Photonic Network Communications, 3:1/2, 161±171, 2001 # 2001 Kluwer Academic Publishers. Manufactured in The Netherlands. Effects of Optical Buffering on the Performance of Manhattan Street Networks Ayman G. Fayoumi, Anura P. Jayasumana Department of Electrical and Computer Engineering, Colorado State University, Fort Collins, CO 80523 E-mail: Ayman@engr.colostate.edu, Anura.Jayasumana@colostate.edu Received August 25, 2000; Revised October 30, 2000 Abstract. Multihop networks are strong candidates for the implementation of high-speed networks, ranging from back-plane networks for cluster computing to metropolitan-area networks. Besides using de¯ection routing for contention resolution, optical buffering may be used to enhance the performance of optical multihop networks and to reduce or even eliminate the need for optical-electrical conversions. The enhancements obtained by augmenting traditional MSN (Manhattan Street Networks) with optical buffering are evaluated. The MSN considered here is based on a novel 666 optical switching node with up to two ®ber delay loops. Impact of the parameters associated with optical buttering, such as the number of delay loops and the loop length, are discussed in detail. Keywords: multihop networks, photonic switching, optical networks, optical buffering, Manhattan-street networks, de¯ection routing 1 Introduction Multihop networks such as the Manhattan Street Network and the Shuf¯enet have received a lot of attention as potential candidates for high speed networks ranging from those for tightly coupled systems for cluster computing to networks spanning metropolitan areas [6,9,14,17]. When the nodes in such networks are implemented using electronics, the contention resolution is carried out using either store- and-forward techniques or de¯ection routing tech- niques. The former relies on random access memory, while the latter resolves the contentions by de¯ecting some of the contending packets to free links. When the network nodes are implemented optically, optical buffering provides a convenient mechanism to enhance the performance of these networks. Optical buffers are implemented using delay lines, i.e., ®xed length ®bers. Once a packet enters the delay line, it has to emerge from the other end after a ®xed amount of time. Thus they are not a direct replacement for memory buffers used in electronic implementations. Several designs of node architectures for use in multihop networks and/or photonic switches that incorporate optical buffering have appeared in recent literature [4,7,18]. However, not well understood are factors such as the impact on the network performance when optical buffering is used, and the complexity vs. performance tradeoffs. Optical buffering can impact these in two ways. First, it can be used to augment schemes such as de¯ection routing. Second, it can be used to reduce or even eliminate optical-electrical conversions of signals, thus signi®cantly reducing the node complexity and latency. In this paper, we evaluate the impact of augmenting Manhattan Street Networks (MSNs) using de¯ection routing with optical buffers compared to traditional implementations dealing with de¯ection routing only. A discrete event simulator is used to evaluate the performance of the Manhattan Street Network as an example of the multihop network system. The evaluated network is based on a novel, all-optical switching node architecture [16]. The main features of the multihop network are reviewed in Section 2 with emphasis on MSNs. Architecture and the main features of the developed all-optical MSN switching node are presented in Section 3. The con®guration and the contention resolution scheme of the simulated network are discussed in Section 4. The performance results are presented in Section 5.