RFC 3042 (rfc3042) - Page 1 of 9


Enhancing TCP's Loss Recovery Using Limited Transmit



Alternative Format: Original Text Document



Network Working Group                                          M. Allman
Request for Comments: 3042                                  NASA GRC/BBN
Category: Standards Track                                H. Balakrishnan
                                                                     MIT
                                                                S. Floyd
                                                                   ACIRI
                                                            January 2001


          Enhancing TCP's Loss Recovery Using Limited Transmit

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.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This document proposes a new Transmission Control Protocol (TCP)
   mechanism that can be used to more effectively recover lost segments
   when a connection's congestion window is small, or when a large
   number of segments are lost in a single transmission window.  The
   "Limited Transmit" algorithm calls for sending a new data segment in
   response to each of the first two duplicate acknowledgments that
   arrive at the sender.  Transmitting these segments increases the
   probability that TCP can recover from a single lost segment using the
   fast retransmit algorithm, rather than using a costly retransmission
   timeout.  Limited Transmit can be used both in conjunction with, and
   in the absence of, the TCP selective acknowledgment (SACK) mechanism.

1   Introduction

   A number of researchers have observed that TCP's loss recovery
   strategies do not work well when the congestion window at a TCP
   sender is small.  This can happen, for instance, because there is
   only a limited amount of data to send, or because of the limit
   imposed by the receiver-advertised window, or because of the
   constraints imposed by end-to-end congestion control over a
   connection with a small bandwidth-delay product
   [Riz96,Mor97,BPS+98,Bal98,LK98].  When a TCP detects a missing
   segment, it enters a loss recovery phase using one of two methods.



Allman, et al.              Standards Track