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Emily Dylan

Technical University of Munich, Project Audit, Department Member

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I want to find a partner who is willing to enjoy life with me, discuss beautiful articles, do anything and go anywhere
Supervisors: Project audit director for a Fortune 500 company, investing in real estate, stocks, and and cryptocurrencies.
Address: Munich

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Professor Graeme Brooker

Royal College of Art

Quentin F Stout

University of Michigan

Kansas State University

University of Cologne

Fatiha Djemili Tolba

Badji Mokhtar - Annaba University

Monash University

University of Dhaka, Bangladesh

Journal of Computer Science IJCSIS

Vladana Putnik Prica

University of Belgrade

Vladimir Chernetsky

University of Southern California

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Papers by Emily Dylan

Primal meets dual: A generalized theory of logical topology survivability in IP-over-WDM optical networks

2010 Second International Conference on COMmunication Systems and NETworks (COMSNETS 2010), 2010

Linear time construction of redundant trees for recovery schemes enhancing QoP and QoS

Proceedings IEEE 24th Annual Joint Conference of the IEEE Computer and Communications Societies.

Medard, Finn, Barry and Gallager proposed an elegant recovery scheme (known as the MFBG scheme) u... more Medard, Finn, Barry and Gallager proposed an elegant recovery scheme (known as the MFBG scheme) using redundant trees. Xue, Chen and Thulasiraman extended the MFBG scheme and introduced the concept of quality of protection (QoP) as a metric of multifailure recovery capabilities for single failure recovery schemes. In this paper, we present three linear time algorithms for constructing redundant trees for single link failure recovery in 2-edge connected graphs and for single node failure recovery in 2-connected graphs. Our first algorithm aims at high QoP for single link recovery schemes in 2-edge connected graphs. The previous best algorithm has a running time of O(n 2 (m + n)), where n and m are the number of nodes and links in the network. Our algorithm has a running time of O(m + n), with comparable performance. Our second algorithm aims at high QoS for single link recovery schemes in 2-edge connected graphs. Our algorithm improves the previous best algorithm with O(n 2 (m + n)) time complexity to O(m + n) time complexity with comparable performance. Our third algorithm aims at high QoS for single node recovery schemes in 2-connected graphs. Again, our algorithm improves the previous best algorithm with O(n 2 (m + n)) time complexity to O(m + n) time complexity with comparable performance. Simulation results show that our new algorithms outperform previously known linear time algorithms significantly in terms of QoP or QoS, and outperform other known algorithms in terms of running time, with comparable QoP of QoS performance.

Quality-of-service and quality-of-protection issues in preplanned recovery schemes using redundant trees

IEEE Journal on Selected Areas in Communications, 2003

An improved algorithm for optimal lightpath establishment on a tree topology

IEEE Journal on Selected Areas in Communications, 2006

A Polynomial-Time Algorithm for Computing Disjoint Lightpath Pairs in Minimum Isolated-Failure-Immune WDM Optical Networks

IEEE/ACM Transactions on Networking, 2014

A fundamental problem in survivable routing in wavelength division multiplexing (WDM) optical net... more A fundamental problem in survivable routing in wavelength division multiplexing (WDM) optical networks is the computation of a pair of link-disjoint (or node-disjoint) lightpaths connecting a source with a destination, subject to the wavelength continuity constraint. However, this problem is NP-hard when the underlying network topology is a general mesh network. As a result, heuristic algorithms and integer linear programming (ILP) formulations for solving this problem have been proposed. In this paper, we advocate the use of 2-edge connected (or 2-node connected) subgraphs of minimum isolated failure immune networks as the underlying topology for WDM optical networks. We present a polynomial-time algorithm for computing a pair of link-disjoint lightpaths with shortest total length in such networks. The running time of our algorithm is , where is the number of nodes, and is the number of wavelengths per link. Numerical results are presented to demonstrate the effectiveness and scalability of our algorithm. Extension of our algorithm to the node-disjoint case is straightforward. Index Terms-Disjoint lightpath pairs, minimum isolated failure immune networks, partial 2-trees, wavelength division multiplexing (WDM) optical network.

Faster Algorithms for Construction of Recovery Trees Enhancing QoP and QoS

IEEE/ACM Transactions on Networking, 2008

Global optimization properties of parallel cooperative search algorithms: A simulation study

Parallel Computing, 2000

Cooperative search is a parallelization strategy where parallelism is obtained by concurrently ex... more Cooperative search is a parallelization strategy where parallelism is obtained by concurrently executing several search programs for the same optimization problem instance. The programs cooperate by exchanging information on previously explored regions of the solution space. When the sharing of information overlaps among several programs, changes in the search behavior of one program can propagate over time to several other programs; this is a process called diusion in physical systems. The optimization properties of diusion dynamics in cooperative algorithms have not been formally established. However, it is generally believed that when the selection of shared information is biased by the cost (objective) function, diffusion dynamics help to improve the search of cooperating programs. In this study, we simulate this aspect of cooperative algorithms using cellular automata (CAs) (these are arti®cial dynamical systems often used to simulate the dynamics of complex systems). Our results show that the sharing of information based on the cost function does not aect the diusion dynamics and therefore does not seem to help the optimization strategy of cooperating programs. However, this study increases our understanding of the role played by diusion processes in cooperative algorithms. We suggest new approaches that can help to subordinate diusion dynamics to the optimization goals of the search programs.

On the partial path protection scheme for WDM optical networks and polynomial time computability of primary and secondary paths

Journal of Industrial and Management Optimization, 2007

Logical Topology Design for IP-over-WDM Networks: A Hybrid Approach for Minimum Protection Capacity

Abstract—The problem of designing high capacity and high bit rate IP-over-WDM networks, which can... more Abstract—The problem of designing high capacity and high bit rate IP-over-WDM networks, which can provide uninterrupted service in the presence of network equipment failures, continues toattract significant interest from the research community. An IP-over-WDM network implements Internet Protocol (IP) directly over physical WDM network by establishing lightpaths using IP routers, optical crossconnects (OXC) and optical fibers. Generally an optical fiber carries several lightpaths and all of them get disconnected, if the fiber carrying them fails. Such failures can quickly impact the performance of the entire network. If IP routers can find paths to all the nodes in the network, then the network can continue to provide service without significant performance degradation. This can be achieved by reserving network resources (protection) or provisioning the network with some additional capacity (restoration). Such networks are usually called survivable networks. In this paper, we propose...

Computing the shortest network under a fixed topology

IEEE Transactions on Computers, 2002

The second improvement upon [13] is based upon the observation that an 0-sequence may be used to ... more The second improvement upon [13] is based upon the observation that an 0-sequence may be used to check the final state of a transition. This property is utilized, in the generation of checking sequences, to allow overlap between the 0-sequences and the test segments. This further contributes to a reduction in the length of the checking sequence. The method given in this paper might be further enhanced in two ways. First, the connecting transitions might be chosen from the set of transitions of the given FSM M during optimization, rather than being drawn from a cycle-free subset (E 00) found prior to optimization. This may be achieved by including a copy of each transition and relying upon properties of the optimization algorithm, which starts with the production of a minimal symmetric augmentation, that guarantee that the set chosen is cycle free. Second, prefixes of the distinguishing sequence may be used to recognize states.

Finding a Path Subject to Many Additive QoS Constraints

IEEE/ACM Transactions on Networking, 2007

A fundamental problem in Quality-of-Service (QoS) routing is to find a path between a source-dest... more A fundamental problem in Quality-of-Service (QoS) routing is to find a path between a source-destination node pair that satisfies two or more end-to-end QoS constraints. We model this problem using a graph with n vertices and m edges with K additive QoS parameters associated with each edge, for any constant K ≥ 2. This problem is known to be NP-hard. Fully polynomial time approximation schemes (FPTAS) for the case of K = 2 have been reported in the literature. We concentrate on the general case and make the following contributions. (1) We present a very simple O(Km + n log n) time K-approximation algorithm that can be used in hop-by-hop routing protocols. (2) We present an FPTAS for one optimization version of the QoS routing problem with a time complexity of O(m(n) K−1). (3) We present an FPTAS for another optimization version of the QoS routing problem with a time complexity of O(n log n + m(H) K−1) when there exists an H-hop path satisfying all QoS constraints. When K is reduced to 2, our results compare favorably with existing algorithms. The results of this paper hold for both directed and undirected graphs. For ease of presentation, undirected graph is used.

Optimum logical topology routing in an IP-over-WDM optical network and physical link failure localization: An integrated approach

2013 5th International Congress on Ultra Modern Telecommunications and Control Systems and Workshops (ICUMT), 2013

The survivable logical topology routing problem for a given IP-over-WDM network is to map each lo... more The survivable logical topology routing problem for a given IP-over-WDM network is to map each logical link into a lightpath in the physical network which guarantees connectivity of the IP network after any physical link failure. Such a survivable routing is said to protect the logical network against all single physical link failures. But, it is possible that a logical topology may not admit a survivable routing. In view of this, we define a logical topology routing to be optimum if this routing maximizes the number of single physical link failures that do not disconnect the logical topology. First, we give a mixed integer linear programming formulation to determine an optimum logical topology routing. The failure localization problem is to localize the single physical link failures which disconnect the logical network under a given optimum routing. Given a set of monitoring trails and the lightpath routings in an optimum routing, we give a mixed integer linear programming formulation to determine an optimum routing and the corresponding failure localization. We also propose a heuristic approach for these problems to handle large scale IP-over-WDM networks.

Logical topology survivability in IP-over-WDM networks: Survivable lightpath routing for maximum logical topology capacity and minimum spare capacity requirements

2011 8th International Workshop on the Design of Reliable Communication Networks (DRCN), 2011

The survivable logical topology mapping problem in an IP-over-WDM optical network is to map each ... more The survivable logical topology mapping problem in an IP-over-WDM optical network is to map each link (u, v) in the logical topology (at the IP layer) into a lightpath between the nodes u and v in the physical topology (at the optical layer) such that failure of a physical link does not cause the logical topology to become disconnected. It is assumed that both the physical and logical topologies are 2-edge connected. For this problem two lines of investigations have been pursued in the literature: one pioneered by Modiano et al., and the other pioneered by Kurant and Thiran. Since then there have been a great deal of research on this problem. Most of the works have not considered limitations imposed on the routings by physical capacity limits. In this paper, we first introduce two concepts: weakly survivable routing and strongly survivable routing. We then provide mathematical programming formulations for two problems. Problem 1 is to design a survivable lightpath routing that maximizes the logical capacity available before and after a physical link failure. The second problem is to add spare capacities to the physical links to guarantee routability of all logical link demands before and after a physical link failure. The frameworks provided by our formulation can be used to accommodate other scenarios such as those involving load balancing and fair capacity allocation constraints. We conclude with simulations that compare the results using these formulations and those obtained by heuristics that mitigate the computational complexity of the mathematical programming formulations. 2011 8th International Workshop on the Design of Reliable Communication Networks (DRCN)

Robustness of logical topology mapping algorithms for survivability against multiple failures in an IP-over-WDM optical network

2012 Fourth International Conference on Communication Systems and Networks (COMSNETS 2012), 2012

The survivable logical topology mapping (SLTM) problem in an IP-over-WDM optical network is to ma... more The survivable logical topology mapping (SLTM) problem in an IP-over-WDM optical network is to map each link (u, v) in the logical topology GL (at the IP layer) into a lightpath between the nodes u and v in the physical topology GP (at the optical layer) such that failure of a physical link does not cause the logical topology to become disconnected. It is assumed that both the physical and logical topologies are 2-edge connected. There are two lines of approach for the study of the SLTM problem. One approach uses Integer Linear Programming formulations. The main drawback with this approach is the use of exponential number of constraints, one for each cutset in GL. Moreover, it does not provide insight into the solution when survivability against multiple physical failures is required. The other approach, called the structural approach, uses graph theory and was pioneered by Kurant and Thiran and further generalized by us. In this paper we first present a generalized algorithmic framework for the SLTM problem. This framework includes several other frameworks considered in earlier works as special cases. We then define the concept of robustness of a mapping algorithm which captures the ability of the algorithm to provide survivability against multiple physical failures. This is similar to the concept of fault coverage used in hardware/software testing. We analyse the different frameworks for their robustness property. Using simulations, we demonstrate that even when an algorithm cannot be guaranteed to provide survivability against multiple failures, its robustness could be very high. The work also provides a basis for the design of survivability mapping algorithms when special classes of failures such as SRLG failures are to be protected against.

Dominator sequences in bipartite graphs

Theoretical Computer Science

Let G = (V, E) be a bipartite graph with bipartition X, Y and let |X| ≤ |Y |. A dominator sequenc... more Let G = (V, E) be a bipartite graph with bipartition X, Y and let |X| ≤ |Y |. A dominator sequence in G is a sequence of vertices (x 1 , x 2 ,. .. , x k) in X such that for each i with 2 ≤ i ≤ k, the vertex x i dominates at least one vertex in Y which is not dominated by x 1 , x 2 ,. .. , x i−1. The maximum length of a dominator sequence in G is called the dominator sequence number of G and is denoted by l(G). In this paper we present several basic results on this parameter. We prove that the decision problem for the parameter l(G) is NP-Complete. We obtain bounds for l(G) and discuss applications in the study of optical networks.

Multilevel cooperative search problem: application to the circuit/hypergraph partitioning

In this paper, we present an adaptation for hypergraph partitioning of the multilevel cooperative... more In this paper, we present an adaptation for hypergraph partitioning of the multilevel cooperative search paradigm first introduce by Toulouse, Thulasiraman, and Glover [15]. We also introduce a new approach for coarsening hypergraphs, and describe a parallel implementation of this algorithm on the SGI O200 system. Experiments on ISPD98 benchmark suite of circuits show, for 4-way and 8-way partitioning, a reduction of 3% to 15% on hyperedge-cut compared to hMETIS. Bisections of hypergraphs based on our algorithm also outperforms hMETIS, although more modestly.

Multilevel Cooperative Search: Application to the Circuit/Hypergraph Partitioning Problem

Proceedings of the …, 2000

In this paper, we present an adaptation for hypergraph par-titioning of the multilevel cooperativ... more

Self-organization in cooperative tabu search algorithms

The search history of memory based heuristics like tabu search can be used to design a category o... more

Realization of modified cut-set matrix and applications

IEEE Transactions on Circuit Theory, 1970

The concepts of network of departure and padding n-port network are defined and certain important... more The concepts of network of departure and padding n-port network are defined and certain important properties of these is the diagonal matrix of edge conductances of N, then networks are stated. A necessary and sufficient criterion for the the cut-set admittance matrix Y, of N is given by realization of the modified cut-set matrix of a resistive n-port network having a prescribed configuration is given. A new approach (1) to the synthesis of short-circuit conductance matrix of a resistive n-port network with more than (n + 1) nodes is outlined. Necessary and sufficient conditions for the realization of the potential factor in which the rows and columns of Y,, correspond to the matrix of an (n + 2) node resistive n-port network are also obtained. port edges and those of Y,, correspond to the nonport _ These conditions lead to a simple t&t for the realizability of the edges. modified cut-set matrix of an (n + 2) node n-port network. Examples

Multi-level cooperative search: A new paradigm for combinatorial optimization and an application to graph partitioning

by Fred Glover, Michel Toulouse, and Emily Dylan

. Cooperative search is a parallelization strategy for searchalgorithms where parallelism is obta... more . Cooperative search is a parallelization strategy for searchalgorithms where parallelism is obtained by concurrently executing severalsearch programs. The solution space is implicitly decomposed accordingto the search strategy of each program. The programs cooperateby exchanging information on previously explored regions of the solutionspace. In this paper we propose a new design for cooperative searchalgorithms which is also a new parallel

Primal meets dual: A generalized theory of logical topology survivability in IP-over-WDM optical networks

2010 Second International Conference on COMmunication Systems and NETworks (COMSNETS 2010), 2010

Linear time construction of redundant trees for recovery schemes enhancing QoP and QoS

Proceedings IEEE 24th Annual Joint Conference of the IEEE Computer and Communications Societies.

Medard, Finn, Barry and Gallager proposed an elegant recovery scheme (known as the MFBG scheme) u... more Medard, Finn, Barry and Gallager proposed an elegant recovery scheme (known as the MFBG scheme) using redundant trees. Xue, Chen and Thulasiraman extended the MFBG scheme and introduced the concept of quality of protection (QoP) as a metric of multifailure recovery capabilities for single failure recovery schemes. In this paper, we present three linear time algorithms for constructing redundant trees for single link failure recovery in 2-edge connected graphs and for single node failure recovery in 2-connected graphs. Our first algorithm aims at high QoP for single link recovery schemes in 2-edge connected graphs. The previous best algorithm has a running time of O(n 2 (m + n)), where n and m are the number of nodes and links in the network. Our algorithm has a running time of O(m + n), with comparable performance. Our second algorithm aims at high QoS for single link recovery schemes in 2-edge connected graphs. Our algorithm improves the previous best algorithm with O(n 2 (m + n)) time complexity to O(m + n) time complexity with comparable performance. Our third algorithm aims at high QoS for single node recovery schemes in 2-connected graphs. Again, our algorithm improves the previous best algorithm with O(n 2 (m + n)) time complexity to O(m + n) time complexity with comparable performance. Simulation results show that our new algorithms outperform previously known linear time algorithms significantly in terms of QoP or QoS, and outperform other known algorithms in terms of running time, with comparable QoP of QoS performance.

Quality-of-service and quality-of-protection issues in preplanned recovery schemes using redundant trees

IEEE Journal on Selected Areas in Communications, 2003

An improved algorithm for optimal lightpath establishment on a tree topology

IEEE Journal on Selected Areas in Communications, 2006

A Polynomial-Time Algorithm for Computing Disjoint Lightpath Pairs in Minimum Isolated-Failure-Immune WDM Optical Networks

IEEE/ACM Transactions on Networking, 2014

A fundamental problem in survivable routing in wavelength division multiplexing (WDM) optical net... more A fundamental problem in survivable routing in wavelength division multiplexing (WDM) optical networks is the computation of a pair of link-disjoint (or node-disjoint) lightpaths connecting a source with a destination, subject to the wavelength continuity constraint. However, this problem is NP-hard when the underlying network topology is a general mesh network. As a result, heuristic algorithms and integer linear programming (ILP) formulations for solving this problem have been proposed. In this paper, we advocate the use of 2-edge connected (or 2-node connected) subgraphs of minimum isolated failure immune networks as the underlying topology for WDM optical networks. We present a polynomial-time algorithm for computing a pair of link-disjoint lightpaths with shortest total length in such networks. The running time of our algorithm is , where is the number of nodes, and is the number of wavelengths per link. Numerical results are presented to demonstrate the effectiveness and scalability of our algorithm. Extension of our algorithm to the node-disjoint case is straightforward. Index Terms-Disjoint lightpath pairs, minimum isolated failure immune networks, partial 2-trees, wavelength division multiplexing (WDM) optical network.

Faster Algorithms for Construction of Recovery Trees Enhancing QoP and QoS

IEEE/ACM Transactions on Networking, 2008

Global optimization properties of parallel cooperative search algorithms: A simulation study

Parallel Computing, 2000

Cooperative search is a parallelization strategy where parallelism is obtained by concurrently ex... more Cooperative search is a parallelization strategy where parallelism is obtained by concurrently executing several search programs for the same optimization problem instance. The programs cooperate by exchanging information on previously explored regions of the solution space. When the sharing of information overlaps among several programs, changes in the search behavior of one program can propagate over time to several other programs; this is a process called diusion in physical systems. The optimization properties of diusion dynamics in cooperative algorithms have not been formally established. However, it is generally believed that when the selection of shared information is biased by the cost (objective) function, diffusion dynamics help to improve the search of cooperating programs. In this study, we simulate this aspect of cooperative algorithms using cellular automata (CAs) (these are arti®cial dynamical systems often used to simulate the dynamics of complex systems). Our results show that the sharing of information based on the cost function does not aect the diusion dynamics and therefore does not seem to help the optimization strategy of cooperating programs. However, this study increases our understanding of the role played by diusion processes in cooperative algorithms. We suggest new approaches that can help to subordinate diusion dynamics to the optimization goals of the search programs.

On the partial path protection scheme for WDM optical networks and polynomial time computability of primary and secondary paths

Journal of Industrial and Management Optimization, 2007

Logical Topology Design for IP-over-WDM Networks: A Hybrid Approach for Minimum Protection Capacity

Abstract—The problem of designing high capacity and high bit rate IP-over-WDM networks, which can... more Abstract—The problem of designing high capacity and high bit rate IP-over-WDM networks, which can provide uninterrupted service in the presence of network equipment failures, continues toattract significant interest from the research community. An IP-over-WDM network implements Internet Protocol (IP) directly over physical WDM network by establishing lightpaths using IP routers, optical crossconnects (OXC) and optical fibers. Generally an optical fiber carries several lightpaths and all of them get disconnected, if the fiber carrying them fails. Such failures can quickly impact the performance of the entire network. If IP routers can find paths to all the nodes in the network, then the network can continue to provide service without significant performance degradation. This can be achieved by reserving network resources (protection) or provisioning the network with some additional capacity (restoration). Such networks are usually called survivable networks. In this paper, we propose...

Computing the shortest network under a fixed topology

IEEE Transactions on Computers, 2002

The second improvement upon [13] is based upon the observation that an 0-sequence may be used to ... more The second improvement upon [13] is based upon the observation that an 0-sequence may be used to check the final state of a transition. This property is utilized, in the generation of checking sequences, to allow overlap between the 0-sequences and the test segments. This further contributes to a reduction in the length of the checking sequence. The method given in this paper might be further enhanced in two ways. First, the connecting transitions might be chosen from the set of transitions of the given FSM M during optimization, rather than being drawn from a cycle-free subset (E 00) found prior to optimization. This may be achieved by including a copy of each transition and relying upon properties of the optimization algorithm, which starts with the production of a minimal symmetric augmentation, that guarantee that the set chosen is cycle free. Second, prefixes of the distinguishing sequence may be used to recognize states.

Finding a Path Subject to Many Additive QoS Constraints

IEEE/ACM Transactions on Networking, 2007

A fundamental problem in Quality-of-Service (QoS) routing is to find a path between a source-dest... more A fundamental problem in Quality-of-Service (QoS) routing is to find a path between a source-destination node pair that satisfies two or more end-to-end QoS constraints. We model this problem using a graph with n vertices and m edges with K additive QoS parameters associated with each edge, for any constant K ≥ 2. This problem is known to be NP-hard. Fully polynomial time approximation schemes (FPTAS) for the case of K = 2 have been reported in the literature. We concentrate on the general case and make the following contributions. (1) We present a very simple O(Km + n log n) time K-approximation algorithm that can be used in hop-by-hop routing protocols. (2) We present an FPTAS for one optimization version of the QoS routing problem with a time complexity of O(m(n) K−1). (3) We present an FPTAS for another optimization version of the QoS routing problem with a time complexity of O(n log n + m(H) K−1) when there exists an H-hop path satisfying all QoS constraints. When K is reduced to 2, our results compare favorably with existing algorithms. The results of this paper hold for both directed and undirected graphs. For ease of presentation, undirected graph is used.

Optimum logical topology routing in an IP-over-WDM optical network and physical link failure localization: An integrated approach

2013 5th International Congress on Ultra Modern Telecommunications and Control Systems and Workshops (ICUMT), 2013

The survivable logical topology routing problem for a given IP-over-WDM network is to map each lo... more The survivable logical topology routing problem for a given IP-over-WDM network is to map each logical link into a lightpath in the physical network which guarantees connectivity of the IP network after any physical link failure. Such a survivable routing is said to protect the logical network against all single physical link failures. But, it is possible that a logical topology may not admit a survivable routing. In view of this, we define a logical topology routing to be optimum if this routing maximizes the number of single physical link failures that do not disconnect the logical topology. First, we give a mixed integer linear programming formulation to determine an optimum logical topology routing. The failure localization problem is to localize the single physical link failures which disconnect the logical network under a given optimum routing. Given a set of monitoring trails and the lightpath routings in an optimum routing, we give a mixed integer linear programming formulation to determine an optimum routing and the corresponding failure localization. We also propose a heuristic approach for these problems to handle large scale IP-over-WDM networks.

Logical topology survivability in IP-over-WDM networks: Survivable lightpath routing for maximum logical topology capacity and minimum spare capacity requirements

2011 8th International Workshop on the Design of Reliable Communication Networks (DRCN), 2011

The survivable logical topology mapping problem in an IP-over-WDM optical network is to map each ... more The survivable logical topology mapping problem in an IP-over-WDM optical network is to map each link (u, v) in the logical topology (at the IP layer) into a lightpath between the nodes u and v in the physical topology (at the optical layer) such that failure of a physical link does not cause the logical topology to become disconnected. It is assumed that both the physical and logical topologies are 2-edge connected. For this problem two lines of investigations have been pursued in the literature: one pioneered by Modiano et al., and the other pioneered by Kurant and Thiran. Since then there have been a great deal of research on this problem. Most of the works have not considered limitations imposed on the routings by physical capacity limits. In this paper, we first introduce two concepts: weakly survivable routing and strongly survivable routing. We then provide mathematical programming formulations for two problems. Problem 1 is to design a survivable lightpath routing that maximizes the logical capacity available before and after a physical link failure. The second problem is to add spare capacities to the physical links to guarantee routability of all logical link demands before and after a physical link failure. The frameworks provided by our formulation can be used to accommodate other scenarios such as those involving load balancing and fair capacity allocation constraints. We conclude with simulations that compare the results using these formulations and those obtained by heuristics that mitigate the computational complexity of the mathematical programming formulations. 2011 8th International Workshop on the Design of Reliable Communication Networks (DRCN)

Robustness of logical topology mapping algorithms for survivability against multiple failures in an IP-over-WDM optical network

2012 Fourth International Conference on Communication Systems and Networks (COMSNETS 2012), 2012

The survivable logical topology mapping (SLTM) problem in an IP-over-WDM optical network is to ma... more The survivable logical topology mapping (SLTM) problem in an IP-over-WDM optical network is to map each link (u, v) in the logical topology GL (at the IP layer) into a lightpath between the nodes u and v in the physical topology GP (at the optical layer) such that failure of a physical link does not cause the logical topology to become disconnected. It is assumed that both the physical and logical topologies are 2-edge connected. There are two lines of approach for the study of the SLTM problem. One approach uses Integer Linear Programming formulations. The main drawback with this approach is the use of exponential number of constraints, one for each cutset in GL. Moreover, it does not provide insight into the solution when survivability against multiple physical failures is required. The other approach, called the structural approach, uses graph theory and was pioneered by Kurant and Thiran and further generalized by us. In this paper we first present a generalized algorithmic framework for the SLTM problem. This framework includes several other frameworks considered in earlier works as special cases. We then define the concept of robustness of a mapping algorithm which captures the ability of the algorithm to provide survivability against multiple physical failures. This is similar to the concept of fault coverage used in hardware/software testing. We analyse the different frameworks for their robustness property. Using simulations, we demonstrate that even when an algorithm cannot be guaranteed to provide survivability against multiple failures, its robustness could be very high. The work also provides a basis for the design of survivability mapping algorithms when special classes of failures such as SRLG failures are to be protected against.

Dominator sequences in bipartite graphs

Theoretical Computer Science

Let G = (V, E) be a bipartite graph with bipartition X, Y and let |X| ≤ |Y |. A dominator sequenc... more Let G = (V, E) be a bipartite graph with bipartition X, Y and let |X| ≤ |Y |. A dominator sequence in G is a sequence of vertices (x 1 , x 2 ,. .. , x k) in X such that for each i with 2 ≤ i ≤ k, the vertex x i dominates at least one vertex in Y which is not dominated by x 1 , x 2 ,. .. , x i−1. The maximum length of a dominator sequence in G is called the dominator sequence number of G and is denoted by l(G). In this paper we present several basic results on this parameter. We prove that the decision problem for the parameter l(G) is NP-Complete. We obtain bounds for l(G) and discuss applications in the study of optical networks.

Multilevel cooperative search problem: application to the circuit/hypergraph partitioning

In this paper, we present an adaptation for hypergraph partitioning of the multilevel cooperative... more In this paper, we present an adaptation for hypergraph partitioning of the multilevel cooperative search paradigm first introduce by Toulouse, Thulasiraman, and Glover [15]. We also introduce a new approach for coarsening hypergraphs, and describe a parallel implementation of this algorithm on the SGI O200 system. Experiments on ISPD98 benchmark suite of circuits show, for 4-way and 8-way partitioning, a reduction of 3% to 15% on hyperedge-cut compared to hMETIS. Bisections of hypergraphs based on our algorithm also outperforms hMETIS, although more modestly.

Multilevel Cooperative Search: Application to the Circuit/Hypergraph Partitioning Problem

Proceedings of the …, 2000

In this paper, we present an adaptation for hypergraph par-titioning of the multilevel cooperativ... more

Self-organization in cooperative tabu search algorithms

The search history of memory based heuristics like tabu search can be used to design a category o... more

Realization of modified cut-set matrix and applications

IEEE Transactions on Circuit Theory, 1970

The concepts of network of departure and padding n-port network are defined and certain important... more The concepts of network of departure and padding n-port network are defined and certain important properties of these is the diagonal matrix of edge conductances of N, then networks are stated. A necessary and sufficient criterion for the the cut-set admittance matrix Y, of N is given by realization of the modified cut-set matrix of a resistive n-port network having a prescribed configuration is given. A new approach (1) to the synthesis of short-circuit conductance matrix of a resistive n-port network with more than (n + 1) nodes is outlined. Necessary and sufficient conditions for the realization of the potential factor in which the rows and columns of Y,, correspond to the matrix of an (n + 2) node resistive n-port network are also obtained. port edges and those of Y,, correspond to the nonport _ These conditions lead to a simple t&t for the realizability of the edges. modified cut-set matrix of an (n + 2) node n-port network. Examples

Multi-level cooperative search: A new paradigm for combinatorial optimization and an application to graph partitioning

by Fred Glover, Michel Toulouse, and Emily Dylan

. Cooperative search is a parallelization strategy for searchalgorithms where parallelism is obta... more . Cooperative search is a parallelization strategy for searchalgorithms where parallelism is obtained by concurrently executing severalsearch programs. The solution space is implicitly decomposed accordingto the search strategy of each program. The programs cooperateby exchanging information on previously explored regions of the solutionspace. In this paper we propose a new design for cooperative searchalgorithms which is also a new parallel