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Routing Foreseeable Lightpath Demands Using a Tabu Search Metaheuristic
 in Procs. of GLOBECOM 2002
, 2002
"... In this paper we investigate the problem of routing a set of lightpath demands for which the setup and teardown dates are known. We call this type of requests Foreseeable Lightpath Demands or FLDs. In a transport network, FLDs correspond, for example, to clients' requests for preprovisioned ..."
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Cited by 18 (4 self)
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In this paper we investigate the problem of routing a set of lightpath demands for which the setup and teardown dates are known. We call this type of requests Foreseeable Lightpath Demands or FLDs. In a transport network, FLDs correspond, for example, to clients' requests for preprovisioned bandwidth capacity such as fixedbandwidth pipes for bulk data transfers during the night, extra VPN bandwidth used during peak office working time, etc. Since in some cases the FLDs are not all simultaneous in time, it is possible to reuse physical resources to realize timedisjoint demands. We propose a routing algorithm that takes into account this property to minimize the number of required WDM channels in the physical links of the network. The gain (in terms of saved WDM channels) provided by the algorithm, when compared to a shortest path routing strategy, depends both on the spatial and temporal structure of the set of traffic demands and on the structure of the physical network. The routing problem is formulated as a spatiotemporal combinatorial optimization problem. A Tabu Search metaheuristic algorithm is developed to solve this problem. I.
Diverse Routing of Scheduled Lightpath Demands in an Optical Transport Network
 4th Workshop on Design of Reliable Computer Networks
, 2003
"... This article addresses the problem of defining working and protection paths for Scheduled Lightpath Demands (SLDs) in an optical transport network. An SLD is a demand for a set of lightpaths (connections), defined by a tuple (s, d, n, #, #), where s and d are the source and destination nodes of the ..."
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Cited by 12 (2 self)
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This article addresses the problem of defining working and protection paths for Scheduled Lightpath Demands (SLDs) in an optical transport network. An SLD is a demand for a set of lightpaths (connections), defined by a tuple (s, d, n, #, #), where s and d are the source and destination nodes of the lightpaths, n is the number of requested lightpaths and #, # are the setup and teardown dates of the lightpaths. The problem is formulated as a combinatorial optimization problem where the objective is to minimize the number of channels required to instantiate the lightpaths. Two techniques are used to achieve this goal: channel reuse and backupmultiplexing. The former consists of assigning the same channel (either working or spare) to several lightpaths, provided that these lightpaths are not simultaneous in time. The latter consists of sharing a spare channel among multiple lightpaths. A spare channel cannot be shared if two conditions hold: a) the working paths of these lightpaths have at least one span in common and b) these lightpaths are simultaneous in time. In the other cases, the spare channel can be shared. We propose a Simulated Annealing (SA) based algorithm to find approximate solutions to this optimization problem since finding exact solutions is computationally intractable. The results show that backupmultiplexing improves the utilization of channels but requires significant computing capacity. Under a fixed computing capacity budget, the technique is useful in cases where there is little time disjointness among SLDs.
Fast Exact ILP Decompositions for Ring RWA
, 2010
"... WDM rings are now capable of supporting more than 100 wavelengths over a single fiber. Conventional link and path formulations for the RWA problem are inefficient due to the inherent symmetry in wavelength assignment and the fact that the problem size increases fast with the number of wavelengths. ..."
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Cited by 11 (9 self)
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WDM rings are now capable of supporting more than 100 wavelengths over a single fiber. Conventional link and path formulations for the RWA problem are inefficient due to the inherent symmetry in wavelength assignment and the fact that the problem size increases fast with the number of wavelengths. Although a formulation based on maximal independent sets (MIS) does not have these drawbacks, it suffers from the exponential growth in the number of variables with the increasing network size. We develop a new ILP formulation based on the key idea of partitioning the path set and representing the maximal independent sets in the original network using the independent sets calculated in each of these partitions. This exact decomposition trades off the number of variables with the number of constraints and, as a result, achieves a much better scalability in terms of network dimension. Numerical results on ring networks of various sizes demonstrate that this new ILP decomposition achieves several orders of magnitude decrease in running time compared to existing formulations. Our main contribution is a novel and extremely fast technique to obtain, in a few seconds using commodity CPUs, optimal solutions to instances of maximum size SONET rings with any number of wavelengths; such instances cannot be tackled with classical formulations without vast investments in computational resources and time.
Dynamic scheduling of network resources with advance reservations in optical grids
"... Advance reservation of lightpaths in Grid environments is necessary to guarantee QoS and reliability. In this paper, we have evaluated and compared several algorithms for dynamic scheduling of lightpaths using a flexible advance reservation model. The main aim is to find the best scheduling policy f ..."
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Advance reservation of lightpaths in Grid environments is necessary to guarantee QoS and reliability. In this paper, we have evaluated and compared several algorithms for dynamic scheduling of lightpaths using a flexible advance reservation model. The main aim is to find the best scheduling policy for a Grid network resource manager that improves network utilization and minimizes blocking. The scheduling of lightpaths involve both routing and wavelength assignment. Our simulation results show that minimum cost adaptive routing where link costs are determined by the current and future usage of the link provides the minimum blocking. For wavelength assignment, we have used a scheme that reduces fragmentation by minimizing unused gaps. We have also analyzed approaches for failure recovery and resource optimization. 1
Static Routing and Wavelength Assignment for Multicast Advance Reservation in AllOptical WavelengthRouted WDM Networks
"... In this paper we introduce and motivate the static multicast advance reservation (MCAR) problem for alloptical wavelengthrouted WDM networks. Under the advanced reservation traffic model, connection requests specify their start time to be some time in the future and also specify their holding time ..."
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In this paper we introduce and motivate the static multicast advance reservation (MCAR) problem for alloptical wavelengthrouted WDM networks. Under the advanced reservation traffic model, connection requests specify their start time to be some time in the future and also specify their holding times. We investigate the static MCAR problem where the set of advance reservation requests is known ahead of time. We show the problem is NPcomplete, formulate the problem mathematically as an integer linear program, and develop three efficient heuristics, seqRWA, ISH, and SA, to solve the problem for practical size networks. We also introduce a theoretical lower bound on the number of wavelengths required. To evaluate our heuristics we compare the results to the ILP for small networks and run simulations over realworld, large scale networks. We find the SA heuristic provides close to optimal results compared to the ILP for our smaller networks, and up to a 33 % improvement over seqRWA and up to a 22 % improvement over ISH on realistic networks. SA provides, on average, solutions 1.51.8x times the cost given by our conservative lower bound on large networks.
Scheduled virtual topology design under periodic traffic in transparent optical networks
 in Proceedings, IEEE BroadNets, 1416 2009
"... Abstract—This paper investigates offline planning and scheduling in transparent optical networks for a given periodic traffic demand. The main objective is to minimize the number of transceivers needed which make up for the main network cost. We call this problem “Scheduled Virtual Topology Design ” ..."
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Abstract—This paper investigates offline planning and scheduling in transparent optical networks for a given periodic traffic demand. The main objective is to minimize the number of transceivers needed which make up for the main network cost. We call this problem “Scheduled Virtual Topology Design ” and consider two variants: nonreconfigurable and reconfigurable equipment. We formulate both problems as exact MILPs (Mixed Integer Linear Programs). Due to their high complexity, we propose a more scalable tabu search heuristic approach, in conjunction with smaller MILP formulations for the associated subproblems. The main motivation of our research efforts is to assess the benefits of using reconfigurable equipment, realized as a reduction in the number of required transceivers. Our results show that the achieved reductions are not very significant, except for cases with large network loads and high traffic variability. Index Terrms — Alloptical networks, virtual topology design, multilayer optimization, scheduling, tabu search. I.
A Fast PathBased ILP Formulation for Offline RWA in Mesh Optical Networks
"... Abstract—RWA is a fundamental problem in the design and control of optical networks. We introduce the concept of symmetric RWA solutions and present a new ILP formulation to construct optimally such solutions. The formulation scales to mesh topologies representative of backbone and regional networks ..."
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Abstract—RWA is a fundamental problem in the design and control of optical networks. We introduce the concept of symmetric RWA solutions and present a new ILP formulation to construct optimally such solutions. The formulation scales to mesh topologies representative of backbone and regional networks. Numerical results demonstrate that the new formulation achieves a decrease of up to two orders of magnitude in running time compared to existing formulations. In particular, optimal solutions for topologies up to 20 nodes can be obtained within minutes using commodity CPUs, and larger networks can be solved in reasonable time. Our approach significantly lowers the barrier to entry in fully exploring the solution space of optical network design and in investigating the sensitivity of design decisions to forecast demands via extensive “whatif ” analysis. Such analysis cannot be carried out currently without large investments in computational resources and time. I.
PHOTO: An Efficient SharedPathProtection Strategy Based on ConnectionHoldingTime Awareness
"... Abstract—Recent trends in bandwidth markets show that customers are tending to ask providers for a large bandwidth but for a limited amount of time to support new shortterm bandwidthhungry applications. In order to meet these new requirements, progress in network technologies (fast and reconfigurab ..."
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Cited by 5 (1 self)
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Abstract—Recent trends in bandwidth markets show that customers are tending to ask providers for a large bandwidth but for a limited amount of time to support new shortterm bandwidthhungry applications. In order to meet these new requirements, progress in network technologies (fast and reconfigurable switching equipment) and protocols [such as generalized multiprotocol label switching (GMPLS) and automatically switched optical network (ASON)] is paving the road towards flexible optical transport networks in which leasable circuits could be set up and released on a shortterm basis. As a result, for dynamic traffic, the holding time of connection requests can be known in advance. The authors propose to exploit knowledge of connection holding time to design an efficient algorithm, called PHOTO, for the dynamic provisioning of sharedpathprotected connections in optical mesh networks. The core idea of the proposal consists of exploiting the knowledge of the holding time of connection requests to minimize resource overbuild (RO) due to backup capacity and hence achieve resource–usage efficiency. For a typical US nationwide network, savings on RO of up to 10 % were obtained for practical scenarios compared to a holdingtimeunaware, but otherwise sharedpathefficient, approach. Index Terms—Dynamic traffic, fault management, holding time, lightpath, optical network, resource overbuild, sharedpath protection, WDM. I.
Vokkarane, “Multicast overlay for highbandwidth applications over optical WDM networks
"... Abstract—Multicast communication in wavelength division multiplexed (WDM) networks is traditionally supported by the assumption that the optical crossconnects are multicast capable, i.e., they are capable of switching an incoming signal to more than one output interface. A naïve method of supporting ..."
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Abstract—Multicast communication in wavelength division multiplexed (WDM) networks is traditionally supported by the assumption that the optical crossconnects are multicast capable, i.e., they are capable of switching an incoming signal to more than one output interface. A naïve method of supporting this functionality in a multicastincapable (MI) environment is by creating a virtual topology consisting of lightpaths from the multicast source to each destination of the multicast session. For large sets of multicast requests, however, the network bandwidth consumed by such a scheme may become unacceptable due to the unicasting nature of the lightpaths. We refer to this method as achieving multicast via WDM unicast (MVWU). To support users ’ multicast requests (from higher electronic layers) in MI networks, we propose two overlay solutions: drop at member node (DMN) and drop at any node (DAN). In these solutions, we achieve multicasting by creating a set of lightpath routes (possibly multiple hops) in the overlay layer from the source node of a request to each destination member. In the DMN case, we allow a lightpath route to originate/terminate only at source and destination members of a request, whereas in the DAN model we impose no such restrictions. We first consider a static traffic model, wherein the set of multicast requests is known ahead of time, and present integer linear programs (ILPs) to solve these problems (MVWU, DMN, and DAN) with the goal of minimizing the total number of wavelengths required to service the set. We also present an efficient heuristic and compare its performance to the ILP for a small network, and run simulations over realworld, largescale networks. Moreover, we present lower bounds to calculate the minimum number of wavelengths required by the DMN and DAN models. Finally, we evaluate the performance of the heuristic (minimization of the number of wavelengths) under a dynamic traffic scenario and also evaluate the blocking performance for a fixed number of wavelengths.
A Twophase Approach for Dynamic Lightpath Scheduling in WDM Optical Networks
"... Abstract — Lightpath scheduling is an important capability in nextgeneration wavelengthdivision multiplexing (WDM) optical networks to reserve resources in advance for a specified time period while provisioning endtoend lightpaths. In a dynamic environment, the end user requests for dynamic sche ..."
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Abstract — Lightpath scheduling is an important capability in nextgeneration wavelengthdivision multiplexing (WDM) optical networks to reserve resources in advance for a specified time period while provisioning endtoend lightpaths. In a dynamic environment, the end user requests for dynamic scheduled lightpath demands (DSLDs) need to be serviced without the knowledge of future requests. Even though the starting time of the request may be hours or days from the current time, the enduser however expects a quick response as to whether the request could be satisfied. We propose a twophase approach to dynamically schedule and provision DSLDs. In the first phase, termed the deterministic lightpath scheduling phase, upon arrival of a lightpath request, the network control plane schedules a path with guaranteed resources so that the user can get a quick response with a deterministic lightpath schedule. In the second phase, termed the lightpath reoptimization phase, we reprovision some already scheduled lightpaths to reoptimize for improving network performance. We study two reoptimization scenarios to reallocate network resources while maintaining the existing lightpath schedules. Experimental results show that our proposed twophase dynamic lightpath scheduling approach can greatly reduce network blocking. I.