Hybrid Media Access Protocols for a DSM System based on Optical WDM Networks

		       Krishna M. Sivalingam
		      Computer Science Division
		 Department of Mathematical Sciences
	      University of North Carolina at Greensboro
			 Greensboro, NC 27412

Scalable, hierarchical, all-optical Wavelength Division Multiplexed (WDM) networks for interconnection in distributed cluster-based computing systems have been recently considered. Hybrid access protocols combining reservation and pre-allocation have been studied for this type of network which supports a distributed shared memory (DSM) environment. The objectives of the protocols are reduced average latency per packet, support of broadcast/multicast, collisionless communication, and exploitation of inherent DSM traffic characteristics. This paper compares random and static access strategies on the control channel to establish reservation for data packets. Random access provides reduced packet latency under light traffic conditions and has simpler implementation. Static access is free of collisions and instability but has longer control cycle lengths. The performance of the network is analyzed through simulation models with varying system parameters such as number of nodes and channels. Dynamic schemes which switch between random and static access and vice-versa are also considered.