Browse Prior Art Database

TCP Selective Acknowledgement Options (RFC2018)

IP.com Disclosure Number: IPCOM000002571D
Original Publication Date: 1996-Oct-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 10 page(s) / 24K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

M. Mathis: AUTHOR [+4]

Abstract

TCP may experience poor performance when multiple packets are lost from one window of data. With the limited information available from cumulative acknowledgments, a TCP sender can only learn about a single lost packet per round trip time. An aggressive sender could choose to retransmit packets early, but such retransmitted segments may have already been successfully received.

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 11% of the total text.

Network Working Group M. Mathis

Request for Comments: 2018 J. Mahdavi

Category: Standards Track PSC

S. Floyd

LBNL

A. Romanow

Sun Microsystems

October 1996

TCP Selective Acknowledgment Options

Status of this Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Abstract

TCP may experience poor performance when multiple packets are lost

from one window of data. With the limited information available

from cumulative acknowledgments, a TCP sender can only learn about a

single lost packet per round trip time. An aggressive sender could

choose to retransmit packets early, but such retransmitted segments

may have already been successfully received.

A Selective Acknowledgment (SACK) mechanism, combined with a

selective repeat retransmission policy, can help to overcome these

limitations. The receiving TCP sends back SACK packets to the sender

informing the sender of data that has been received. The sender can

then retransmit only the missing data segments.

This memo proposes an implementation of SACK and discusses its

performance and related issues.

Acknowledgements

Much of the text in this document is taken directly from RFC1072 "TCP

Extensions for Long-Delay Paths" by Bob Braden and Van Jacobson. The

authors would like to thank Kevin Fall (LBNL), Christian Huitema

(INRIA), Van Jacobson (LBNL), Greg Miller (MITRE), Greg Minshall

(Ipsilon), Lixia Zhang (XEROX PARC and UCLA), Dave Borman (BSDI),

Allison Mankin (ISI) and others for their review and constructive

comments.

1. Introduction

Multiple packet losses from a window of data can have a catastrophic

effect on TCP throughput. TCP [Postel81] uses a cumulative

acknowledgment scheme in which received segments that are not at the

left edge of the receive window are not acknowledged. This forces

the sender to either wait a roundtrip time to find out about each

lost packet, or to unnecessarily retransmit segment...