An Unreliable Datagram Extension to QUIC
draft-pauly-quic-datagram-04

Network Working Group                                           T. Pauly
Internet-Draft                                                E. Kinnear
Intended status: Standards Track                              Apple Inc.
Expires: April 24, 2020                                      D. Schinazi
                                                              Google LLC
                                                        October 22, 2019

                An Unreliable Datagram Extension to QUIC
                      draft-pauly-quic-datagram-04

Abstract

   This document defines an extension to the QUIC transport protocol to
   add support for sending and receiving unreliable datagrams over a
   QUIC connection.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Specification of Requirements . . . . . . . . . . . . . .   2
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Transport Parameter . . . . . . . . . . . . . . . . . . . . .   3
   4.  Datagram Frame Type . . . . . . . . . . . . . . . . . . . . .   4
   5.  Behavior and Usage  . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Acknowledgement Handling  . . . . . . . . . . . . . . . .   5
     5.2.  Flow Control  . . . . . . . . . . . . . . . . . . . . . .   5
     5.3.  Congestion Control  . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The QUIC Transport Protocol [I-D.ietf-quic-transport] provides a
   secure, multiplexed connection for transmitting reliable streams of
   application data.  Reliability within QUIC is performed on a per-
   stream basis, so some frame types are not eligible for
   retransmission.

   Some applications, particularly those that need to transmit real-time
   data, prefer to transmit data unreliably.  These applications can
   build directly upon UDP [RFC0768] as a transport, and can add
   security with DTLS [RFC6347].  Extending QUIC to support transmitting
   unreliable application data would provide another option for secure
   datagrams, with the added benefit of sharing a cryptographic and
   authentication context used for reliable streams.

   This document defines four new DATAGRAM QUIC frame types, which carry
   application data without requiring retransmissions.

1.1.  Specification of Requirements

   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 BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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2.  Motivation

   Transmitting unreliable data over QUIC provides benefits over
   existing solutions:

   o  Applications that open both a reliable TLS stream and an
      unreliable DTLS flow to the same peer can benefit by sharing a
      single handshake and authentication context between a reliable
      QUIC stream and flow of unreliable QUIC datagrams.  This can
      reduce the latency required for handshakes.

   o  QUIC uses a more nuanced loss recovery mechanism than the DTLS
      handshake, which has a basic packet loss retransmission timer.
      This may allow loss recovery to occur more quickly for QUIC data.

   o  QUIC datagrams, while unreliable, can support acknowledgements,
      allowing applications to be aware of whether a datagram was
      successfully received.

   These reductions in connection latency, and application insight into
   the delivery of datagrams, can be useful for optimizing audio/video
   streaming applications, gaming applications, and other real-time
   network applications.

   Unreliable QUIC datagrams can also be used to implement an IP packet
   tunnel over QUIC, such as for a Virtual Private Network (VPN).
   Internet-layer tunneling protocols generally require a reliable and
   authenticated handshake, followed by unreliable secure transmission
   of IP packets.  This can, for example, require a TLS connection for
   the control data, and DTLS for tunneling IP packets.  A single QUIC
   connection could support both parts with the use of unreliable
   datagrams.

3.  Transport Parameter

   Support for receiving the DATAGRAM frame types is advertised by means
   of a QUIC Transport Parameter (name=max_datagram_frame_size,
   value=0x0020).  The max_datagram_frame_size transport parameter is an
   integer value (represented as a variable-length integer) that
   represents the maximum size of a DATAGRAM frame (including the frame
   type, length, and payload) the endpoint is willing to receive, in
   bytes.  An endpoint that includes this parameter supports the
   DATAGRAM frame types and is willing to receive such frames on this
   connection.  Endpoints MUST NOT send DATAGRAM frames until they have
   sent and received the max_datagram_frame_size transport parameter.
   Endpoints MUST NOT send DATAGRAM frames of size strictly larger than
   the value of max_datagram_frame_size the endpoint has received from
   its peer.  An endpoint that receives a DATAGRAM frame when it has not

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   sent the max_datagram_frame_size transport parameter MUST terminate
   the connection with error PROTOCOL_VIOLATION.  An endpoint that
   receives a DATAGRAM frame that is strictly larger than the value it
   sent in its max_datagram_frame_size transport parameter MUST
   terminate the connection with error PROTOCOL_VIOLATION.

4.  Datagram Frame Type

   DATAGRAM frames are used to transmit application data in an
   unreliable manner.  The DATAGRAM frame type takes the form 0b0011000X
   (or the values 0x30 and 0x31).  The least significant bit of the
   DATAGRAM frame type is the LEN bit (0x01).  It indicates that there
   is a Length field present.  If this bit is set to 0, the Length field
   is absent and the Datagram Data field extends to the end of the
   packet.  If this bit is set to 1, the Length field is present.

   The DATAGRAM frame is structured as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        [Length (i)]                         ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Datagram Data (*)                      ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 1: DATAGRAM Frame Format

   DATAGRAM frames contain the following fields:

   Length:  A variable-length integer specifying the length of the
      datagram in bytes.  This field is present only when the LEN bit is
      set.  If the LEN bit is not set, the datagram data extends to the
      end of the QUIC packet.

   Datagram Data:  The bytes of the datagram to be delivered.

5.  Behavior and Usage

   When an application sends an unreliable datagram over a QUIC
   connection, QUIC will generate a new DATAGRAM frame and send it in
   the first available packet.  This frame SHOULD be sent as soon as
   possible, and MAY be coalesced with other frames.

   When a QUIC endpoint receives a valid DATAGRAM frame, it SHOULD
   deliver the data to the application immediately, as long as it is
   able to process the frame and can store the contents in memory.

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   DATAGRAM frames MUST be protected with either 0-RTT or 1-RTT keys.

   Application protocols using datagrams might need to differentiate
   categories or flows of datagrams being transmitted over a single QUIC
   connection.  Each application protocol is expected to define its own
   mechanism for adding flow identifiers or similar mechanisms to the
   datagram payloads being sent over the QUIC connection.  For example,
   the use of datagrams with HTTP/3 is defined in
   [I-D.schinazi-quic-h3-datagram].

5.1.  Acknowledgement Handling

   Although DATAGRAM frames are not retransmitted upon loss detection,
   they are ack-eliciting ([I-D.ietf-quic-recovery]).  Receivers SHOULD
   support delaying ACK frames (within the limits specified by
   max_ack_delay) in reponse to receiving packets that only contain
   DATAGRAM frames, since the timing of these acknowledgements is not
   used for loss recovery.

   If a sender detects that a packet containing a specific DATAGRAM
   frame has been lost, the implementation MAY notify the application
   that the datagram was lost.  Similarly, if a packet containing a
   DATAGRAM frame is acknowledged, the implementation MAY notify the
   application that the datagram was successfully transmitted and
   received.

5.2.  Flow Control

   DATAGRAM frames do not provide any explicit flow control signaling,
   and do not contribute to any per-flow or connection-wide data limit.

   The risk associated with not providing flow control for DATAGRAM
   frames is that a receiver may not be able to commit the necessary
   resources to process the frames.  For example, it may not be able to
   store the frame contents in memory.  However, since DATAGRAM frames
   are inherently unreliable, they MAY be dropped by the receiver if the
   receiver cannot process them.

5.3.  Congestion Control

   DATAGRAM frames are subject to a QUIC connection's congestion
   control.  Specifically, if a DATAGRAM frame is enqueued to be sent by
   the application, but sending a packet with this frame is not allowed
   by the congestion control window as specified in
   [I-D.ietf-quic-recovery], the packet cannot be sent.  The sender
   implementation MUST either drop the frame without sending it (at
   which point it MAY notify the application) or else delay sending the
   frame until the window opens.

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   Implementations can optionally support allowing the application to
   specify a sending expiration time, beyond which a congestion-
   controlled DATAGRAM frame ought to be dropped without transmission.

6.  Security Considerations

   The DATAGRAM frame shares the same security properties as the rest of
   the data transmitted within a QUIC connection.  All application data
   transmitted with the DATAGRAM frame, like the STREAM frame, MUST be
   protected either by 0-RTT or 1-RTT keys.

7.  IANA Considerations

   This document registers a new value in the QUIC Transport Parameter
   Registry:

   Value:  0x0020 (if this document is approved)

   Parameter Name:  max_datagram_frame_size

   Specification:  Indicates that the connection should enable support
      for unreliable DATAGRAM frames.  An endpoint that advertises this
      transport parameter can receive datagrams frames from the other
      endpoint, up to and including the length in bytes provided in the
      transport parameter.

   This document also registers a new value in the QUIC Frame Type
   registry:

   Value:  0x30 and 0x31 (if this document is approved)

   Frame Name:  DATAGRAM

   Specification:  Unreliable application data

8.  Acknowledgments

   Thanks to Ian Swett, who inspired this proposal.

9.  References

9.1.  Normative References

   [I-D.ietf-quic-recovery]
              Iyengar, J. and I. Swett, "QUIC Loss Detection and
              Congestion Control", draft-ietf-quic-recovery-23 (work in
              progress), September 2019.

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   [I-D.ietf-quic-transport]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-23 (work
              in progress), September 2019.

9.2.  Informative References

   [I-D.schinazi-quic-h3-datagram]
              Schinazi, D., "Using QUIC Datagrams with HTTP/3", draft-
              schinazi-quic-h3-datagram-01 (work in progress), October
              2019.

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/info/rfc768>.

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

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

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

Authors' Addresses

   Tommy Pauly
   Apple Inc.
   One Apple Park Way
   Cupertino, California 95014
   United States of America

   Email: tpauly@apple.com

   Eric Kinnear
   Apple Inc.
   One Apple Park Way
   Cupertino, California 95014
   United States of America

   Email: ekinnear@apple.com

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   David Schinazi
   Google LLC
   1600 Amphitheatre Parkway
   Mountain View, California 94043
   United States of America

   Email: dschinazi.ietf@gmail.com

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