In this paper, we study the blocking probabilities in a wavelength division multiplexing-based asynchronous bufferless optical burst switch equipped with a bank of tuneable wavelength converters that is shared per output link. The site of this bank is generally chosen to be less than the number of wavelengths on the link because of the relatively high cost of wavelength converters using current technologies; this case is referred to as partial wavelength conversion in the literature. We present a probabilistic framework for exactly calculating the blocking probabilities. Burst durations are assumed to be exponentially distributed. Burst arrivals are first assumed to be Poisson and later generalized to the more general phase-type distribution. Unlike existing literature based on approximations and/or simulations, we formulate the problem as one of finding the steady-state solution of a continuous-time Markov chain with a block tridiagonal infinitesimal generator. We propose a numerically efficient and stable solution technique based on block tridiagonal LU factorizations. We show that blocking probabilities can exactly and efficiently be found even for very large systems and rare blocking probabilities. Based on the results of this solution technique, we also show how this analysis can be used for provisioning wavelength channels and converters.

Network survivability is one of the most important issues in the design of optical WDM networks. In this work we study the problem of survivable routing of a virtual topology on a physical topology with shared risk link groups (SRLG). The survivable virtual topology routing problem against single-link failures in the physical topology is proved to be NP-complete in E. Modiano and A. Narula-Tam, May 2002. We prove that survivable virtual topology routing problem against SRLG/node failures is also NP-complete. We present an improved integer linear programming (ILP) formulation (in comparison to E. Modiano and A. Narula-Tam, May 2002) for computing the survivable routing under SRLG/node failures. Using an ILP solver, we computed the survivable virtual topology routing against link and SRLG failures for small and medium sized networks efficiently. As even our improved ILP formulation becomes intractable for large networks, we present a congestion-based heuristic and a tabu search heuristic (which uses the congestion-based heuristic solution as the initial solution) for computing survivable routing of a virtual topology. Our experimental results show that tabu search heuristic coupled with the congestion based heuristic (used as initial solution) provides fast and near-optimal solutions.

In-band crosstalk has been widely considered as a major transmission impairment that significantly impacts the BER (bit error rate) performance of lightpaths in circuit-switched all-optical wavelength-routed networks. Such crosstalk usually occurs when multiple lightpaths occupying identical or adjacent wavelengths pass through an optical crossconnect node. Traditional WA (wavelength assignment) schemes pay little regard to the physical layer QoS (quality of service), and hence cannot provide optimized network performance in practice. In this paper, we propose four crosstalk-aware WA algorithms as variations of the well-known first-fit, random-pick, most-used and least-used schemes, with the crosstalk factor taken into consideration. Simulation results show that, independent of the network amplifier placement and the traffic, our WA algorithms can successfully suppress the in-band crosstalk throughout the network, and significantly decrease BER blocking rate.

In this paper, we consider the problem of routing and wavelength assignment (RWA) of fault-tolerant scheduled lightpath demands (FSLDs) in all optical wavelength division multiplexing (WDM) networks under single component failure. In scheduled traffic demands, besides the source, destination, and the number of lightpath demands between a node-pair, their set-up and tear-down times are known, in this paper, we develop integer linear programming (ILP) formulations for dedicated and shared scheduled end-to-end protection schemes under single link/node failure for scheduled traffic demand with two different objective functions: 1) minimize the total capacity required for a given traffic demand while providing 100% protection for all connections; and 2) given a certain capacity, maximize the number of demands accepted while providing 100% protection for accepted connections. The ILP solutions schedule both the primary and end-to-end protection routes and assign wavelengths for the duration of the traffic demands. As the time disjointness that could exist among fault-tolerant scheduled lightpath demands is captured in our formulations, it reduces the amount of global resources required. The numerical results obtained from CPLEX indicate that dedicated scheduled (with set-up and tear-down times) protection provides significant savings (up to 33 %) in capacity utilization over dedicated conventional (without set-up and tear-down times) end-to-end protection scheme; shared scheduled protection provides considerable savings (up to 21 %) in capacity utilization over shared conventional end-to-end protection schemes. Also the numerical results indicate that shared scheduled protection achieves the best performance followed by dedicated scheduled protection scheme, and shared conventional end-to-end protection in terms of the number of requests accepted, for a given network capacity.

We investigate a call admission control (CAC) mechanism to provide fairness control and service differentiation in a WDM network with grooming capabilities. A WDM grooming network can handle different classes of traffic streams which differ by their bandwidth requirements. We assume that for each class, call interarrival and holding times are exponentially distributed. Using a Markov decision process approach, an optimal CAC policy is derived to provide fairness in the network. The policy iteration algorithm is used to numerically compute the optimal policy. Furthermore, we propose a heuristic decomposition algorithm with lower computational complexity and very good performance. Simulation results compare the performance of our proposed policy, with that of complete sharing and complete partitioning policies. Comparisons show that our proposed policy provides the best performance in most cases. Although this approach is motivated by WDM networks, it may be deployed to determine the optimal resource allocation in many problems in wireless and wired telecommunications systems.

Advances in optical data transmission and optical signal routing have caused wide expectation for optical networks to form tomorrow's backbone transport. One attractive feature of these networks is the ability to reconfigure the logical topology of the network seen by higher layers with comparative ease and speed by reconfiguring optical switches, without the need to modify the physical topology of the network. On the other hand, with the current mismatch of bandwidth available from individual wavelength channels and typical bandwidth demands, it is also widely recognized that grooming of subwavelength traffic into the full-wavelength channels is an indispensable component of optical network design. The topic of reconfiguration in optical networks that carry subwavelength traffic has received comparatively little attention. In this paper, we consider this problem. Our main contributions are as follows. We discuss the common basis on which grooming effectiveness and reconfiguration efficiency can be considered, and develop a reconfiguration cost function in keeping with this consideration. We formulate the joint problem of reconfiguration and grooming precisely, and offer a heuristic as well as an exact solution method to solve this problem. In offering numerical simulation results for our algorithms, we make the important observation that a disjoint sequential consideration of the two problems leads to solutions that are very inefficient in the joint sense.

As high capacity all-optical networks and WDM technologies advance and merge together, aggregating low-speed traffic streams onto high-speed wavelengths becomes more critical. Efficient aggregation techniques, known as traffic grooming, allow higher bandwidth utilization and can reduce request blocking probability. These algorithms can also result in lower network cost in terms of electronic switching. In this paper we focus on traffic grooming in WDM mesh networks with dynamic traffic patterns. We offer two new grooming concepts called lightpath dropping and lightpath extension. These concepts are based on an alternative node architecture in which incoming optical signals can be dropped at a node, while optically continuing to the next node. Based on these concepts, we develop several grooming algorithms and study them under various network objectives. We also compare their performance with previously proposed lightpath-based grooming algorithms. Through extensive simulation results we show that our proposed approaches lead to lower request blocking probability and lower average number of logical hops when the number of transceivers per node is limited.

The optical connections (lightpaths) offered to the client by optical networks have large capacities. On the other hand, the client traffic flows require smaller and heterogeneous bandwidths. Due to this bandwidth gap, client traffic flows are aggregated onto lightpaths to improve network utilization and reduce cost, which is called traffic grooming. In this paper, we develop an analytical model using the single-service reduced load approximation to compute traffic loss probabilities in grooming of dynamic traffic. The model can address arbitrary alternate routing, and arbitrary wavelength conversion in the optical network. We have compared this model with a previous work that uses the multi-service reduced load approximation, with regard to computation time and calculated blocking probabilities. The results obtained by the single-service model are very close to those by the multi-service model, and the computation time can be significantly improved. On the other hand, the results calculated by the (both single and multi-service) analyses match those obtained by the simulation.

Browse Conference Publications > Broadband Networks, 2004. Bro ... Performance comparison of guided-wave architectures for space-division photonic switching Full text access may be available To access full text, please use your member or institutional sign in. Learn more about subscription options Already purchased? View now Forgot Username/Password? Forgot Institutional Username or Password? Athens/Shibboleth This paper appears in: Broadband Networks, 2004. BroadNets 2004. Proceedings. First International Conference on Date of Conference: 25-29 Oct. 2004 Author(s): Savastano, L. CoreCom, Milan, Italy Maier, G. ; Martinelli, M. ; Pattavina, A. Page(s): 202 - 211 Product Type: Conference Publications Available Formats Non-Member Price Member Price PDF US€ 31,00 US€ 10,00 ABSTRACT The paper presents and compares various unicast nonblocking architectures to be used into space-domain photonic switching networks. All the analyzed architectures have been evaluated and compared considering a possible physical implementation based on guided-wave structures realized with integrated optics technology. Some properties including number of switching elements required, blocking performance, number of waveguide crossovers, system attenuation, and signal-to-noise ratio are evaluated and analyzed. The main purpose of this work is to review the state-of-the-art of optical guided-wave space-switching architectures and to provide a relevant set of technical elements useful in the selection of architectures to be used in all-optical cross-connect implementation.

Advances in optical WDM technology have paved the way for high-capacity wavelength channels capable of carrying information at Gb/s rates. However, with current traffic streams requiring only a fraction of a wavelength's bandwidth, it becomes necessary to groom these independent low rate traffic streams on to higher capacity wavelength channels. An all-optical approach to grooming is to allow many connections to time-share a wavelength. Accordingly, in a TDM wavelength routing network, the establishment of a connection requires the assignment of time slots in addition to routing and wavelength assignment. One of the primary challenges in such networks is the need for quick reconfiguration at the routing nodes. In this paper, we investigate the effects of switch reconfigurability, wavelength conversion and time slot interchangers (TSIs) on the blocking performance of connections with multiple rates. Heuristics for time slot assignment that consider constraints imposed by six different node architectures are proposed, and the blocking performance of the TDM wavelength routing network is evaluated through simulations. Results indicate that limited reconfigurability at the nodes is sufficient to attain the performance obtained with full reconfigurability, especially when connections occupy only a small fraction of the wavelength capacity. Furthermore, the blocking performance is not seen to benefit significantly with the introduction of wavelength converters and TSIs, thus signifying that the improvement in blocking is largely dependent on the switch reconfigurability at the nodes.