tcplib: A Library of TCP Internetwork Traffic Characteristics

Peter B. Danzig, Sugih Jamin (USC), 1991

Summary

The authors observed that "present-day wide-area TCP/IP traffic cannot be accurately modeled with simply analytical expressions but instead requires a combination of detailed knowledge of the end-user apps responsible for the traffic and certain measured probability distributions as reported in [Caceres91] and [Danzig92]." Tcplib models five of the six apps that recent studies have found are responsible for 96% of Internet traffic. The paper illustrates how to incorporate tcplib into a simulator.

More detail

The five applications modeled are:

TELNET
SMTP
FTP
RLOGIN
NNTP

The library's API differentiates between interactive and bulk transfer apps. The former is limited by the user's activity; the latter by the network's MTU. Interactive apps are characterized by:

packet size
packet inter-arrival time
conversation duration

Bulk transfer apps are characterized by the total amount of bytes transferred.

In addition to the above individual app characteristics, need the arrival time of each conversation.

The library provides functions to specify each of the above characteristics. App characteristics derived from CDFs derived from from traffic traces, but (at the time of the paper) there existed no description for arrival times of data applications (phone conversations, only). Tcplib assumes an exponential interarrival time for all conversations. For each arrival time, one calls the next_app().

To test the library, the authors generated one thousand data points for each app characteristic and compared the CDF of the generated points with the CDF's of the original traces. Curves match very well.

Other

Keep in mind that tcplib was written in 1991. Internet usage has changed drastically since then so these traffic models probably wouldn't match today's usage. The most obvious omission is HTTP traffic.

Kristin Wright

Last modified: Mon Feb 28 12:23:42 MST 2000