Conclusion

As the Internet grows larger and more heterogenous, it becomes more important, but more difficult, for us to understand its most fundamental aspects. The ability to measure metrics such as link bandwidth is essential, but the power of measurement models and techniques must keep pace with the size and complexity of the Internet.

In this paper we present a new deterministic model of packet delay that unifies previous models. From this model, we derive a new technique, called packet tailgating, to measure link bandwidths along a path through the Internet. Preliminary measurements from our prototype implementation show that it places an order of magnitude less load on the network than previous measurement techniques while maintaining similar accuracy. The technique can theoretically measure multi-channel links, can be run on multicast trees, does not rely on consistent behavior of routers handling ICMP packets, and does not rely on timely delivery of acknowledgments. Ultimately, the tailgating technique depends only on the existence of store-and-forward routers, the IP TTL mechanism, and packet queueing.

We are adding several features to nettimer. First, we are enhancing the implementation to measure multi-channel links. Second, we are reducing its vulnerability to noise by using one-way packet delay measurements rather than acknowledgements, and by using finer-grained timing information. Finally, we are exploring its use on a variety of different types of links, including wireless links and DSL. The source code for nettimer is available via our web site:
http://www.stanford.edu/$\sim$laik/projects/nettimer/.