RFC 2415 (rfc2415) - Page 1 of 11


Simulation Studies of Increased Initial TCP Window Size



Alternative Format: Original Text Document



Network Working Group                                            K. Poduri
Request for Comments: 2415                                      K. Nichols
Category: Informational                                       Bay Networks
                                                            September 1998


        Simulation Studies of Increased Initial TCP Window Size

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   An increase in the permissible initial window size of a TCP
   connection, from one segment to three or four segments, has been
   under discussion in the tcp-impl working group. This document covers
   some simulation studies of the effects of increasing the initial
   window size of TCP. Both long-lived TCP connections (file transfers)
   and short-lived web-browsing style connections were modeled. The
   simulations were performed using the publicly available ns-2
   simulator and our custom models and files are also available.

1. Introduction

   We present results from a set of simulations with increased TCP
   initial window (IW). The main objectives were to explore the
   conditions under which the larger IW was a "win" and to determine the
   effects, if any, the larger IW might have on other traffic flows
   using an IW of one segment.

   This study was inspired by discussions at the Munich IETF tcp-impl
   and tcp-sat meetings. A proposal to increase the IW size to about 4K
   bytes (4380 bytes in the case of 1460 byte segments) was discussed.
   Concerns about both the utility of the increase and its effect on
   other traffic were raised. Some studies were presented showing the
   positive effects of increased IW on individual connections, but no
   studies were shown with a wide variety of simultaneous traffic flows.
   It appeared that some of the questions being raised could be
   addressed in an ns-2 simulation. Early results from our simulations
   were previously posted to the tcp-impl mailing list and presented at
   the tcp-impl WG meeting at the December 1997 IETF.



Poduri & Nichols             Informational