WDM Media Access Protocol for Project LIGHTNING1

This paper presents the design and analysis of a media access protocol implemented in LIGHTNING, an optical WDM network testbed that has been designed for high-performance supercomputer interconnection. The architecture is based on a dynamically reconfigurable hierarchical WDM network to interconnect a large number of supercomputers and create a distributed shared memory (DSM) environment. This paper describes the network media access protocol, called LiteMAC, based on a single tunable transmitter and single tunable receiver (TT-TR) per node which exploits the bimodal traffic characteristics of a DSM system. The primary objectives of the protocol design are reduced average latency per packet, support of broadcast/multicast, and support of collision-less communication. The performance of the protocol has been studied using three means: mathematical analysis, discrete event simulation, and experimental evaluation. Performance is studied in terms of average latency and channel utilization is analyzed for varying system characteristics such as number of nodes, channels, and levels. The testbed was used to demonstrate protocol feasibility and to measure packet latency.