Simulation-assisted analysis and design of STP-based networks

In this paper we analyze, through simulations, the performance of Spanning Tree Protocol (STP)-based Ethernet networks with ring and double ring topologies. In particular, we consider both the presence and the absence of Virtual Local Area Networks (VLANs), and we derive the optimized STP parameters which minimize the STP convergence time and maximize the network stability. Two possible techniques for STP internal timers management are evaluated. The presence of failures (either broken links or nodes) is also taken into account, in order to determine the proper STP parameters which guarantee connectivity recovery and convergence in all possible network scenarios. Some of the simulation results are also verified through an experimental testbed. Finally, the use of "transparent" switches is proposed as a solution to (i) speed convergence, (ii) increase the reaction capability to failures, and (iii) overcome the limitations, on the maximum number of sustainable nodes, imposed by the STP. In particular, this approach allows to extend the number of nodes in the network, still guaranteeing the possibility of incorporating VLANs.