SDI Seminar

Speakers: Matt Mathis and Jamshid Mahdavi, CMU

Diagnosing Internet Congestion with a Transport-Layer Performance Tool

Date: June 20, 1996

Abstract: The massive growth in presented load has left many large Internet users with insufficient bandwidth to support their applications. This problem is exacerbated by the lack of performance measurements by which users can compare IP providers.

We are focusing on one particular metric, bulk transfer capacity, which requires a very clean network and has other properties that make it an important gauge of network performance. We introduce our tool, TReno, which is expected to become the basis for a formal bulk transfer metric.

Developing TReno led us to key observations about TCP behavior and influenced details of the new specifications for the TCP Selective acknowledgment (SACK) option. Currently TReno does not precisely estimate Reno performance in the Internet. As SACK is deployed, and the research community reaches consensus regarding its proper behavior, TReno and state-of-the-art TCP will converge to identical performance and behavior.

The IP Provider Metrics subcommittee of the IETF is developing standardized formal metrics for providers. There is a substantial amount of work to be completed in the areas of measurement procedures and statistics before TReno can become a standardized metric. Our goal is for the TReno development effort and the IPPM standards efforts to converge.

TReno will maximize its potential as a metric if it also functions well as a diagnostic. If a long multi-provider path between two users is not performing as well as desired, it would be extremely valuable to use TReno to measure the path hop-by-hop or provider-by-provider to localize the problem.