LIGHTNING is a dynamically reconfigurable WDM network testbed project for supercomputer interconnection. This paper describes a hierarchical WDM-based optical network testbed that is being constructed to interconnect a large number of supercomputers and to create a distributed shared memory environment. The objective of the hierarchical architecture is to achieve scalability yet avoiding the requirement of multiple wavelength tunable devices per node. Furthermore, single-hop all-optical communication is achieved: a packet remains in the optical form from source to destination and does not require intermediate routing. The wavelength multiplexed hierarchical structure features wavelength channel re-use at each level, allowing scalability to very large system sizes. It partitions the traffic between different levels of the hierarchy without electronic intervention in a combination of wavelength- and space-division multiplexing. A significant advantage of this approach is its ability to dynamically vary the bandwidth provided to different levels of the hierarchy. Each node in LIGHTNING receives traffic on n channels in an n-level hierarchy, one channel for each level. Each node monitors the traffic intensities on each channel and can detect any temporal or spatial shift in traffic balance. LIGHTNING can dynamically reconfigure to balance the traffic at each level by moving wavelengths associated with each level up or down depending on need. Bandwidth re-allocation is completely decentralized-any node can initiate it, achieving highly fault tolerant system behavior. This paper describes the system architecture, network and memory interface, and the optical devices that have been developed in this project.

The above paper by L. Bhuyan and D.P. Agrawal (1984) described a hierarchical, all-optical wavelength division multiplexed (WDM) network that is being built to support the communication requirements of a large distributed shared memory system. Dynamically adaptable bandwidth allocation is supported, both within and between levels of the hierarchy, and is highly scalable through wavelength re-use at each hierarchical level. The mixed radix scheme introduced was used for processor numbering, but was not specified. The system was described in term of a time multiplexed access protocol, generalized to the multichannel WDM environment, which has static slot assignment that provides excellent throughput but long latencies due to cycle synchronization. The actual system implementation will use a hybrid WDMA strategy, which is collisionless, provides low latency support, dynamic bandwidth allocation within a hierarchical level, and a fast reliable broadcast.>

This paper introduces a hierarchical optical structure for processor interconnection and evaluates its performance. The architecture is based on wavelength division multiplexing (WDM) which enables multiple multi-access channels to be realized on a single optical fiber. The objective of the hierarchical architecture is to achieve scalability yet avoid the requirement of multiple wavelength tunable devices per node as with the WDM-based hypercube interconnection scheme. Furthermore, single-hop communication is achieved: a packet remains in the optical form from source to destination and does not require cross dimensional intermediate routing. The wavelength multiplexed hierarchical structure features wavelength channel re-use at each level, allowing scalability to very large system sizes. It employs acousto-optic tunable filters in conjunction with passive couplers to partition the traffic between different levels of the hierarchy without electronic intervention. A significant advantage of the proposed structure is its ability to dynamically vary the bandwidth provided to different levels of the hierarchy. The architecture is compared to a wavelength-flat architecture in terms of physical and performance scalability.>

Introduces two hierarchical optical structures for processor interconnection and compares their performance through analytic models and discrete-event simulation. Both architectures are based on wavelength division multiplexing (WDM) which enables multiple multi-access channels to be realized on a single optical fiber. The objective of the hierarchical architectures is to achieve scalability yet avoid the requirement of multiple wavelength tunable devices per node. Furthermore, both hierarchical architectures are single-hop: a packet remains in the optical form from source to destination and does not require cross dimensional intermediate routing.>