An Unreliable Datagram Extension to QUIC
draft-ietf-quic-datagram-02
Network Working Group T. Pauly
Internet-Draft E. Kinnear
Intended status: Standards Track Apple Inc.
Expires: 20 August 2021 D. Schinazi
Google LLC
16 February 2021
An Unreliable Datagram Extension to QUIC
draft-ietf-quic-datagram-02
Abstract
This document defines an extension to the QUIC transport protocol to
add support for sending and receiving unreliable datagrams over a
QUIC connection.
Discussion of this work is encouraged to happen on the QUIC IETF
mailing list quic@ietf.org (mailto:quic@ietf.org) or on the GitHub
repository which contains the draft: https://github.com/quicwg/
datagram (https://github.com/quicwg/datagram).
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
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This Internet-Draft will expire on 20 August 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Specification of Requirements . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Transport Parameter . . . . . . . . . . . . . . . . . . . . . 4
4. Datagram Frame Type . . . . . . . . . . . . . . . . . . . . . 5
5. Behavior and Usage . . . . . . . . . . . . . . . . . . . . . 5
5.1. Acknowledgement Handling . . . . . . . . . . . . . . . . 6
5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Congestion Control . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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 two new DATAGRAM QUIC frame types, which carry
application data without requiring retransmissions.
Discussion of this work is encouraged to happen on the QUIC IETF
mailing list quic@ietf.org (mailto:quic@ietf.org) or on the GitHub
repository which contains the draft: https://github.com/quicwg/
datagram (https://github.com/quicwg/datagram).
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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.
2. Motivation
Transmitting unreliable data over QUIC provides benefits over
existing solutions:
* 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.
* 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.
* QUIC datagrams, while unreliable, can support acknowledgements,
allowing applications to be aware of whether a datagram was
successfully received.
* QUIC datagrams are subject to QUIC congestion control, allowing
applications to avoid implementing their own.
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.
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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
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 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. Endpoints that wish to use
DATAGRAM frames need to ensure they send a max_datagram_frame_size
value sufficient to allow their peer to use them. It is RECOMMENDED
to send the value 65535 in the max_datagram_frame_size transport
parameter as that indicates to the peer that this endpoint will
accept any DATAGRAM frame that fits inside a QUIC packet.
The max_datagram_frame_size transport parameter is a unidirectional
limit and indication of support of DATAGRAM frames. Application
protocols that use DATAGRAM frames MAY choose to only negotiate and
use them in a single direction.
When clients use 0-RTT, they MAY store the value of the server's
max_datagram_frame_size transport parameter. Doing so allows the
client to send DATAGRAM frames in 0-RTT packets. When servers decide
to accept 0-RTT data, they MUST send a max_datagram_frame_size
transport parameter greater or equal to the value they sent to the
client in the connection where they sent them the NewSessionTicket
message. If a client stores the value of the max_datagram_frame_size
transport parameter with their 0-RTT state, they MUST validate that
the new value of the max_datagram_frame_size transport parameter sent
by the server in the handshake is greater or equal to the stored
value; if not, the client MUST terminate the connection with error
PROTOCOL_VIOLATION.
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Application protocols that use datagrams MUST define how they react
to the max_datagram_frame_size transport parameter being missing. If
datagram support is integral to the application, the application
protocol can fail the handshake if the max_datagram_frame_size
transport parameter is not present.
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. Note that empty (i.e., zero-length)
datagrams are allowed.
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 are responsible for defining
the semantics of the Datagram Data field, and how it is parsed. If
the application protocol supports the coexistence of multiple
entities using datagrams inside a single QUIC connection, it may need
a mechanism to allow demultiplexing between them. For example, using
datagrams with HTTP/3 involves prepending a flow identifier to all
datagrams, see [I-D.schinazi-quic-h3-datagram].
Note that while the max_datagram_frame_size transport parameter
places a limit on the maximum size of DATAGRAM frames, that limit can
be further reduced by the max_packet_size transport parameter, and by
the Maximum Transmission Unit (MTU) of the path between endpoints.
DATAGRAM frames cannot be fragmented, therefore application protocols
need to handle cases where the maximum datagram size is limited by
other factors.
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 might have been lost, the implementation MAY notify the
application that it believes 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. Note that, due to reordering,
a DATAGRAM frame that was thought to be lost could at a later point
be received and acknowledged.
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.
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5.3. Congestion Control
DATAGRAM frames employ the QUIC connection's congestion controller.
As a result, a connection may be unable to send a DATAGRAM frame
generated by the application until the congestion controller allows
it [I-D.ietf-quic-recovery]. The sender implementation MUST
either delay sending the frame until the controller allows it or drop
the frame without sending it (at which point it MAY notify the
application).
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
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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", Work in Progress, Internet-Draft,
draft-ietf-quic-recovery-34, 14 January 2021,
<http://www.ietf.org/internet-drafts/draft-ietf-quic-
recovery-34.txt>.
[I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", Work in Progress, Internet-Draft,
draft-ietf-quic-transport-34, 14 January 2021,
<http://www.ietf.org/internet-drafts/draft-ietf-quic-
transport-34.txt>.
9.2. Informative References
[I-D.schinazi-quic-h3-datagram]
Schinazi, D., "Using QUIC Datagrams with HTTP/3", Work in
Progress, Internet-Draft, draft-schinazi-quic-h3-datagram-
05, 12 October 2020, <http://www.ietf.org/internet-drafts/
draft-schinazi-quic-h3-datagram-05.txt>.
[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>.
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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
David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, California 94043,
United States of America
Email: dschinazi.ietf@gmail.com
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