i Chapter 1 STP-BASED NETWORKS: ANALYSIS AND DESIGN

In this work we analyze, through simulations, the performance of Spanning Tree Protocol (STP)-based Ethernet networks with ring and double ring topologies. In par-ticular, 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 con-vergence 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 param-eters 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) ac-celerate the STP convergence, (ii) increase the reaction capability to failures, and (iii) overcome the limitations, imposed by the STP, on the maximum sustainable number of nodes. In particular, this approach allows to extend the number of nodes in the network, still guaranteeing the possibility of incorporating VLANs. In order to evalu-ate the impact of failures in a realistic network, the Open Shortest Path First (OSPF) protocol and the Hot Standby Router Protocol (HSRP) are introduced in an STP-based network. This analysis shows that the use of OSPF protocol and the HSRP does not affect the STP performance, even if a longer delay is required in order to start the transmission of ping messages and a reduced reaction capability to node/link failures must be accounted for