The Distributed Network Simulation Testbed is a research tool designed to aid users in the modeling and performance analysis of communication protocols. The testbed can be used to model communication networks consisting of mobile and/or immobile nodes communicating over broadcast and/or point-to-point channels. Its object-oriented design permits users to utilize previously developed modules and, when necessary, to derive new modules which are subsequently added to the testbed. The testbed, implemented in Sim ++, can run either sequentially on a single processor or in parallel on multiple processors. An object- oriented, graphical user interface allows users to monitor simulation progress for both demonstration and debugging and permits users to graphically construct network simulations from existing testbed components.