Internet Engineering Task Force (IETF) E. Blanton
Request for Comments: 6675 Purdue University
Obsoletes: 3517 M. Allman
Category: Standards Track ICSI
ISSN: 2070-1721 L. Wang
Juniper Networks
I. Jarvinen
M. Kojo
University of Helsinki
Y. Nishida
WIDE Project
August 2012
A Conservative Loss Recovery Algorithm Based on
Selective Acknowledgment (SACK) for TCP
Abstract
This document presents a conservative loss recovery algorithm for TCP
that is based on the use of the selective acknowledgment (SACK) TCP
option. The algorithm presented in this document conforms to the
spirit of the current congestion control specification (RFC 5681),
but allows TCP senders to recover more effectively when multiple
segments are lost from a single flight of data. This document
obsoletes RFC 3517 and describes changes from it.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 5741.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6675.
Blanton, et al. Standards Track [Page 1]RFC 6675 SACK Loss Recovery Algorithm for TCP August 2012Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
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1. Introduction
This document presents a conservative loss recovery algorithm for TCP
that is based on the use of the selective acknowledgment (SACK) TCP
option. While the TCP SACK option [RFC2018] is being steadily
deployed in the Internet [All00], there is evidence that hosts are
not using the SACK information when making retransmission and
congestion control decisions [PF01]. The goal of this document is to
outline one straightforward method for TCP implementations to use
SACK information to increase performance.
[RFC5681] allows advanced loss recovery algorithms to be used by TCP
[RFC793] provided that they follow the spirit of TCP's congestion
control algorithms [RFC5681] [RFC2914]. [RFC6582] outlines one such
advanced recovery algorithm called NewReno. This document outlines a
loss recovery algorithm that uses the SACK TCP option [RFC2018] to
enhance TCP's loss recovery. The algorithm outlined in this
document, heavily based on the algorithm detailed in [FF96], is a
conservative replacement of the fast recovery algorithm [Jac90]
[RFC5681]. The algorithm specified in this document is a
straightforward SACK-based loss recovery strategy that follows the
guidelines set in [RFC5681] and can safely be used in TCP
implementations. Alternate SACK-based loss recovery methods can be
used in TCP as implementers see fit (as long as the alternate
algorithms follow the guidelines provided in [RFC5681]). Please
note, however, that the SACK-based decisions in this document (such
as what segments are to be sent at what time) are largely decoupled
from the congestion control algorithms, and as such can be treated as
separate issues if so desired.
This document represents a revision of [RFC3517] to address several
situations that are not handled explicitly in that document. A
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