RFC 3465 (rfc3465) - Page 1 of 10


TCP Congestion Control with Appropriate Byte Counting (ABC)



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Network Working Group                                          M. Allman
Request for Comments: 3465                                  BBN/NASA GRC
Category: Experimental                                     February 2003


      TCP Congestion Control with Appropriate Byte Counting (ABC)

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document proposes a small modification to the way TCP increases
   its congestion window.  Rather than the traditional method of
   increasing the congestion window by a constant amount for each
   arriving acknowledgment, the document suggests basing the increase on
   the number of previously unacknowledged bytes each ACK covers.  This
   change improves the performance of TCP, as well as closes a security
   hole TCP receivers can use to induce the sender into increasing the
   sending rate too rapidly.

Terminology

   Much of the language in this document is taken from [RFC 2581].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC 2119].

1   Introduction

   This document proposes a modification to the algorithm for increasing
   TCP's congestion window (cwnd) that improves both performance and
   security.  Rather than increasing a TCP's congestion window based on
   the number of acknowledgments (ACKs) that arrive at the data sender
   (per the current specification [RFC 2581]), the congestion window is
   increased based on the number of bytes acknowledged by the arriving
   ACKs.  The algorithm improves performance by mitigating the impact of
   delayed ACKs on the growth of cwnd.  At the same time, the algorithm
   provides cwnd growth in direct relation to the probed capacity of a



Allman                        Experimental


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