TCP ACK Rate Request Option
draft-gomez-tcpm-ack-rate-request-01
TCPM Working Group C. Gomez
Internet-Draft UPC
Intended status: Experimental J. Crowcroft
Expires: May 4, 2021 University of Cambridge
October 31, 2020
TCP ACK Rate Request Option
draft-gomez-tcpm-ack-rate-request-01
Abstract
TCP Delayed Acknowledgments (ACKs) is a widely deployed mechanism
that allows reducing protocol overhead in many scenarios. However,
Delayed ACKs may also contribute to suboptimal performance. When a
relatively large congestion window (cwnd) can be used, less frequent
ACKs may be desirable. On the other hand, in relatively small cwnd
scenarios, eliciting an immediate ACK may avoid unnecessary delays
that may be incurred by the Delayed ACKs mechanism. This document
specifies the TCP ACK Rate Request (TARR) option. This option allows
a sender to indicate the ACK rate to be used by a receiver, and it
also allows to request immediate ACKs from a receiver.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. TCP ACK Rate Request Functionality . . . . . . . . . . . . . 4
3.1. Sender behavior . . . . . . . . . . . . . . . . . . . . . 4
3.2. Receiver behavior . . . . . . . . . . . . . . . . . . . . 4
4. Option Format . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Delayed Acknowledgments (ACKs) were specified for TCP with the aim to
reduce protocol overhead [RFC1122]. With Delayed ACKs, a TCP delays
sending an ACK by up to 500 ms (often 200 ms, with lower values in
recent implementations such as ~50 ms also reported), and typically
sends an ACK for at least every second segment received in a stream
of full-sized segments. This allows combining several segments into
a single one (e.g. the application layer response to an application
layer data message, and the corresponding ACK), and also saves up to
one of every two ACKs, under many traffic patterns (e.g. bulk
transfers). The "SHOULD" requirement level for implementing Delayed
ACKs in RFC 1122, along with its expected benefits, has led to a
widespread deployment of this mechanism.
However, there exist scenarios where Delayed ACKs contribute to
suboptimal performance. We next roughly classify such scenarios into
two main categories, in terms of the congestion window (cwnd) size
and the Maximum Segment Size (MSS) that would be used therein: i)
"large" cwnd scenarios (i.e. cwnd >> MSS), and ii) "small" cwnd
scenarios (e.g. cwnd up to ~MSS).
In "large" cwnd scenarios, increasing the number of data segments
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