Simulation Studies of Increased Initial TCP Window Size (RFC2415)
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2019-Feb-11
Internet Society Requests For Comment (RFCs)
K. Poduri: AUTHOR [+1]
This document covers some simulation studies of the effects of increasing the initial window size of TCP. This memo provides information for the Internet community.
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 (C) The Internet Society (1998). All Rights Reserved.
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.
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 [Page 1]
RFC 2415 TCP Window Size September 1998
2. Model and Assumptions
We simulated a network topology with a bottleneck link as shown:
10Mb, 10Mb, (all 4 links) (all 4 links)
C n2_________ ______ n6 S l n3_________\ /______ n7 e i \\ 1.5Mb, 50ms // r e n0 ------------------------ n1 v n n4__________// \ \_____ n8 e t n5__________/ \______ n9 r s s
URLs --> <--- FTP & Web data
File downloading and web-browsing clients are attached to the nodes (n2-n5) on the left-hand side. These clients are served by the FTP and Web servers attached to the nodes (n6-n9) on the right-hand side. The links to and from those nodes are at 10 Mbps. The bottleneck link is between n1 and n0. All links are bi-directional, but only ACKs, SYNs, FINs, and URLs are flowing from left to right. Some simulations were also performed with data traffic flowing from right to left simultaneously, but it had no effect on the results.
In the simulations we assumed that all ftps transferred 1-MB files a...