RFC 2018 (rfc2018) - Page 1 of 12
TCP Selective Acknowledgement Options
Alternative Format: Original Text Document
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 RFC 1072 "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.
Mathis, et. al. Standards Track