Best-E ort Bandwidth Reservation in High Speed LANs using Wormhole Routing

Current quality of service schemes require switching nodes to identify and manipulate packets within large switch bu ers. These methods are e ective for networks with switching nodes that contain su cient resources, such as in ATM networks. However, in wormhole routing networks like Myrinet, the emphasis on providing low latency and high link speeds at a low cost precludes the use of intelligent switches with large bu ers. In this paper, we present a simple scheme that provides \best e ort" bandwidth reservation to delay sensitive tra c in a wormhole routing LAN. The idea behind this scheme is that low priority messages are segmented into smaller packets before transmission into the network while high priority messages are left unsegmented. Switches employ round robin scheduling to resolve streams contending for the same output port. Consequently, larger packets are given more bandwidth than segmented tra c. We demonstrate this idea via simulation and present results relating the optimal low priority packet length to the distance the packet must travel to reach its destination.