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TCP extensions for long-delay paths (RFC1072)

IP.com Disclosure Number: IPCOM000001881D
Original Publication Date: 1988-Oct-01
Included in the Prior Art Database: 2000-Sep-12
Document File: 13 page(s) / 33K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

V. Jacobson: AUTHOR [+2]

Abstract

Recent work on TCP performance has shown that TCP can work well over a variety of Internet paths, ranging from 800 Mbit/sec I/O channels to 300 bit/sec dial-up modems [Jacobson88]. However, there is still a fundamental TCP performance bottleneck for one transmission regime: paths with high bandwidth and long round-trip delays. The significant parameter is the product of bandwidth (bits per second) and round-trip delay (RTT in seconds); this product is the number of bits it takes to "fill the pipe", i.e., the amount of unacknowledged data that TCP must handle in order to keep the pipeline full. TCP performance problems arise when this product is large, e.g., significantly exceeds 10**5 bits. We will refer to an Internet path operating in this region as a "long, fat pipe", and a network containing this path as an "LFN" (pronounced "elephan(t)").

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 8% of the total text.

Network Working Group V. Jacobson

Request for Comments: 1072 LBL

R. Braden

ISI

October 1988

TCP Extensions for Long-Delay Paths

Status of This Memo

This memo proposes a set of extensions to the TCP protocol to provide

efficient operation over a path with a high bandwidth*delay product.

These extensions are not proposed as an Internet standard at this

time. Instead, they are intended as a basis for further

experimentation and research on transport protocol performance.

Distribution of this memo is unlimited.

1. INTRODUCTION

Recent work on TCP performance has shown that TCP can work well over

a variety of Internet paths, ranging from 800 Mbit/sec I/O channels

to 300 bit/sec dial-up modems [Jacobson88]. However, there is still

a fundamental TCP performance bottleneck for one transmission regime:

paths with high bandwidth and long round-trip delays. The

significant parameter is the product of bandwidth (bits per second)

and round-trip delay (RTT in seconds); this product is the number of

bits it takes to "fill the pipe", i.e., the amount of unacknowledged

data that TCP must handle in order to keep the pipeline full. TCP

performance problems arise when this product is large, e.g.,

significantly exceeds 10**5 bits. We will refer to an Internet path

operating in this region as a "long, fat pipe", and a network

containing this path as an "LFN" (pronounced "elephan(t)").

High-capacity packet satellite channels (e.g., DARPA's Wideband Net)

are LFN's. For example, a T1-speed satellite channel has a

bandwidth*delay product of 10**6 bits or more; this corresponds to

100 outstanding TCP segments of 1200 bytes each! Proposed future

terrestrial fiber-optical paths will also fall into the LFN class;

for example, a cross-country delay of 30 ms at a DS3 bandwidth

(45Mbps) also exceeds 10**6 bits.

Clever algorithms alone will not give us good TCP performance over

LFN's; it will be necessary to actually extend the protocol. This

RFC proposes a set of TCP extensions for this purpose.

There are three fundamental problems with the current TCP over LFN

paths:

(1) Window Size Limitation

The TCP header uses a 16 bit field to report the receive window

size to the sender. Therefore, the largest window that can be

used is 2**16 = 65K bytes. (In practice, some TCP

...