QUIC C. Smith
Internet-Draft NVIDIA
Intended status: Informational I. Swett
Expires: 24 October 2025 Google LLC
J. Beshay
S. Jaiswal
I. Purushothaman
B. Schlinker
Meta Platforms, Inc.
22 April 2025
QUIC Extended Acknowledgement for Reporting Packet Receive Timestamps
draft-smith-quic-receive-ts-02
Abstract
This document defines an extension to the QUIC transport protocol
which supports reporting multiple packet receive timestamps for post-
handshake packets.
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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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 24 October 2025.
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Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
4. ACK Frame Wire Format . . . . . . . . . . . . . . . . . . . . 3
4.1. Timestamp Ranges . . . . . . . . . . . . . . . . . . . . 4
5. Extension Negotiation . . . . . . . . . . . . . . . . . . . . 5
5.1. Receive Timestamp Basis . . . . . . . . . . . . . . . . . 6
6. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Best-Effort Behavior . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
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.
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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.
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.
Additionally, receive timestamps can provide valuable network
telemetry, even if they are not used by the congestion controller.
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. ACK Frame Wire Format
Endpoints send ACK frames in 1-RTT packets as they otherwise would,
with 0 or more receive timestamps following the Ack Ranges and
optional ECN Counts. Receive timestamps MUST NOT be sent in Initial
or Handshake packets, because the peer would not know to use the
extended wire format. ACK frames are never sent in 0-RTT packets, so
there is no change to 0-RTT.
Once negotiated, the ACK format is identical to RFC9000, but with an
additional section for receive timestamps at the end:
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ACK Frame {
Type (i) = 0x02..0x03,
Largest Acknowledged (i),
ACK Delay (i),
ACK Range Count (i),
First ACK Range (i),
ACK Range (..) ...,
[ECN Counts (..)],
// Timestamp Extension, see {{ts-ranges}}
Receive Timestamps (..)
}
Figure 1: ACK 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].
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 4.1.
4.1. 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 Delta Largest
Acknowledged 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). Packets within a range are in descending packet number
and timestamp order. Ranges are in descending timestamp order but do
not have to be in descending packet number order.
Timestamp Ranges are structured as shown in Figure 2.
Timestamp Range {
Delta Largest Acknowledged (i),
Timestamp Delta Count (i),
Timestamp Delta (i) ...,
}
Figure 2: Timestamp Range Format
The fields that form each Timestamp Range are:
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Delta Largest Acknowledged: A variable-length integer indicating the
largest packet number in the Timestamp Range as a delta to
subtract from the Largest Acknowledged in the ACK frame. For
example, 0 indicates the range starts with the Largest
Acknowledged.
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 5.
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 5.1), 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 frame (see
Section 5):
5. Extension Negotiation
max_receive_timestamps_per_ack (0xff0a002 temporary value for
draft use): A variable-length integer indicating that the maximum
number of receive timestamps the sending endpoint would like to
receive in an ACK frame.
Each ACK frame sent MUST NOT contain more than the peer's maximum
number of receive timestamps.
receive_timestamps_exponent (0xff0a003 temporary value for draft
use): A variable-length integer indicating the exponent to be used
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when encoding and decoding timestamp delta fields in ACK frames
sent by the peer (see Section 4.1). If this value is absent, a
default value of 0 is assumed (indicating microsecond precision).
Values above 20 are invalid.
5.1. Receive Timestamp Basis
Endpoints which negotiate the extension need to determine a value,
receive_timestamp_basis, relative to which all receive timestamps for
the session will be reported (see Section 4.1).
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. The receive_timestamp_basis is a local
value that is not communicated to the peer.
Receive timestamps are reported relative to the basis, rather than in
absolute time to avoid requiring clock synchronization between
endpoints and to make the frame more compact.
6. Discussion
6.1. Best-Effort Behavior
Receive timestamps are sent on a best-effort basis. Endpoints MUST
gracefully handle scenarios where the receiver does not communicate
receive timestamps for acknowledged packets. Examples of such
scenarios are:
* A packet containing an ACK 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 5); or (b) fit the ACK frame into a packet.
7. Security Considerations
TODO Security
8. IANA Considerations
This document has no IANA actions.
9. References
9.1. Normative References
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[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., De Cicco, L., 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. and L., "pathChirp:
Efficient Available Bandwidth Estimation for Network
Paths", 2003.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Connor Smith
NVIDIA
Email: connorsmith.ietf@gmail.com
Ian Swett
Google LLC
Email: ianswett@google.com
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Joseph Beshay
Meta Platforms, Inc.
Email: jbeshay@meta.com
Sharad Jaiswal
Meta Platforms, Inc.
Email: sj77@meta.com
Ilango Purushothaman
Meta Platforms, Inc.
Email: ipurush@meta.com
Brandon Schlinker
Meta Platforms, Inc.
Email: bschlinker@meta.com
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