The RACK-TLP loss detection algorithm for TCP
draft-ietf-tcpm-rack-15
TCP Maintenance Working Group Y. Cheng
Internet-Draft N. Cardwell
Intended status: Standards Track N. Dukkipati
Expires: June 25, 2021 P. Jha
Google, Inc
December 22, 2020
The RACK-TLP loss detection algorithm for TCP
draft-ietf-tcpm-rack-15
Abstract
This document presents the RACK-TLP loss detection algorithm for TCP.
RACK-TLP uses per-segment transmit timestamps and selective
acknowledgements (SACK) and has two parts: RACK ("Recent
ACKnowledgment") starts fast recovery quickly using time-based
inferences derived from ACK feedback. TLP ("Tail Loss Probe")
leverages RACK and sends a probe packet to trigger ACK feedback to
avoid retransmission timeout (RTO) events. Compared to the widely
used DUPACK threshold approach, RACK-TLP detects losses more
efficiently when there are application-limited flights of data, lost
retransmissions, or data packet reordering events. It is intended to
be an alternative to the DUPACK threshold approach.
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-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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 June 25, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
Cheng, et al. Expires June 25, 2021 [Page 1]
Internet-Draft RACK December 2020
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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Background . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Motivation . . . . . . . . . . . . . . . . . . . . . . . 4
3. RACK-TLP high-level design . . . . . . . . . . . . . . . . . 5
3.1. RACK: time-based loss inferences from ACKs . . . . . . . 5
3.2. TLP: sending one segment to probe losses quickly with
RACK . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. RACK-TLP: reordering resilience with a time threshold . . 6
3.3.1. Reordering design rationale . . . . . . . . . . . . . 6
3.3.2. Reordering window adaptation . . . . . . . . . . . . 8
3.4. An Example of RACK-TLP in Action: fast recovery . . . . . 9
3.5. An Example of RACK-TLP in Action: RTO . . . . . . . . . . 10
3.6. Design Summary . . . . . . . . . . . . . . . . . . . . . 10
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 11
5. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.2. Per-segment variables . . . . . . . . . . . . . . . . . . 12
5.3. Per-connection variables . . . . . . . . . . . . . . . . 12
5.4. Per-connection timers . . . . . . . . . . . . . . . . . . 13
6. RACK Algorithm Details . . . . . . . . . . . . . . . . . . . 13
6.1. Upon transmitting a data segment . . . . . . . . . . . . 13
6.2. Upon receiving an ACK . . . . . . . . . . . . . . . . . . 14
6.3. Upon RTO expiration . . . . . . . . . . . . . . . . . . . 20
7. TLP Algorithm Details . . . . . . . . . . . . . . . . . . . . 21
7.1. Initializing state . . . . . . . . . . . . . . . . . . . 21
7.2. Scheduling a loss probe . . . . . . . . . . . . . . . . . 21
7.3. Sending a loss probe upon PTO expiration . . . . . . . . 22
7.4. Detecting losses using the ACK of the loss probe . . . . 24
7.4.1. General case: detecting packet losses using RACK . . 24
Show full document text