Licentiate thesis 2007-004

Tools and Methods for Evaluation of Overlay Networks

Olof Rensfelt

27 September 2007

Overlay networks is a popular method to deploy new functionality which does not currently exist in the Internet. Such networks often use the peer-to-peer principle where users are both servers as well as clients at the same time. We evaluate how overlay networks performs in a mix of strong and weak peers. The overlay system of study in this thesis is Bamboo, which is based on a distributed hash table (DHT).

For the performance evaluation we use both simulations in NS-2 and emulations in the testbed PlanetLab. One of our contributions is a NS-2 implementation of the Bamboo DHT. To simulate nodes joining and leaving, NS-2 is modified to be aware of the identity of overlay nodes.

To control experiments on PlanetLab we designed Vendetta. Vendetta is both a tool to visualize network events and a tool to control the individual peer-to-peer nodes on the physical machines. PlanetLab does not support bandwidth limitations which is needed to emulate weak nodes. Therefore we designed a lightweight connectivity tool called Dtour.

Both the NS-2 and PlanetLab experiments indicate that a system like Bamboo can handle as much as 50 % weak nodes and still serve requests. Although, the lookup latency and the number of successful lookups suffer with the increased network dynamics.

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