Upper Bound Analysis and Routing in Optical Benes Networks

Multistage Interconnection Networks (MIN) are popular in switching and communication applications. It has been used in telecommunication and parallel computing systems for many years. The new challenge facing optical MIN is crosstalk, which is caused by coupling two signals within a switching element. Crosstalk is not too big an issue in the Electrical Domain, but due to the stringent Bit Error Rate (BER) constraint, it is a big major concern in the Optical Domain. In this research dissertation, we will study the blocking probability in the optical network and we will study the deterministic conditions for strictly non-blocking Vertical Stacked Optical Benes Networks (VSOBN) with and without worst-case scenarios. We will establish the upper bound on blocking probability of Vertical Stacked Optical Benes Networks with respect to the number of planes used when the non-blocking requirement is not met. We will then study routing in WDM Benes networks and propose a new routing algorithm so that the number of wavelengths can be reduced. Since routing in WDM optical network is an NP-hard problem, many heuristic algorithms are designed by many researchers to perform this routing. We will also develop a genetic algorithm, simulated annealing algorithm and ant colony technique and apply these AI algorithms to route the connections in WDM Benes network

Simulated Annealing Routing and Wavelength Lower Bound Estimation on WDM Optical Multistage Networks

Multistage interconnection networks (MINs) are popular in switching and communication applications and have been used in telecommunication and parallel computing systems for many years. Crosstalk a major problem introduced by an optical MIN, is caused by coupling two signals within a switching element. We focus on an efficient solution to avoiding crosstalk by routing traffic through an N3N optical network to avoid coupling two signals within each switching element using wavelength-division multiplexing (WDM) and a time-division approach. Under the constraint of avoiding crosstalk, the interest is on realizing a permutation that uses the minimum number of passes for routing. This routing problem is an NP-hard problem. Many heuristic algorithms are already designed by researchers to perform this routing such as a sequential algorithm, a degree-descending algorithm, etc. The genetic algorithm is used successfully to improve the performance over the heuristic algorithms. The drawback of the genetic algorithm is its long running times. We use the simulated annealing algorithm to improve the performance of solving the problem and optimizing the result. In addition, a wavelength lower bound estimate on the minimum number of passes required is calculated and compared to the results obtained using heuristic, genetic, and simulated annealing algorithms. Many cases are tested and the results are compared to the results of other algorithms to show the advantages of simulated annealing algorithm

Optical architectures for high performance switching and routing

This thesis investigates optical interconnection networks for high performance switching and routing. Two main topics are studied. The first topic regards the use of silicon microring resonators for short reach optical interconnects. Photonic technologies can help to overcome the intrinsic limitations of electronics when used in interconnects, short-distance transmissions and switching operations. This thesis considers the peculiarasymmetric losses of microring resonators since they pose unprecedented challenges for the design of the architecture and for the routing algorithms. It presents new interconnection architectures, proposes modifications on classical routing algorithms and achieves a better performance in terms of fabric complexity and scalability with respect to the state of the art. Subsequently, this thesis considers wavelength dimension capabilities of microring resonators in which wavelength reuse (i.e. crosstalk accumulation) presents impairments on the system performance. To this aim, it presents different crosstalk reduction techniques, a feasibility analysis for the design of microring resonators and a novel wavelength-agile routing matrix. The second topic regards flexible resource allocation with adaptable infrastructure for elastic optical networks. In particular, it focus on Architecture on Demand (AoD), whereby optical node architectures can be reconfigured on the fly according to traffic requirements. This thesis includes results on the first flexible-grid optical spectrum networking field trial, carried out in a collaboration with University of Essex. Finally, it addresses several challenges that present the novel concept AoD by means of modeling and simulation. This thesis proposes an algorithm to perform automatic architecture synthesis, reports AoD scalability and power consumption results working under the proposed synthesis algorithm. Such results validate AoD as a flexible node concept that provides power efficiency and high switching capacity

Symmetric rearrangeable networks and algorithms

A class of symmetric rearrangeable nonblocking networks has been considered in this thesis. A particular focus of this thesis is on Benes networks built with 2 x 2 switching elements. Symmetric rearrangeable networks built with larger switching elements have also being considered. New applications of these networks are found in the areas of System on Chip (SoC) and Network on Chip (NoC). Deterministic routing algorithms used in NoC applications suffer low scalability and slow execution time. On the other hand, faster algorithms are blocking and thus limit throughput. This will be an acceptable trade-off for many applications where achieving ”wire speed” on the on-chip network would require extensive optimisation of the attached devices. In this thesis I designed an algorithm that has much lower blocking probabilities than other suboptimal algorithms but a much faster execution time than deterministic routing algorithms. The suboptimal method uses the looping algorithm in its outermost stages and then in the two distinct subnetworks deeper in the switch uses a fast but suboptimal path search method to find available paths. The worst case time complexity of this new routing method is O(NlogN) using a single processor, which matches the best known results reported in the literature. Disruption of the ongoing communications in this class of networks during rearrangements is an open issue. In this thesis I explored a modification of the topology of these networks which gives rise to what is termed as repackable networks. A repackable topology allows rearrangements of paths without intermittently losing connectivity by breaking the existing communication paths momentarily. The repackable network structure proposed in this thesis is efficient in its use of hardware when compared to other proposals in the literature. As most of the deterministic algorithms designed for Benes networks implement a permutation of all inputs to find the routing tags for the requested inputoutput pairs, I proposed a new algorithm that can work for partial permutations. If the network load is defined as ρ, the mean number of active inputs in a partial permutation is, m = ρN, where N is the network size. This new method is based on mapping the network stages into a set of sub-matrices and then determines the routing tags for each pair of requests by populating the cells of the sub-matrices without creating a blocking state. Overall the serial time complexity of this method is O(NlogN) and O(mlogN) where all N inputs are active and with m < N active inputs respectively. With minor modification to the serial algorithm this method can be made to work in the parallel domain. The time complexity of this routing algorithm in a parallel machine with N completely connected processors is O(log^2 N). With m active requests the time complexity goes down to (logmlogN), which is better than the O(log^2 m + logN), reported in the literature for 2^0.5((log^2 -4logN)^0.5-logN)<= ρ <= 1. I also designed multistage symmetric rearrangeable networks using larger switching elements and implement a new routing algorithm for these classes of networks. The network topology and routing algorithms presented in this thesis should allow large scale networks of modest cost, with low setup times and moderate blocking rates, to be constructed. Such switching networks will be required to meet the bandwidth requirements of future communication networks

Parallel routing and wavelength assignment for optical multistage interconnection networks

Multistage interconnection networks (MINs) are among the most efficient switching architectures in terms of the number of switching elements (SEs) used. For op-tical MINs (OMINs), two I/O connections with neigh-boring wavelengths cannot share a common SE due to crosstalk. In this paper, we focus on the wavelength di-lation approach, in which the I/O connections shar-ing a common SE will be assigned different wavelengths with enough wavelength spacing. We first study the per-mutation capacity of OMINs, then propose fast par-allel routing and wavelength assignment algorithms for OMINs. By applying our permutation decomposi-tion and graph coloring techniques, the proposed algo-rithms can route any permutation without crosstalk in wavelength-rearrangeable space-strict-sense Banyan net-works and wavelength-rearrangeable space-rearrangeable Benes networks in polylogarithmic time using a linear num-ber of processors. 1

Crosstalk-free Conjugate Networks for Optical Multicast Switching

High-speed photonic switching networks can switch optical signals at the rate of several terabits per second. However, they suffer from an intrinsic crosstalk problem when two optical signals cross at the same switch element. To avoid crosstalk, active connections must be node-disjoint in the switching network. In this paper, we propose a sequence of decomposition and merge operations, called conjugate transformation, performed on each switch element to tackle this problem. The network resulting from this transformation is called conjugate network. By using the numbering-schemes of networks, we prove that if the route assignments in the original network are link-disjoint, their corresponding ones in the conjugate network would be node-disjoint. Thus, traditional nonblocking switching networks can be transformed into crosstalk-free optical switches in a routine manner. Furthermore, we show that crosstalk-free multicast switches can also be obtained from existing nonblocking multicast switches via the same conjugate transformation.Comment: 10 page

A new scheme to realize crosstalk-free permutations in optical MINs with vertical stacking

©2002 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Vertical stacking is an alternative for constructing nonblocking multistage interconnection networks (MINs). In this paper, we study the crosstalk-free permutation in rearrangeable, self-routing Banyan-type optical MINs built on vertical stacking and propose a new scheme for realizing permutations in this class of optical MINs crosstalk-free. The basic idea of the new scheme is to classify permutations into permutation classes such that all permutations in one class share the same crosstalk-free decomposition pattern. By running the Euler-Split based crosstalk-free decomposition only once for a permutation class and applying the obtained crosstalk-free decomposition pattern to all permutations in the class, crosstalk-free decomposition of permutations can be realized in a more efficient way. We show that the number of permutations in a permutation class is huge, enabling the average time complexity of the new scheme to realize a crosstalk-free permutation in an N by N network to be reduced to O(N) from previously O(NlogN).Xiaohong Jiang, Hong Shen, Md. Mamun-ur-Rashid Khandker, Susumu Horiguch

Providing quality of service over high speed electronic and optical switches

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 235-239).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.In a network, multiple links are interconnected by means of switches. A switch is a device with multiple input and output links, and its job is to move data from the input links to the output links. In this thesis, we focus on a number of fundamental issues concerning the quality of service provided by electronic and optical switches. We discuss various mechanisms that enable the support of quality of service requirements. In particular, we explore fundamental limitations of current high speed packet switches and develop new techniques and architectures that make possible the provision of certain service guarantees. We then study optical wavelength switches and illustrate how similar ideas can be applied in a manner consistent with the current state of optical switching technology. First, we focus on providing rate guarantees over packet switches. We develop a method called rate quantization which converts the set of desired rates into a certain discrete set such that the quality of service guarantees can be greatly improved with a small resource speedup. Moreover, quantization simplifies rate provisioning for dynamically changing traffic demands since it allows service opportunities for different input output link pairs to be scheduled with minimal dependence. We illustrate an isomorphism between packet switch schedulers and Clos networks to develop such schedulers.(cont.) Next, we evaluate the amount of resource speedup necessary for single stage switches to support multicast rates. This speedup limits the scalability of a single stage multicast switch a great deal. We present an in depth study of multistage switches and propose a number of architectures, along with associated routing and scheduling algorithms. We illustrate how the presence of multiple paths between input output pairs can be exploited to improve the performance of a switch and simplify the scheduling algorithms. Some of our architectures are capable of providing multicast rate guarantees without a need for a resource speedup. We extend our results on switch schedulers and use them for providing service guarantees over optical wavelength switches. We will take the limitations of the optical crossconnects and unavailability of optical memory technology into account, and modify the procedure we developed for electronic switches to make them suitable for various optical wavelength switches. These results will provide understanding of when to move optical switching closer to the end users for an efficient utilization of resources in networks with both optical and electronic technologies.by Can Emre Koksal.Ph.D

Blocking performance of extended pruned vertically stacked optical banyan structure under different link failure conditions

The blocking performance of extended pruned vertically stacked optical banyan (VSOB) networks under different link failure conditions has been analyzed in this paper. We applied plane fixed routing with linear search and plane fixed routing with random search algorithms to route the optical data through the network in our simulation. Our simulation results show that adding one or two extra planes to the pruned VSOB network reduces the blocking probability significantly. Beyond two extra planes, the decrease of blocking probability is not so significant. A close approximation of the minimum number of planes required to make the extended pruned vertically stacked optical banyan networks nonblocking has been presented