Quazi Rahman

Dynamic Lightpath Allocation in Translucent WDM Optical Networks

The optical reach (the distance an optical signal can travel before the signal quality degrades to a level that necessitates regeneration) ranges from 500 to 2000 miles. To establish a lightpath of length greater than the optical reach, it is necessary to regenerate optical signals. In a translucent optical network, there are regeneration points, where the signal undergoes Optical-Electronic-Optical (O-E-O) conversion. In this paper we have proposed routing algorithms for translucent networks in a dynamic lightpath allocation environment in which requests for communication arrive continuously. In response to each request for communication, the objective is to establish, if possible, a path, from the source to the destination of the request for communication, so that a lightpath may be established, using the path that requires the fewest stages of regeneration. In practical transparent networks, a lightpath must satisfy the wavelength continuity constraint. However, in a translucent network, this constraint can be relaxed at the regeneration points. We have proposed an Integer Linear Program, to give the optimum results for small networks, as well as an efficient heuristic for this problem that works for larger networks. We have evaluated the heuristic through extensive simulations to establish that the heuristic produces close-to-optimal solutions in a fraction of the time needed for the optimal solutions. Our extensive evaluations demonstrate the relative impact of a set of network resources, such as (i) the number of regenerators, (ii) the optical reach of the regenerators and (iii) the number of wavelengths, on the network performance, measured in terms of the call blocking probability. To the best of our knowledge this is the first study that undertakes such an evaluation for translucent networks.

Optimal regenerator placement in translucent optical networks

The distance an optical signal can travel, before its quality degrades to a level that requires 3R-regeneration, is called the optical reach. In a translucent optical network, if an optical signal has to be communicated over a distance that exceeds the optical reach, the signal is regenerated at selected nodes of the network, so that the signal quality never degrades to an unacceptable level. Given a value of the optical reach, the goal of the Regenerator Placement Problem (RPP), in networks handling ad-hoc demands for lightpaths, is to find the minimum number of nodes capable of 3R regeneration necessary in the network and their positions, so that every pair of nodes ( u , v ) can establish a lightpath (either transparent or translucent) from u to v. In this paper we have presented two Integer Linear Program (ILP) formulations that can optimally solve the RPP problem for practical-sized networks within a reasonable amount of time. The first formulation works for networks having 35 nodes or less. The second formulation works for larger networks as well (we have reported results with up to 140 nodes). We have used a branch-and-cut approach to implement the second formulation, where we have intercepted the optimization process with control callbacks from the CPLEX callable library to introduce new constraints, as needed.

Traffic grooming in WDM mesh networks with guaranteed survivability

Traffic grooming techniques in optical networks are attracting increasing research attention in order to handle the huge bandwidth mismatch between high capacity lightpaths and low-rate individual traffic requests. It is important to have guaranteed survivability of all user connections in such networks. Path protection has emerged as a widely accepted technique for survivable WDM network design. However, it requires allocating resources for backup lightpaths, which remain idle under normal fault-free conditions. In this paper, we introduce a new design strategy for survivable traffic grooming in WDM networks, under specified resource constraints. Our approach addresses the complete design problem including logical topology design, RWA, and routing of (subwavelength) requests over the logical topology. We further ensure that the resultant logical topology is able to handle the entire traffic request after any single link failure. We first present two ILP formulations for optimally designing a survivable logical topology, and then propose a heuristic for larger networks. Experimental results demonstrate that this new approach is able to provide guaranteed bandwidth, and is much more efficient in terms of resource utilization, compared to both dedicated and shared path protection.

On static RWA in translucent optical networks

The distance an optical signal can travel before the signal quality degrades to a level that necessitates regeneration is called the optical reach. To establish a lightpath of length greater than the optical reach, it is necessary to regenerate optical signals at one or more nodes. In this paper we have proposed routing and wavelength assignment algorithms for translucent networks. For each request for a lightpath, the objective is to find a route from the source to the destination of the request, so that a translucent lightpath may be established that requires the fewest possible stages of regeneration. We have proposed an Integer Linear Programming (ILP) formulation that gives the optimum solutions for small networks. For larger networks, we have proposed an efficient heuristic. We have shown that the heuristic produces close-to-optimal solutions in a fraction of the time needed for the optimal solutions.

A Branch, Price and Cut Approach for Optimal Traffic Grooming in WDM Optical Networks

The standard approach of using multi-commodity network flow (MCNF) techniques for designing optimal WDM networks often lead to computationally difficult Mixed Integer Linear Programs (MILP) which work only on small networks. Modern Operations Research (OR) techniques may be helpful when developing efficient algorithms for large WDM networks. This paper explores the Branch, Price and Cut techniques for designing optimal WDM optical networks. We have studied a well-known problem in WDM networks - non-bifurcated traffic grooming over a specified logical topology. The standard way to solve this problem is to view it as a MCNF problem and solve the resulting MILP using a commercial MILP solver package, such as the ILOG CPLEX to give us an optimum traffic grooming strategy. The number of binary variables and the number of constraints of the MCNF problems increases with the network size and tools such as the CPLEX solver takes increasingly longer time. We have shown how we can take advantage of the structural properties of this problem and solve it efficiently using modern Operations Research techniques.

Optimal regenerator placement in survivable translucent networks

In optical networks, the optical reach is defined as the distance an optical signal can travel, before its quality degrades to a level that requires 3R-regeneration. In a translucent optical network, if an optical signal has to be communicated over a distance that exceeds the optical reach, the signal is regenerated at selected nodes of the network, so that the signal quality never degrades to an unacceptable level. Given a value of the optical reach, the goal of the Regenerator Placement Problem (RPP) in dynamic Physical Impairment aware Route and Wavelength Assignment (PI-RWA), for survivable translucent networks, is to identify the minimum number of nodes capable of 3R regeneration, so that every pair of nodes (u, v) can establish a lightpath (either transparent or translucent) from u to v. In a survivable network, even if any fault occurs, it must be guaranteed that every pair of surviving nodes (u, v) can still establish a lightpath (either transparent or translucent) from u to v, avoiding all faulty nodes/edges. In this paper we have presented a Integer Linear Program (ILP) formulation that can optimally solve the survivable RPP problem for practical-sized networks within a reasonable amount of time. We have used a branch-and-cut approach to implement our algorithm, where we have intercepted the optimization process with control callbacks from the CPLEX callable library to introduce new constraints, as needed.

Resource efficient network design and traffic grooming strategy with guaranteed survivability

Abstract In WDM networks, path protection has emerged as a widely accepted technique for providing guaranteed survivability of network traffic. However, it requires allocating resources for backup lightpaths, which remain idle under normal fault-free conditions. In this paper, we introduce a new design strategy for survivable network design, which guarantees survivability of all ongoing connections that requires significantly fewer network resources than protection based techniques. In survivable routing, the goal is to find a Route and Wavelength Assignment (RWA) such that the logical topology remains connected for all single link failures. However, even if the logical topology remains connected after any single link fault, it may not have sufficient capacity to support all the requests for data communication, for all single fault scenarios. To address this deficiency, we have proposed two independent but related problem formulations. To handle our first formulation, we have presented an Integer Linear Program (ILP) that augments the concept of survivable routing by allowing rerouting of sub-wavelength traffic carried on each lightpath and finding an RWA that maximizes the amount of traffic that can be supported by the network in the presence of any single link failure. To handle our second formulation, we have proposed a new design approach that integrates the topology design and the RWA in such a way that the resulting logical topology is able to handle the entire set of traffic requests after any single link failure. For the second problem, we have first presented an ILP formulation for optimally designing a survivable logical topology, and then proposed a heuristic for larger networks. Experimental results demonstrate that this new approach is able to provide guaranteed bandwidth, and is much more efficient in terms of resource utilization, compared to both dedicated and shared path protection schemes.

Construction of a Webportal and User Management Framework for Grid

User management is a vital problem to be solved when constructing a Webportal for accessing grid resources. Most current approaches treat web and grid users separately. This is inconvenient to the system users. This paper presents a user management framework that combines the two kinds of user management. It also supports Single Sign- On and federated identity service through integration of different technologies such as Shibboleth, MyProxy and PURSe portlets.

Logical topology design for WDM networks using tabu search

In this paper the problem of designing optimal logical topologies for WDM networks using the tabu search meta-heuristic has been considered. For a given physical topology and requests for data communication at specified rates between different pairs of nodes in the network, our objective is to obtain a logical topology, using the tabu search, to minimize the network congestion.

Optimal regenerator placement for path protection in impairment-aware WDM networks

This paper addresses the regenerator placement problem (RPP) when designing resilient, impairment aware WDM optical networks. For the RPP, we have proposed two solutions; an optimal solution for small networks (less than 10 nodes) and a near-optimal heuristic solution for practical-sized networks. The optimal solution uses an Integer Linear Program which can be implemented by any solver for mathematical programming. The heuristic makes use of an approach, proposed in a recent paper, that requires a formulation involving an exponential number of constraints. It was shown in that paper that this formulation can be solved very efficiently using a branch-and-cut algorithm and that the approach may be used to design resilient networks which guarantees restoration. In this paper we have shown that this branch-and-cut approach may be used as a part of a highly efficient heuristic which gave optimal results in an overwhelming number of cases that we tested.