ARCHITECTURAL ISSUES OF ATM BASED CONNECTIONLESS OVERLAY NETWORK

Connectionless service such as SMDS, or its European equivalent CBDS, can be provided by an ATM network by building a separate connectionles s overlay network (CLON) on top of the ATM bearer service. A CLON is c omposed of a number of connectionless servers, CLSs, which provide the routing function, connected by semipermanent virtual paths (VPs). In this paper, architectural issues related to the design of a CLON are s tudied. In particular, we address the question of the optimal number o f CLSs and their interconnection topology, assuming the underlying ATM network and the mean connectionless traffic load are known. The objec tive of the design process is to meet given design criteria with minim um costs. The QoS requirements of the SMDS/CBDS service are briefly re viewed and a simple cost model for the CLON network is given. The dime nsioning of the logical links is also considered. Then the design proc ess to find the optimal solution for the whole network is outlined. A simplified procedure was applied in numerical studies of the topologic al optimization. In order to find the general dependence of the optima l number of CLSs on the size of the network and other network paramete rs, the optimization procedure was applied to a large number of sample ATM networks, generated by an algorithm which is briefly described. R esults from these studies are presented and discussed.