Internet DRAFT - draft-smith-quic-receive-ts
draft-smith-quic-receive-ts
QUIC C. Smith
Internet-Draft Magic Leap, Inc.
Intended status: Informational I. Swett
Expires: 28 April 2022 Google LLC
25 October 2021
QUIC Extension for Reporting Packet Receive Timestamps
draft-smith-quic-receive-ts-00
Abstract
This document defines an extension to the QUIC transport protocol
which supports reporting multiple packet receive timestamps using a
new ACK_RECEIVE_TIMESTAMPS frame type.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the QUIC Working Group
mailing list (quic@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/quic/.
Source for this draft and an issue tracker can be found at
https://github.com/wcsmith/draft-quic-receive-ts.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 28 April 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
4. Extension Negotiation . . . . . . . . . . . . . . . . . . . . 3
4.1. Receive Timestamp Basis . . . . . . . . . . . . . . . . . 4
5. ACK_RECEIVE_TIMESTAMPS Frame . . . . . . . . . . . . . . . . 4
5.1. Timestamp Ranges . . . . . . . . . . . . . . . . . . . . 5
6. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Best-Effort Behavior . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The QUIC Transport Protocol [RFC9000] provides a secure, multiplexed
connection for transmitting reliable streams of application data.
This document defines an extension to the QUIC transport protocol
which supports reporting multiple packet receive timestamps using a
new ACK_RECEIVE_TIMESTAMPS frame type.
2. Motivation
QUIC congestion control ([RFC9002]) supports sampling round-trip time
(RTT) by measuring the time from when a packet was sent to when it is
acknowledged. However, more precise delay signals measured via
packet receive timestamps have the potential to improve the accuracy
of network bandwidth measurements and the effectiveness of congestion
control, especially for latency-critical applications such as real-
time video conferencing or game streaming.
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Numerous existing algorithms and techniques leverage receive receive
timestamps to improve transport performance. Examples include:
* The WebRTC congestion control algorithm described in
[I-D.ietf-rmcat-gcc] uses the difference between packet inter-
departure and packet inter-arrival times as the input to its
delay-based controller.
* The pathChirp ([RRBNC]) technique estimates available bandwidth by
measuring inter-arrival time of multiple packets.
Notably, these techniques require receive timestamps for more than
one packet per round-trip in order to best measure the network.
3. Conventions and Definitions
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.
4. Extension Negotiation
The use of the ACK_RECEIVE_TIMESTAMPS frame is negotiated using the
following two transport parameters (Section 7.2 of [RFC9000]):
max_receive_timestamps_per_ack (TBD): A variable-length integer
indicating that the sending endpoint would like to receive
ACK_RECEIVE_TIMESTAMPS frames from the peer containing no more
than the given maximum number of receive timestamps.
Upon receiving this parameter with a non-zero value, the peer
SHOULD send ACK_RECEIVE_TIMESTAMPS frames instead of ACK frames if
new receive timestamp information is available. The peer MAY
still send regular ACK frames (e.g. if no timing information is
available), in which case the endpoint MUST still support
processing regular ACK frames as defined by Section 19.3 of
[RFC9000].
Each ACK_RECEIVE_TIMESTAMPS frame sent MUST NOT contain more than
the specified maximum number of receive timestamps, but MAY
contain fewer or none.
receive_timestamps_exponent (TBD): A variable-length integer
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indicating the exponent to be used when encoding and decoding
timestamp delta fields in ACK_RECEIVE_TIMESTAMPS frames sent by
the peer (see Section 5.1). If this value is absent, a default
value of 0 is assumed (indicating microsecond precision). Values
above 20 are invalid.
4.1. Receive Timestamp Basis
Endpoints which send ACK_RECEIVE_TIMESTAMPS frames must determine a
value, receive_timestamp_basis, relative to which all receive
timestamps for the session will be reported (see Section 5.1).
The value of receive_timestamp_basis MUST be less than the smallest
receive timestamp reported, and MUST remain constant for the entire
duration of the session.
TODO: Discuss (here or below) why receive timestamps are reported
relative to the basis, rather than in absolute time to avoid clock
synchronization between endpoints.
5. ACK_RECEIVE_TIMESTAMPS Frame
Receivers send ACK_RECEIVE_TIMESTAMPS (type=TBD) frames in place of--
and in the same manner as--regular ACK frames as described in
Section 13.2 of [RFC9000]. However, ACK_RECEIVE_TIMESTAMPS frames
contain additional fields to report packet receive timestamps.
ACK_RECEIVE_TIMESTAMPS frames are formatted as shown in Figure 1.
ACK_RECEIVE_TIMESTAMPS Frame {
Type (i) = TBD
// Fields of the existing ACK (type=0x02) frame:
Largest Acknowledged (i),
ACK Delay (i),
ACK Range Count (i),
First ACK Range (i),
ACK Range (..) ...,
// Additional fields for ACK_RECEIVE_TIMESTAMPS:
Timestamp Range Count (i),
Timestamp Ranges (..) ...,
}
Figure 1: ACK_RECEIVE_TIMESTAMPS Frame Format
The fields Largest Acknowledged, ACK Delay, ACK Range Count, First
ACK Range, and ACK Range are the same as for ACK (type=0x02) frames
specified in Section 19.3 of [RFC9000].
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ACK_RECEIVE_TIMESTAMPS frames contain the following additional
fields:
Timestamp Range Count: A variable-length integer specifying the
number of Timestamp Range fields in the frame.
Timestamp Ranges: Ranges of receive timestamps for contiguous
packets in descending packet number order; see Section 5.1.
5.1. Timestamp Ranges
Each Timestamp Range describes a series of contiguous packet receive
timestamps in descending sequential packet number (and descending
timestamp) order. Timestamp Ranges consist of a Gap indicating the
largest packet number in the range, followed by a list of Timestamp
Deltas describing the relative receive timestamps for each contiguous
packet in the Timestamp Range (descending).
Note that reporting receive timestamps for packets received out of
order is not supported. Specifically: for any packet number P for
which a receive timestamp T is reported, all reports for packet
numbers less than P must have timestamps less than or equal to T; and
all reports for packet numbers greater than P must have timestamps
greater than or equal to T.
Timestamp Ranges are structured as shown in Figure 2.
Timestamp Range {
Gap (i),
Timestamp Delta Count (i),
Timestamp Delta (i) ...,
}
Figure 2: Timestamp Range Format
The fields that form each Timestamp Range are:
Gap: A variable-length integer indicating the largest packet number
in the Timestamp Range as follows:
For the first Timestamp Range: Gap is the difference between (a)
the Largest Acknowledged packet number in the frame and (b) the
largest packet in the current (first) Timestamp Range.
For subsequent Timestamp Ranges: Gap is the difference between (a)
the packet number two lower than the smallest packet number in the
previous Timestamp Range and (b) the largest packet in the current
Timestamp Range.
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Timestamp Delta Count: A variable-length integer indicating the
number of Timestamp Deltas in the current Timestamp Range.
The sum of Timestamp Delta Counts for all Timestamp Ranges in the
frame MUST NOT exceed max_receive_timestamps_per_ack as specified
in Section 4.
Timestamp Deltas: Variable-length integers encoding the receive
timestamp for contiguous packets in the Timestamp Range in
descending packet number order as follows:
For the first Timestamp Delta of the first Timestamp Range in the
frame: the value is the difference between (a) the receive
timestamp of the largest packet in the Timestamp Range (indicated
by Gap) and (b) the session receive_timestamp_basis (see
Section 4.1), decoded as described below.
For all other Timestamp Deltas: the value is the difference
between (a) the receive timestamp specified by the previous
Timestamp Delta and (b) the receive timestamp of the current
packet in the Timestamp Range, decoded as described below.
All Timestamp Delta values are decoded by mulitplying the value in
the field by 2 to the power of the receive_timestamps_exponent
transport parameter received by the sender of the
ACK_RECEIVE_TIMESTAMPS frame (see Section 4):
6. Discussion
6.1. Best-Effort Behavior
Receive timestamps are sent on a best-effort basis and endpoints MUST
gracefully handle scenarios where receive timestamp information for
sent packets is not received. Examples of such scenarios are:
* The packet containing the ACK_RECEIVE_TIMESTAMP frame is lost.
* The sender truncates the number of timestamps sent in order to (a)
avoid sending more than max_receive_timestamps_per_ack
(Section 4); or (b) fit the ACK frame into a packet.
7. Security Considerations
TODO Security
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8. IANA Considerations
This document has no IANA actions.
9. References
9.1. Normative References
[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/rfc/rfc2119>.
[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/rfc/rfc8174>.
[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>.
9.2. Informative References
[I-D.ietf-rmcat-gcc]
Holmer, S., Lundin, H., Carlucci, G., Cicco, L. D., and S.
Mascolo, "A Google Congestion Control Algorithm for Real-
Time Communication", Work in Progress, Internet-Draft,
draft-ietf-rmcat-gcc-02, 8 July 2016,
<https://datatracker.ietf.org/doc/html/draft-ietf-rmcat-
gcc-02>.
[RFC9002] Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", RFC 9002, DOI 10.17487/RFC9002,
May 2021, <https://www.rfc-editor.org/rfc/rfc9002>.
[RRBNC] Cottrel, R.V.R.R.B.R.N.J.a.L., "pathChirp: Efficient
Available Bandwidth Estimation for Network Paths", 2003.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Connor Smith
Magic Leap, Inc.
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Email: connorsmith.ietf@gmail.com
Ian Swett
Google LLC
Email: ianswett@google.com
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