RFC 1323 (rfc1323) - Page 2 of 37
TCP Extensions for High Performance
Alternative Format: Original Text Document
RFC 1323 TCP Extensions for High Performance May 1992
Authors' Addresses ............................................... 37
1. INTRODUCTION
The TCP protocol [Postel81] was designed to operate reliably over
almost any transmission medium regardless of transmission rate,
delay, corruption, duplication, or reordering of segments.
Production TCP implementations currently adapt to transfer rates in
the range of 100 bps to 10**7 bps and round-trip delays in the range
1 ms to 100 seconds. 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 [Jacobson88a].
The introduction of fiber optics is resulting in ever-higher
transmission speeds, and the fastest paths are moving out of the
domain for which TCP was originally engineered. This memo defines a
set of modest extensions to TCP to extend the domain of its
application to match this increasing network capability. It is based
upon and obsoletes RFC-1072 [Jacobson88b] and RFC-1185 [Jacobson90b].
There is no one-line answer to the question: "How fast can TCP go?".
There are two separate kinds of issues, performance and reliability,
and each depends upon different parameters. We discuss each in turn.
1.1 TCP Performance
TCP performance depends not upon the transfer rate itself, but
rather upon the product of the transfer rate and the round-trip
delay. This "bandwidth*delay product" measures the amount of data
that would "fill the pipe"; it is the buffer space required at
sender and receiver to obtain maximum throughput on the TCP
connection over the path, i.e., the amount of unacknowledged data
that TCP must handle in order to keep the pipeline full. TCP
performance problems arise when the bandwidth*delay product is
large. We 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 DS1-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. 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.
There are three fundamental performance problems with the current
TCP over LFN paths:
Jacobson, Braden, & Borman