The RACK-TLP loss detection algorithm for TCP
draft-ietf-tcpm-rack-11

Document Type Active Internet-Draft (tcpm WG)
Authors Yuchung Cheng  , Neal Cardwell  , Nandita Dukkipati  , Priyaranjan Jha 
Last updated 2020-10-07 (latest revision 2020-09-30)
Replaces draft-cheng-tcpm-rack
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Intended RFC status Proposed Standard
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Send notices to Martin Duke <martin.h.duke@gmail.com>, =?utf-8?q?Michael_T=C3=BCxen?= <tuexen@fh-muenster.de>
TCP Maintenance Working Group                                   Y. Cheng
Internet-Draft                                               N. Cardwell
Intended status: Standards Track                            N. Dukkipati
Expires: April 3, 2021                                            P. Jha
                                                             Google, Inc
                                                      September 30, 2020

             The RACK-TLP loss detection algorithm for TCP
                        draft-ietf-tcpm-rack-11

Abstract

   This document presents the RACK-TLP loss detection algorithm for TCP.
   RACK-TLP uses per-segment transmit timestamps and selective
   acknowledgements (SACK) [RFC2018] 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 in
   [RFC5681][RFC6675].

Status of This Memo

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   This Internet-Draft will expire on April 3, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Cheng, et al.             Expires April 3, 2021                 [Page 1]
Internet-Draft                    RACK                    September 2020

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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.  Per-segment variables . . . . . . . . . . . . . . . . . .  11
     5.2.  Per-connection variables  . . . . . . . . . . . . . . . .  12
   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 . . . . . . . . . . . . . . . . . . .  19
   7.  TLP Algorithm Details . . . . . . . . . . . . . . . . . . . .  20
     7.1.  Initializing state  . . . . . . . . . . . . . . . . . . .  20
     7.2.  Scheduling a loss probe . . . . . . . . . . . . . . . . .  20
     7.3.  Sending a loss probe upon PTO expiration  . . . . . . . .  21
     7.4.  Detecting losses using the ACK of the loss probe  . . . .  22
       7.4.1.  General case: detecting packet losses using RACK  . .  22
       7.4.2.  Special case: detecting a single loss repaired by the
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