RFC5764]    McGrew, D. and E. Rescorla, "Datagram Transport Layer
             Security (DTLS) Extension to Establish Keys for the Secure
             Real-time Transport Protocol (SRTP)", RFC 5764, DOI
             10.17487/RFC5764, May 2010, <http://www.rfc-

[RFC5766]    Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
             Relays around NAT (TURN): Relay Extensions to Session
             Traversal Utilities for NAT (STUN)", RFC 5766, DOI
             10.17487/RFC5766, April 2010, <http://www.rfc-

[RFC6189]    Zimmermann, P., Johnston, A., Ed., and J. Callas, "ZRTP:
             Media Path Key Agreement for Unicast Secure RTP", RFC 6189,
             DOI 10.17487/RFC6189, April 2011, <http://www.rfc-

[RFC6347]    Rescorla, E. and N. Modadugu, "Datagram Transport Layer
             Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
             January 2012, <http://www.rfc-editor.org/info/rfc6347>.

[RFC7540]    Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
             Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI
             10.17487/RFC7540, May 2015, <https://www.rfc-

[RFC7983]    Petit-Huguenin, M. and G. Salgueiro, "Multiplexing Scheme
             Updates for Secure Real-time Transport Protocol (SRTP)
             Extension for Datagram Transport Layer Security (DTLS)",
             RFC 7983, DOI 10.17487/RFC7983, September 2016,

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   We would like to thank Martin Thomson, Roni Even and other
   participants in the IETF QUIC and AVTCORE working groups for their
   discussion of the QUIC multiplexing issue, and their input relating
   to potential solutions.

Authors' Addresses

   Bernard Aboba
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052

   Email:  bernard.aboba@gmail.com

   Peter Thatcher
   747 6th St S
   Kirkland, WA  98033

   Email: pthatcher@google.com

   Colin Perkins
   School of Computing Science
   University of Glasgow
   Glasgow  G12 8QQ
   United Kingdom

   Email: csp@csperkins.org

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