Network Working Group T. Pauly
Internet-Draft E. Kinnear
Intended status: Standards Track Apple Inc.
Expires: August 10, 2019 D. Schinazi
Google LLC
February 06, 2019
An Unreliable Datagram Extension to QUIC
draft-pauly-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.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Specification of Requirements . . . . . . . . . . . . . . 2
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Transport Parameter . . . . . . . . . . . . . . . . . . . . . 3
4. Datagram Frame Type . . . . . . . . . . . . . . . . . . . . . 4
5. Behavior and Usage . . . . . . . . . . . . . . . . . . . . . 4
5.1. Datagram Identifiers . . . . . . . . . . . . . . . . . . 5
5.2. Flow Control and Acknowledgements . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
9. Informative References . . . . . . . . . . . . . . . . . . . 6
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.
2. Motivation
Transmitting unreliable data over QUIC provides benefits over
existing solutions:
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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, datagram ID, 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 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.
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4. Datagram Frame Type
DATAGRAM frames are used to transmit application data in an
unreliable manner. The DATAGRAM frame type takes the form 0b001100XX
(or the set of values from 0x30 to 0x33). 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
second least significant bit of the DATAGRAM frame type is the
DATAGRAM_ID bit (0x02). It indicates that there is a Datagram ID
field present. If this bit is set to 0, the Datagram ID field is
absent and the Datagram ID is assumed to be zero. If this bit is set
to 1, the Datagram ID field is present.
A DATAGRAM frame is shown below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Datagram ID (i)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Length (i)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Datagram Data (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: DATAGRAM Frame Format
The fields of a DATAGRAM frame are as follows:
Datagram ID: A variable-length integer indicating the datagram ID of
the datagram (see Section 5.1).
Length: A variable-length integer specifying the length of the
datagram in bytes. If the length is zero, the 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 NOT be delayed, but
MAY be coalesced with other STREAM or DATAGRAM frames.
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When a QUIC endpoint receives a valid DATAGRAM frame, it SHOULD
deliver the data to the application immediately.
DATAGRAM frames MUST be protected with either 0-RTT or 1-RTT keys.
5.1. Datagram Identifiers
Since several applications relying on datagrams have the need to
identify which application-level flow a given datagram is a part of,
DATAGRAM frames carry a datagram identifier. Applications that do
not have a need for the identifier can use the value zero on their
DATAGRAM frames and use the DATAGRAM_ID bit to omit sending the
identifier over the wire. If an application uses a mixture of
DATAGRAM frames with and without the DATAGRAM_ID bit set, the frames
without it are assumed to be part of the application-level flow with
Datagram ID zero.
5.2. Flow Control and Acknowledgements
Although the DATAGRAM frame is not retransmitted upon loss detection,
it does contribute to the maximum data for the overall connection.
Packets that contain only DATAGRAM frames do need to be acknowledged,
but implementations SHOULD defer and batch acknowledgements since the
timing of these acknowledgements is not used for loss recovery.
The DATAGRAM frame does not provide any explicit flow control
signaling apart from the connection-level flow control. DATAGRAM
frames are flow controlled only when the maximum data for the
connection is hit, at which point the BLOCKED frame is sent.
In cases in which a DATAGRAM frame is blocked due to connection-level
flow control or congestion control, an implementation MAY drop the
frame without sending it.
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)
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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 - 0x33 (if this document is approved)
Frame Name: DATAGRAM
Specification: Unreliable application data
8. Acknowledgments
Thanks to Ian Swett, who inspired this proposal.
9. Informative References
[I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-18 (work
in progress), January 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>.
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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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