ExpressMAN: Exploiting Traffic Locality in Expressnet

ExpressMAN is a metropolitan area network architecture which connects users grouped in different clusters. It retains all the positive features of LAN's, but in addition, allows for parallel transmission of local traffic. The overall network structure is halfway between a linear bus and a two-level hierarchical structure in which several subnetworks are connected by a backbone network. However, it does not need complex routing facilities like bridges. Based on the Expressnet access mechanism, it can be dynamically configured either as a unique bus or as several different local buses which allow the circulation of long distance and local trains, respectively. Routing is performed by the transmitting stations choosing the correct train. Local communications can take the bandwidth not used by long distance trains, and thus increase bandwidth efficiency by means of parallel transmissions. In this paper, the performance of ExpressMAN is evaluated and compared to that achieved by the aforementioned two-level structure based on Express networks. Although the Expressnet mechanism has been chosen as the simplest and most efficient mechanism available for LAN's the principle underlying ExpressMAN could be applied to other token schemes such as the token ring.