QUIC Acknowledgement Frequency
draft-ietf-quic-ack-frequency-07
The information below is for an old version of the document.
| Document | Type |
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| Authors | Jana Iyengar , Ian Swett , Mirja Kühlewind | ||
| Last updated | 2024-02-28 (Latest revision 2023-10-27) | ||
| Replaces | draft-iyengar-quic-delayed-ack | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-quic-ack-frequency-07
QUIC J. Iyengar
Internet-Draft Fastly
Intended status: Standards Track I. Swett
Expires: 29 April 2024 Google
M. Kühlewind
Ericsson
27 October 2023
QUIC Acknowledgement Frequency
draft-ietf-quic-ack-frequency-07
Abstract
This document describes a QUIC extension for an endpoint to control
its peer's delaying of acknowledgements.
Note to Readers
Discussion of this draft takes place on the QUIC working group
mailing list (quic@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/search/?email_list=quic. Source
code and issues list for this draft can be found at
https://github.com/quicwg/ack-frequency.
Working Group information can be found at https://github.com/quicwg.
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
working documents as Internet-Drafts. The list of current Internet-
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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 29 April 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terms and Definitions . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Negotiating Extension Use . . . . . . . . . . . . . . . . . . 4
4. ACK_FREQUENCY Frame . . . . . . . . . . . . . . . . . . . . . 5
5. IMMEDIATE_ACK Frame . . . . . . . . . . . . . . . . . . . . . 6
6. Sending Acknowledgments . . . . . . . . . . . . . . . . . . . 7
6.1. Response to long idle periods . . . . . . . . . . . . . . 7
6.2. Response to Out-of-Order Packets . . . . . . . . . . . . 8
6.2.1. Examples . . . . . . . . . . . . . . . . . . . . . . 8
6.3. Setting the Reordering Threshold value . . . . . . . . . 9
6.4. Expediting Explicit Congestion Notification (ECN)
Signals . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.5. Batch Processing of Packets . . . . . . . . . . . . . . . 10
7. Computation of Probe Timeout Period . . . . . . . . . . . . . 10
8. Determining Acknowledgement Frequency . . . . . . . . . . . . 10
8.1. Congestion Control . . . . . . . . . . . . . . . . . . . 11
8.1.1. Application-Limited Connections . . . . . . . . . . . 11
8.2. Burst Mitigation . . . . . . . . . . . . . . . . . . . . 12
8.3. Loss Detection and Timers . . . . . . . . . . . . . . . . 12
8.4. Connection Migration . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10.1. QUIC Transport Parameter . . . . . . . . . . . . . . . . 14
10.2. QUIC Frame Types . . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 15
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
This document describes a QUIC extension for an endpoint to control
its peer's delaying of acknowledgements.
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1.1. Terms and Definitions
The keywords "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.
In the rest of this document, "sender" refers to a QUIC data sender
(and acknowledgement receiver). Similarly, "receiver" refers to a
QUIC data receiver (and acknowledgement sender).
An "acknowledgement packet" refers to a QUIC packet that contains
only an ACK frame.
This document uses terms, definitions, and notational conventions
described in Section 1.2 and Section 1.3 of [QUIC-TRANSPORT].
2. Motivation
A receiver acknowledges received packets, but it can delay sending
these acknowledgements. Delaying acknowledgements can impact
connection throughput, loss detection and congestion controller
performance at a data sender, and CPU utilization at both a data
sender and a data receiver.
Reducing the frequency of acknowledgements can improve connection and
endpoint performance in the following ways:
* Sending UDP packets can be very CPU intensive on some platforms.
Reducing the number of packets that only contain acknowledgements
reduces the CPU consumed at a data receiver. Experience shows
that this reduction can be critical for high bandwidth
connections.
* Similarly, receiving and processing UDP packets can also be CPU
intensive, and reducing acknowledgement frequency reduces this
cost at a data sender.
* For asymmetric link technologies, such as DOCSIS, LTE, and
satellite, connection throughput in the forward path can become
constrained when the reverse path is filled by acknowledgment
packets [RFC3449]. When traversing such links, reducing the
number of acknowledgments can achieve higher connection
throughput, lower the impact on other flows or optimise the
overall use of transmission resources [Cus22].
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* The rate of acknowledgment packets can reduce link efficiency,
including transmission opportunities or battery life, as well as
transmission opportunities available to other flows sharing the
same link.
As discussed in Section 8 however, there can be undesirable
consequences to congestion control and loss recovery if a receiver
unilitaerally reduces the acknowledgment frequency. A sender's
constraints on the acknowledgement frequency need to be taken into
account to maximize congestion controller and loss recovery
performance.
[QUIC-TRANSPORT] specifies a simple delayed acknowledgement mechanism
that a receiver can use: send an acknowledgement for every other
packet, and for every packet that is received out of order
(Section 13.2.1 of [QUIC-TRANSPORT]). This does not allow a sender
to signal its preferences or constraints. This extension provides a
mechanism to solve this problem.
3. Negotiating Extension Use
Endpoints advertise their support of the extension described in this
document by sending the following transport parameter (Section 7.2 of
[QUIC-TRANSPORT]):
min_ack_delay (0xff04de1b): A variable-length integer representing
the minimum amount of time in microseconds by which the endpoint
that is sending this value is able to delay an acknowledgement.
This limit could be based on the receiver's clock or timer
granularity. 'min_ack_delay' is used by the peer to avoid
requesting too small a value in the Request Max Ack Delay field of
the ACK_FREQUENCY frame.
An endpoint's min_ack_delay MUST NOT be greater than its
max_ack_delay. Endpoints that support this extension MUST treat
receipt of a min_ack_delay that is greater than the received
max_ack_delay as a connection error of type
TRANSPORT_PARAMETER_ERROR. Note that while the endpoint's
max_ack_delay transport parameter is in milliseconds (Section 18.2 of
[QUIC-TRANSPORT]), min_ack_delay is specified in microseconds.
The min_ack_delay transport parameter is a unilateral indication of
support for receiving ACK_FREQUENCY frames. If an endpoint sends the
transport parameter, the peer is allowed to send ACK_FREQUENCY frames
independent of whether it also sends the min_ack_delay transport
parameter or not.
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Receiving a min_ack_delay transport parameter indicates that the peer
might send ACK_FREQUENCY frames in the future. Until an
ACK_FREQUENCY frame is received, receiving this transport parameter
does not cause the endpoint to change its acknowledgement behavior.
Endpoints MUST NOT remember the value of the min_ack_delay transport
parameter they received for use in a subsequent connection.
Consequently, ACK_FREQUENCY frames cannot be sent in 0-RTT packets,
as per Section 7.4.1 of [QUIC-TRANSPORT].
This Transport Parameter is encoded as per Section 18 of
[QUIC-TRANSPORT].
4. ACK_FREQUENCY Frame
Delaying acknowledgements as much as possible reduces both work done
by the endpoints and network load. An endpoint's loss detection and
congestion control mechanisms however need to be tolerant of this
delay at the peer. An endpoint signals the frequency it wants to
receive ACK frames to its peer using an ACK_FREQUENCY frame, shown
below:
ACK_FREQUENCY Frame {
Type (i) = 0xaf,
Sequence Number (i),
Ack-Eliciting Threshold (i),
Request Max Ack Delay (i),
Reordering Threshold (i)
}
Following the common frame format described in Section 12.4 of
[QUIC-TRANSPORT], ACK_FREQUENCY frames have a type of 0xaf, and
contain the following fields:
Sequence Number: A variable-length integer representing the sequence
number assigned to the ACK_FREQUENCY frame by the sender to allow
receivers to ignore obsolete frames.
Ack-Eliciting Threshold: A variable-length integer representing the
maximum number of ack-eliciting packets the recipient of this
frame receives before sending an acknowledgment. A receiving
endpoint SHOULD send at least one ACK frame when more than this
number of ack-eliciting packets have been received. A value of 0
results in a receiver immediately acknowledging every ack-
eliciting packet. By default, an endpoint sends an ACK frame for
every other ack-eliciting packet, as specified in Section 13.2.2
of [QUIC-TRANSPORT], which corresponds to a value of 1.
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Request Max Ack Delay: A variable-length integer representing the
value to which the endpoint requests the peer update its
max_ack_delay (Section 18.2 of [QUIC-TRANSPORT]). The value of
this field is in microseconds, unlike the 'max_ack_delay'
transport parameter, which is in milliseconds. Sending a value
smaller than the min_ack_delay advertised by the peer is invalid.
Receipt of an invalid value MUST be treated as a connection error
of type TRANSPORT_PARAMETER_ERROR. On receiving a valid value in
this field, the endpoint MUST update its max_ack_delay to the
value provided by the peer.
Reordering Threshold: A variable-length integer that indicates the
maximum packet reordering before eliciting an immediate ACK, as
specified in {#out-of-order}. If no ACK_FREQUENCY frames have been
received, the endpoint immediately acknowledges any subsequent
packets that are received out-of-order, as specified in
Section 13.2 of [QUIC-TRANSPORT], corresponding to a default value
of 1. A value of 0 indicates out-of-order packets do not elicit
an immediate ACK.
ACK_FREQUENCY frames are ack-eliciting. When an ACK_FREQUENCY frame
is lost, the sender is encouraged to send another ACK_FREQUENCY
frame, unless an ACK_FREQUENCY frame with a larger Sequence Number
value has already been sent. However, it is not forbidden to
retransmit the lost frame (see Section 13.3 of [QUIC-TRANSPORT]),
because the receiver will ignore duplicate or out-of-order
ACK_FREQUENCY frames based on the Sequence Number.
An endpoint can send multiple ACK_FREQUENCY frames with different
values within a connection. A sending endpoint MUST send
monotonically increasing values in the Sequence Number field, since
this field allows ACK_FREQUENCY frames to be processed out of order.
A receiving endpoint MUST ignore a received ACK_FREQUENCY frame if
the Sequence Number value in the frame is smaller than the largest
currently processed value.
5. IMMEDIATE_ACK Frame
A sender can use an ACK_FREQUENCY frame to reduce the number of
acknowledgements sent by a receiver, but doing so increases the
likelihood that time-sensitive feedback is delayed as well. For
example, as described in Section 8.3, delaying acknowledgements can
increase the time it takes for a sender to detect packet loss.
Sending an IMMEDIATE_ACK frame can help mitigate this problem.
An IMMEDIATE_ACK frame can be useful in other situations as well.
For example, if a sender wants an immediate RTT measurement or if a
sender wants to establish receiver liveness as quickly as possible.
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PING frames (Section 19.2 of [QUIC-TRANSPORT]) are ack-eliciting, but
if a PING frame is sent without an IMMEDIATE_ACK frame, the receiver
might not immediately send an ACK based on its local ACK strategy.
By definition IMMEDIATE_ACK frames are ack-eliciting. An endpoint
SHOULD send a packet containing an ACK frame immediately upon
receiving an IMMEDIATE_ACK frame. An endpoint MAY delay sending an
ACK frame despite receiving an IMMEDIATE_ACK frame. For example, an
endpoint might do this if a large number of received packets contain
an IMMEDIATE_ACK or if the endpoint is under heavy load.
IMMEDIATE_ACK Frame {
Type (i) = 0x1f,
}
6. Sending Acknowledgments
Prior to receiving an ACK_FREQUENCY frame, endpoints send
acknowledgements as specified in Section 13.2.1 of [QUIC-TRANSPORT].
On receiving an ACK_FREQUENCY frame and updating its max_ack_delay
and Ack-Eliciting Threshold values (Section 4), the endpoint sends an
acknowledgement when one of the following conditions are met:
* Since the last acknowledgement was sent, the number of received
ack-eliciting packets is greater than the Ack-Eliciting Threshold.
* Since the last acknowledgement was sent, max_ack_delay amount of
time has passed.
Section 6.2, Section 6.4, and Section 6.5 describe exceptions to this
strategy.
6.1. Response to long idle periods
It is important to receive timely feedback after long idle periods,
e.g. update stale RTT measurements. When no acknowledgement has been
sent in over one smoothed round trip time, receivers are encouraged
to send an acknowledgement soon after receiving an ack-eliciting
packet. This is not an issue specific to this document, but the
mechanisms specified herein could create excessive delays.
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6.2. Response to Out-of-Order Packets
As specified in Section 13.2.1 of [QUIC-TRANSPORT], endpoints are
expected to send an acknowledgement immediately on receiving a
reordered ack-eliciting packet. This extension modifies that
behavior when an ACK_FREQUENCY frame with a Reordering Threshold
value other than 1 has been received.
If the most recent ACK_FREQUENCY frame received from the peer has a
Reordering Threshold value of 0, the endpoint SHOULD NOT send an
immediate acknowledgement in response to packets received out of
order, and instead rely on the peer's Ack-Eliciting Threshold and
max_ack_delay thresholds for sending acknowledgements.
If the most recent ACK_FREQUENCY frame received from the peer has a
Reordering Threshold value larger than 1, the endpoint tests the
amount of reordering before deciding to send an acknowledgement. The
specification uses the following definitions:
Largest Unacked: The largest packet number among all received ack-
eliciting packets.
Largest Acked: The Largest Acknowledged value sent in an ACK frame.
Largest Reported: The largest packet number that could be declared
lost with the specified Reordering Threshold, which is Largest
Acked - Reordering Threshold + 1.
Unreported Missing: Packets with packet numbers between the Largest
Unacked and Largest Reported that have not yet been received.
An endpoint that receives an ACK_FREQUENCY frame with a non-zero
Reordering Threshold value SHOULD send an immediate ACK when the gap
between the smallest Unreported Missing packet and the Largest
Unacked is greater than or equal to the Reordering Threshold value.
Sending this additional ACK will reset the max_ack_delay timer and
Ack-Eliciting Threshold counter (as any ACK would do).
See Section 6.2.1 for examples explaining this behavior. See
Section 6.3 for guidance on how to choose the reordering threshold
value when sending ACK_FREQUENCY frames.
6.2.1. Examples
When the reordering threshold is 1, any time a packet is received and
there is a missing packet, an immediate ACK is sent.
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If the reordering theshold is 3 and ACKs are only sent due to
reordering:
Receive 1
Receive 3 -> 2 Missing
Receive 4 -> 2 Missing
Receive 5 -> Send ACK because of 2
Receive 8 -> 6,7 Missing
Receive 9 -> Send ACK because of 6, 7 Missing
Receive 10 -> Send ACK because of 7
If the reordering threshold is 5 and ACKs are only sent due to
reordering:
Receive 1
Receive 3 -> 2 Missing
Receive 5 -> 2 Missing, 4 Missing
Receive 6 -> 2 Missing, 4 Missing
Receive 7 -> Send ACK because of 2, 4 Missing
Receive 8 -> 4 Missing
Receive 9 -> Send ACK because of 4
6.3. Setting the Reordering Threshold value
To ensure timely loss detection, it is optimal to send a Reordering
Threshold value of 1 less than the packet threshold used by the data
sender for loss detection. If the threshold is smaller, an ACK_FRAME
is sent before the packet can be declared lost based on the packet
threshold. If the value is larger, it causes unnecessary delays.
(Section 18.2 of [QUIC-RECOVERY]) recommends a default packet
threshold for loss detection of 3, equivalent to a Reordering
Threshold of 2.
6.4. Expediting Explicit Congestion Notification (ECN) Signals
An endpoint SHOULD send an immediate acknowledgement when a packet
marked with the ECN Congestion Experienced (CE) [RFC3168] codepoint
in the IP header is received and the previously received packet was
not marked CE.
Doing this maintains the peer's response time to congestion events,
while also reducing the ACK rate compared to Section 13.2.1 of
[QUIC-TRANSPORT] during extreme congestion or when peers are using
DCTCP [RFC8257] or other congestion controllers (e.g.
[I-D.ietf-tsvwg-aqm-dualq-coupled]) that mark more frequently than
classic ECN [RFC3168].
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6.5. Batch Processing of Packets
To avoid sending multiple acknowledgements in rapid succession, an
endpoint can process all packets in a batch before determining
whether to send an ACK frame in response, as stated in Section 13.2.2
of [QUIC-TRANSPORT].
7. Computation of Probe Timeout Period
On sending an update to the peer's max_ack_delay, an endpoint can use
this new value in later computations of its Probe Timeout (PTO)
period; see Section 5.2.1 of [QUIC-RECOVERY].
Until the packet carrying this frame is acknowledged, the endpoint
MUST use the greater of the current max_ack_delay and the value that
is in flight when computing the PTO period. Doing so avoids spurious
PTOs that can be caused by an update that decreases the peer's
max_ack_delay.
While it is expected that endpoints will have only one ACK_FREQUENCY
frame in flight at any given time, this extension does not prohibit
having more than one in flight. When using max_ack_delay for PTO
computations, endpoints MUST use the maximum of the current value and
all those in flight.
When the number of in-flight ack-eliciting packets is larger than the
ACK-Eliciting Threshold, an endpoint can expect that the peer will
not need to wait for its max_ack_delay period before sending an
acknowledgement. In such cases, the endpoint MAY therefore exclude
the peer's 'max_ack_delay' from its PTO calculation. When Ignore
Order is enabled and loss causes the peer to not receive enough
packets to trigger an immediate acknowledgement, the receiver will
wait 'max_ack_delay', increasing the chances of a premature PTO.
Therefore, if Ignore Order is enabled, the PTO MUST be larger than
the peer's 'max_ack_delay'.
When sending PTO packets, one can include an IMMEDIATE_ACK frame to
elicit an immediate acknowledgement. This avoids waiting the ack
delay for acknowledgements of PTO packets, reducing tail latency and
allowing the sender to exclude the peer's 'max_ack_delay' from
subsequent PTO calculations.
8. Determining Acknowledgement Frequency
This section provides some guidance on a sender's choice of
acknowledgment frequency and discusses some additional
considerations. Implementers can select an appropriate strategy to
meet the needs of their applications and congestion controllers.
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8.1. Congestion Control
A sender needs to be responsive to notifications of congestion, such
as a packet loss or an ECN CE marking. Decreasing the
acknowledgement frequency can delay a sender's response to network
congestion or cause it to underutilize the available bandwidth.
To limit the consequences of reduced acknowledgement frequency, a
sender can cause a receiver to send an acknowledgement at least once
per round trip when there are ack-eliciting packets in flight.
A sender can accomplish this by setting the Request Max Ack Delay
value to no more than the estimated round trip time. The sender can
also improve feedback and robustness to variation in the path RTT by
setting the Ack-Eliciting Threshold to a value no larger than the
current congestion window. Alternatively, a sender can accomplish
this by sending an IMMEDIATE_ACK frame once each round trip time,
although if the packet containing an IMMEDIATE_ACK is lost, detection
of that loss will be delayed by the reordering threshold or requested
max ack delay.
When setting the Request Max Ack Delay as a function of RTT, it is
usually better to use the Smoothed RTT (Section 5.3 of
[QUIC-RECOVERY]) or another estimate of the typical round trip time,
but not Min RTT. This avoids eliciting an unnecessarily high number
of acknowledgements when min_rtt is much smaller than smoothed_rtt.
Note that the congestion window and the RTT change over the lifetime
of a connection and therefore might require sending frequent
ACK_FREQUENCY frames to ensure optimal performance.
It is possible that the RTT is smaller than the receiver's timer
granularity, as communicated via the 'min_ack_delay' transport
parameter, preventing the receiver from sending an acknowledgment
every RTT in time unless packets are acknowledged immediately. In
these cases, Reordering Threshold values other than 1 can can delay
loss detection more than an RTT.
8.1.1. Application-Limited Connections
A congestion controller that is limited by the congestion window
relies upon receiving acknowledgements to send additional data into
the network. An increase in acknowledgement delay increases the
delay in sending data, which can reduce the achieved throughput.
Congestion window growth can also depend upon receiving
acknowledgements. This can be particularly significant in slow start
(Section 7.3.1 of [QUIC-RECOVERY]), when delaying acknowledgements
can delay the increase in congestion window and can create larger
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packet bursts.
If the sender is application-limited, acknowledgements can be delayed
unnecessarily when entering idle periods. Therefore, if no further
data is buffered to be sent, a sender can send an IMMEDIATE_ACK frame
with the last data packet before an idle period to avoid waiting for
the ack delay.
If there are no inflight packets, no acknowledgements will be
received for at least a round trip when sending resumes. The Max Ack
Delay and Ack-Eliciting Threshold values used by the receiver can
further delay acknowledgements. In this case, the sender can include
an IMMEDIATE_ACK or ACK_FREQUENCY frame in the first Ack-Eliciting
packet to avoid waiting for substantially more than a round trip for
an acknowledgement.
8.2. Burst Mitigation
Receiving an acknowledgement can allow a sender to release new
packets into the network. If a sender is designed to rely on the
timing of peer acknowledgments ("ACK clock"), delaying
acknowledgments can cause undesirable bursts of data into the
network. In keeping with Section 7.7 of [QUIC-RECOVERY], a sender
can either employ pacing or limit bursts to the initial congestion
window.
8.3. Loss Detection and Timers
Acknowledgements are fundamental to reliability in QUIC.
Consequently, delaying or reducing the frequency of acknowledgments
can cause loss detection at the sender to be delayed.
A QUIC sender detects loss using packet thresholds on receiving an
acknowledgement (Section 6.1.1 of [QUIC-RECOVERY]); delaying the
acknowledgement therefore delays this method of detecting losses.
Reducing acknowledgement frequency reduces the number of RTT samples
that a sender receives (Section 5 of [QUIC-RECOVERY]), making a
sender's RTT estimate less responsive to changes in the path's RTT.
As a result, any mechanisms that rely on an accurate RTT estimate,
such as time-threshold loss detection (Section 6.1.2 of
[QUIC-RECOVERY]) or Probe Timeout (Section 6.2 of [QUIC-RECOVERY]),
will be less responsive to changes in the path's RTT, resulting in
either delayed or unnecessary packet transmissions.
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A sender might use timers to detect loss of PMTU probe packets
(Section 14 of [QUIC-TRANSPORT]). A sender MAY bundle an
IMMEDIATE_ACK frame with any PMTU probes to avoid triggering such
timers.
8.4. Connection Migration
To avoid additional delays to connection migration confirmation when
using this extension, a client can bundle an IMMEDIATE_ACK frame with
the first non-probing frame (Section 9.2 of [QUIC-TRANSPORT]) it
sends or it can send only an IMMEDIATE_ACK frame, which is a non-
probing frame.
An endpoint's congestion controller and RTT estimator are reset upon
confirmation of migration (Section 9.4 of [QUIC-TRANSPORT]); this
changes the pattern of acknowledgements received after migration.
Therefore, an endpoint that has sent an ACK_FREQUENCY frame earlier
in the connection ought to send a new ACK_FREQUENCY frame upon
confirmation of connection migration with updated information, e.g.
to consider the new RTT estimate.
9. Security Considerations
An improperly configured or malicious data sender could cause a data
receiver to acknowledge more frequently than its available resources
permit. However, there are two limits that make such an attack
largely inconsequential. First, the acknowledgement rate is bounded
by the rate at which data is received. Second, ACK_FREQUENCY and
IMMEDIATE_ACK frames can only request an increase in the
acknowledgment rate, but cannot force it.
In general, with this extension, a sender cannot force a receiver to
acknowledge more frequently than the receiver considers safe based on
its resource constraints.
10. IANA Considerations
This document defines a new transport parameter to advertise support
of the extension described in this document and two new frame types
to registered by IANQ in the respective "QUIC Protocol" registries
under https://www.iana.org/assignments/quic/quic.xhtml
(https://www.iana.org/assignments/quic/quic.xhtml).
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10.1. QUIC Transport Parameter
The following entry in Table 1 has been requested to be provisionally
added to the "QUIC Transport Parameters" registry under the "QUIC
Protocol" heading.
+============+=================+===============+
| Value | Parameter Name. | Specification |
+============+=================+===============+
| 0xff04de1b | min_ack_delay | Section 3 |
+------------+-----------------+---------------+
Table 1: Addition to QUIC Transport
Parameters Entries
When this document is approved, IANA is requested to assign a
permanent allocation of a codepoint in the 0-63 range to replace the
provisional codepoint described above.
10.2. QUIC Frame Types
The following frame types have requested to be provisionally added to
the "QUIC Frame Types" registry under the "QUIC Protocol" heading.
+=======+===============+===============+
| Value | Frame Name | Specification |
+=======+===============+===============+
| 0xaf | ACK_FREQUENCY | Section 4 |
+-------+---------------+---------------+
| 0x1f | IMMEDIATE_ACK | Section 5 |
+-------+---------------+---------------+
Table 2: Addition to QUIC Frame Types
Entries
When this document is approved, IANA is requested to change the
registration to a permanent allocation of these frame types with the
values described above.
11. References
11.1. Normative References
[QUIC-TRANSPORT]
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>.
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Internet-Draft QUIC Acknowledgement Frequency October 2023
[QUIC-RECOVERY]
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>.
[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>.
11.2. Informative References
[Cus22] Custura, A., Secchi, R., and G. Fairhurst, "Reducing the
acknowledgement frequency in IETF QUIC",
DOI 10.1002/sat.1466, name IJSCN, October 2022,
<https://doi.org/10.1002/sat.1466>.
[RFC3449] Balakrishnan, H., Padmanabhan, V., Fairhurst, G., and M.
Sooriyabandara, "TCP Performance Implications of Network
Path Asymmetry", BCP 69, RFC 3449, DOI 10.17487/RFC3449,
December 2002, <https://www.rfc-editor.org/rfc/rfc3449>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/rfc/rfc3168>.
[RFC8257] Bensley, S., Thaler, D., Balasubramanian, P., Eggert, L.,
and G. Judd, "Data Center TCP (DCTCP): TCP Congestion
Control for Data Centers", RFC 8257, DOI 10.17487/RFC8257,
October 2017, <https://www.rfc-editor.org/rfc/rfc8257>.
[I-D.ietf-tsvwg-aqm-dualq-coupled]
De Schepper, K., Briscoe, B., and G. White, "Dual-Queue
Coupled Active Queue Management (AQM) for Low Latency, Low
Loss, and Scalable Throughput (L4S)", Work in Progress,
Internet-Draft, draft-ietf-tsvwg-aqm-dualq-coupled-25, 29
August 2022, <https://datatracker.ietf.org/doc/html/draft-
ietf-tsvwg-aqm-dualq-coupled-25>.
Appendix A. Change Log
*RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document.
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Acknowledgments
The following people directly contributed key ideas that shaped this
draft: Bob Briscoe, Kazuho Oku, Marten Seemann.
Authors' Addresses
Jana Iyengar
Fastly
Email: jri.ietf@gmail.com
Ian Swett
Google
Email: ianswett@google.com
Mirja Kühlewind
Ericsson
Email: mirja.kuehlewind@ericsson.com
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