RACK-TLP: a time-based efficient loss detection for TCP
draft-ietf-tcpm-rack-09

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TCP Maintenance Working Group                                   Y. Cheng
Internet-Draft                                               N. Cardwell
Intended status: Standards Track                            N. Dukkipati
Expires: January 14, 2021                                         P. Jha
                                                             Google, Inc
                                                           July 13, 2020

        RACK-TLP: a time-based efficient loss detection for TCP
                        draft-ietf-tcpm-rack-09

Abstract

   This document presents the RACK-TLP loss detection algorithm for TCP.
   RACK-TLP uses per-segment transmit timestamp and selective
   acknowledgement (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 the 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

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on January 14, 2021.

Copyright Notice

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

Cheng, et al.           Expires January 14, 2021                [Page 1]
Internet-Draft                    RACK                         July 2020

   This document is subject to BCP 78 and the IETF Trust's Legal
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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 . . . . . . . . . .   9
     3.6.  Design Summary  . . . . . . . . . . . . . . . . . . . . .  10
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .  10
   5.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Per-packet 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 . . . . . . . . . . . . . . . . . .  13
     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 by 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