An Embedded Network Simulator to

The development of network protocols, especially if designed for use in very large scale networks, generally requires extensive simulation and tests in operational environments to assess their performance and correctness. Both approaches have limitations: simulation because of possible lack of accuracy in modeling the system (and, especially, traf-c generators), tests in operating networks because of the diiculty of setting up and controlling the experimental testbed. In this paper we propose to embed network simulators in operational systems , so as to get the advantages of both simulators and real testbeds. Such simulators can be built with minimal modiications to existing protocol stacks. They work by intercepting communications of the protocol layer under test and simulating the eeects of nite queues, bandwidth limitations, communication delays, noisy channels. As a result, experiments can be run on a standalone system, while simulating arbitrarily complex networks. Thanks to the ability of using real traac generators and protocol implementations, doing experiments becomes as simple as running the desired set of applications on a workstation. An implementation of such a simulator, targeted to TCP and compatible with BSD-derived systems, is available from the author.