RFC 889 (rfc889) - Page 1 of 11

Internet delay experiments

Network Working Group                                   D.L.  Mills
Request for Comments:  889                              December 1983


                          Internet Delay Experiments

This memo reports on some measurement experiments and suggests some possible
improvements to the TCP retransmission timeout calculation.  This memo is
both a status report on the measurements and advice to implementers of TCP.

1.  Introduction

     This memorandum describes two series of experiments designed to explore
the transmission characteristics of the Internet system.  One series of
experiments was designed to determine the network delays with respect to
packet length, while the other was designed to assess the effectiveness of the
TCP retransmission-timeout algorithm specified in the standards documents.
Both sets of experiments were conducted during the October - November 1983
time frame and used many hosts distributed throughout the Internet system.

     The objectives of these experiments were first to accumulate experimental
data on actual network paths that could be used as a benchmark of Internet
system performance, and second to apply these data to refine individual TCP
implementations and improve their performance.

     The experiments were done using a specially instrumented measurement host
called a Fuzzball, which consists of an LSI-11 running IP/TCP and various
application-layer protocols including TELNET, FTP and SMTP mail.  Among the
various measurement packages is the original PING (Packet InterNet Groper)
program used over the last six years for numerous tests and measurements of
the Internet system and its client nets.  This program contains facilities to
send various kinds of probe packets, including ICMP Echo messages, process the
reply and record elapsed times and other information in a data file, as well
as produce real-time snapshot histograms and traces.

     Following an experiment run, the data collected in the file were reduced
by another set of programs and plotted on a Peritek bit-map display with color
monitor.  The plots have been found invaluable in the indentification and
understanding of the causes of netword glitches and other "zoo" phenomena.
Finally, summary data were extracted and presented in this memorandum.  The
raw data files, including bit-map image files of the various plots, are
available to other experimenters upon request.

     The Fuzzballs and their local-net architecture, called DCN, have about
two-dozen clones scattered worldwide, including one (DCN1) at the Linkabit
Corporation offices in McLean, Virginia, and another at the Norwegian
Telecommunications Adminstration (NTA) near Oslo, Norway.  The DCN1 Fuzzball
is connected to the ARPANET at the Mitre IMP by means of 1822 Error Control
Units operating over a 56-Kbps line.  The NTA Fuzzball is connected to the
NTARE Gateway by an 1822 interface and then via VDH/HAP operating over a
9.6-Kbps line to SATNET at the Tanum (Sweden) SIMP.  For most experiments
described below, these details of the local connectivity can be ignored, since
only relatively small delays are involved.




Internet Delay Experiments