Linux and the Next Generation Internet

The authors describe their implementation of a demonstration environment for differentiated Internet services (Diffserv) using Linux-based routers.
Other Linux-based Diffserv Work

It would be inappropriate, particularly with respect to any open-source developments, to neglect mentioning related efforts, or efforts which have contributed to the system described in this article. Two Linux-based Diffserv projects we feel are especially interesting and mature are the efforts underway at the University of Karlsruhe (see Resources 13) and the University of Kansas (see Resources 14). Many of the conclusions and insights made available through these projects correspond with our own observations, and they are excellent sources of further information on Diffserv and differentiated services under Linux. We highly recommend them to the interested reader.

In particular, we want to call attention to the differences between the demonstration environment described in this article and the DiffSpec tool under construction at the University of Kansas. The Diffserv approach to resource allocation for each class of service very explicitly requires external intervention in the form of what has been called a “bandwidth broker” (BB). The DiffSpec tool entails a much grander system concept than the demonstration environment discussed here. For example, DiffSpec includes an API for managing queue/class/filter combinations, CORBA-based system calls for automated configuration of DS parameters, and a general web-based user interface to the Linux traffic-control capabilities.

In contrast, for the purpose of our demonstration environment, we unwittingly followed a “separation of powers” philosophy well known to students of political science. We carefully segregated the “service level definition” (or “legislative branch”) functions of the BB into a manually crafted, static database of allowable configurations. At the same time, we placed the “network instantiation” (or “executive branch”) functions of the BB onto a cleverly distributed arrangement of ipchains rules. In this fashion, we are able to reconfigure the entire network instantly to one of several predefined “looks” through either an operator's input or by an automated means. This approach may be scalable in some contexts, and it may provide for convenient “governance” of network resources, but it was not specifically intended for mass consumption.

Additionally, the structure of the Karlsruhe Diffserv implementation seems to be somewhat different than the implementation maintained by Werner Almesberger at the Swiss Federal Institute of Technology in Lausanne. For our project, we used Almesberger's distribution, so we don't have specific experience with the Karlsruhe distribution or the differences between the two implementations.


In reviewing the architecture and explicit results provided by the K.I.D.S. project (see Resources 4), we agree with their conclusions regarding strengths and weaknesses of Diffserv. In particular, through the use of our “before-after” scenario for configuring a Diffserv domain, we have experienced first-hand corroboration of these factors in the context of our “real applications”.

We also agree with Metz, who states (see Resources 1) that “In the long run it will most likely be a combination (of technologies) that will enable the Internet to offer QoS.” When the long run materializes, we're confident that Linux will be a part of the solution, because QoS in the Internet is definitely “where you want to go tomorrow”.



Michael Stricklen ( is a research assistant at the UAB Center for Telecommunications Education and Research. He enjoys tinkering with Linux projects and networking gear. When not in front of a computer, Michael would prefer to be riding a snowboard.

Bob Cummings ( is a research assistant at the UAB Center for Telecommunications Education and Research. In his spare time, he likes to spend time with friends, play RPGs and hone his Perl skills.

Stan McClellan ( is a Linux enthusiast who happens to be employed in the UAB Dept. of Electrical and Computer Engineering. When he isn't “playing Professor” by hustling research money or teaching classes, he can be found wandering around, pestering students for “interesting results”