Resource efficient network design and traffic grooming strategy with guaranteed survivability

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.     

Physical topology design for survivable routing of logical rings in WDM-based networks

In a wavelength-division multiplexed (WDM)-based network, a single physical link failure may correspond to multiple logical link failures. As a result, two-connected logical topologies, such as rings routed on a WDM physical topology, may become disconnected after a single physical link failure. We consider the design of physical topologies that ensure logical rings can be embedded in a survivable manner. This is of particular interest in metropolitan area networks, where logical rings are in practice almost exclusively employed for providing protection against link failures. First, we develop necessary conditions for the physical topology to be able to embed all logical rings in a survivable manner. We then use these conditions to provide tight bounds on the number of physical links that an N-node physical topology must have in order to support all logical rings for different sizes K. We show that when K/spl ges/4 the physical topology must have at least 4N/3 links, and that when K/spl ges/6 the physical topology must have at least 3N/2 links. Subsequently, we generalize this bound for all K/spl ges/4. When K/spl ges/N-2, we show that the physical topology must have at least 2N-4 links. Finally, we design physical topologies that meet the above bounds for both K=4 and K=N-2. Specifically, our physical topology for embedding (N-2)-node rings has a dual hub structure and is able to embed all rings of size less than N-1 in a survivable manner. We also provide a simple extension to this topology that addresses rings of size K=N-1 and rings of size K=N for N odd. We observe that designing the physical topology for supporting all logical rings in a survivable manner does not use significantly more physical links than a design that only supports a small number of logical rings. Hence, our approach of designing physical topologies that can be used to embed all possible ring logical topologies does not lead to a significant overdesign of the physical topology.     

Efficient routing and wavelength assignment for reconfigurable WDMnetworks

Through the use of configurable wavelength-division-multiplexing (WDM) technology including tunable optical transceivers and frequency selective switches, next-generation WDM networks will allow multiple virtual topologies to be dynamically established on a given physical topology. For N node P port networks, we determine the number of wavelengths required to support all possible virtual topologies (PN lightpaths) on a bidirectional ring physical topology. We show that if shortest path routing is used, approximately N wavelengths are needed to map N lightpaths. We then present novel adaptive lightpath routing and wavelength assignment strategies that reduce the wavelength requirements to [(N/2)] working wavelengths per port for protected networks and [(N/3)] wavelengths in each direction per port for unprotected networks. We show that this reduced wavelength requirement is optimal in the sense that it is the minimum required to support the worst case logical topology. Furthermore, we prove that a significant number of logical topologies require this minimum number of wavelengths. We also develop joint routing and wavelength assignment strategies that not only minimize the number of wavelengths required to implement the worst case logical topologies but also reduce average wavelength requirements. Finally, methods for extending these routing and wavelength assignment results to general two-connected and three-connected physical topologies are presented     

Design of logical topologies: a linear formulation forwavelength-routed optical networks with no wavelength changers

We consider the problem of constructing logical topologies over a wavelength-routed optical network with no wavelength changers. We present a general linear formulation which considers routing traffic demands, and routing and assigning wavelengths to lightpaths, as a combined optimization problem. The formulation also takes into account the maximum number of hops a lightpath is permitted to take, multiple logical links in the logical topology, multiple physical links in the physical topology, and symmetry/asymmetry restrictions in designing logical topologies. The objective is to minimize congestion. We show by examples how equality and inequality logical degree constraints have a bearing on congestion. We prove that, under certain conditions, having equality degree constraints with multiple edges allowed in the design of logical topologies does not affect congestion. This helps in reducing the dimensionality of the search space and hence speeds up the search for an optimal solution of the linear formulation. We solve the linear formulation for small examples and show the tradeoff between congestion, number of wavelengths available and the maximum number of hops a lightpath is allowed to take. For large networks, we solve the linear formulation by relaxing the integer constraints. We develop topology design algorithms for large networks based on rounding the solutions obtained by solving the relaxed problem. Since the whole problem is linearizable, the solution obtained by relaxation of the integer constraints yields a lower bound on congestion. This is useful in comparing the efficiency of our heuristic algorithms. Following Bienstock and Gunluk (1995), we introduce a cutting plane which helps in obtaining better lower bounds on congestion and also enables us to reduce the previously obtained upper bounds on congestion     

Survivable routing in IP-over-WDM networks: An efficient and scalable local search algorithm

In IP-over-WDM networks, a logical IP network is routed on top of a physical optical fiber network. An important challenge here is to make the routing survivable. We call a routing survivable if the connectivity of the logical network is guaranteed in the case of a failure in the physical network. In this paper we describe FastSurv, a local search algorithm for survivable routing. The algorithm works in an iterative manner: after each iteration it learns more about the structure of the logical graph and in the next iteration it uses this information to improve its solution. The algorithm can take link capacity constraints into account and can be extended to deal with multiple simultaneous link failures and node failures. In a large series of tests we compare FastSurv with current state-of-the-art algorithms for this problem. We show that it can provide better solutions in much shorter time, and that it is more scalable with respect to the number of nodes, both in terms of solution quality and run time.     

Dynamic survivable mapping through reconfiguration in IP over WDM network

A new approach for network survivability problem in Intemet protocol （IP） over wavelength division multiplexing （WDM） optical network is proposed to enhance the IP layer restorability under physical link failure through logical topology reconfiguration. More specifically, after traffic arrival and departure, reconfiguring the logical topology correspondingly is helpful to minimize the traffic disruption after physical link failure. So, in this paper, this problem is proposed for first time and formulated as an integer linear programming （ILP） problem. And then, two heuristic algorithms are proposed. The performance of proposed algorithms have been evaluated through simulations, and the results show that reconfiguring the logical topology dynamically could achieve more than 20% improvement of the restorability of traffic in IP layer, but with acceptable resource cost.     

Design of Translucent Optical Networks: Partitioning and Restoration

We discuss the problem of designing translucent optical networks composed of restorable, transparent subnetworks interconnected via transponders. We develop an integer linear programming (ILP) formulation for partitioning an optical network topology into subnetworks, where the subnetworks are determined subject to the constraints that each subnetwork satisfies size limitations, and it is two-connected. A greedy heuristic partitioning algorithm is proposed for planar network topologies. We use section restoration for translucent networks where failed connections are rerouted within the subnetwork which contains the failed link. The network design problem of determining working and restoration capacities with section restoration is formulated as an ILP problem. Numerical results show that fiber costs with section restoration are close to those with path restoration for mesh topologies used in this study. It is also shown that the number of transponders with the translucent network architecture is substantially reduced compared to opaque networks.     

Generalized Survivable Network

Two important requirements for future backbone networks are full survivability against link failures and dynamic bandwidth provisioning. We demonstrate how these two requirements can be met by introducing a new survivable network concept called the generalized survivable network (GSN), which has the special property that it remains survivable no matter how traffic is provisioned dynamically, as long as the input and output constraints at the nodes are fixed. A rigorous mathematical framework for designing the GSN is presented. In particular, we focus on the GSN capacity planning problem, which finds the edge capacities for a given physical network topology with the input/output constraints at the nodes. We employ fixed single-path routing which leads to wide-sense nonblocking GSNs. We show how the initial, infeasible formal mixed integer linear programming formulation can be transformed into a more feasible problem using the duality transformation. A procedure for finding the realizable lower bound for the cost is also presented. A two-phase approach is proposed for solving the GSNCPP. We have carried out numerical computations for ten networks with different topologies and found that the cost of a GSN is only a fraction (from 39% to 97%) more than the average cost of a static survivable network. The framework is applicable to survivable network planning for ASTN/ASON, VPN, and IP networks as well as bandwidth-on-demand resource allocation.     

Selective survivability with disjoint nodes and disjoint lightpaths for layer 1 VPN

This paper deals with the problem of survivable routing and wavelength assignment in layer 1 virtual private networks (VPNs). The main idea is routing the selected lightpaths by the layer 1 VPN customer, in a link-disjoint manner. The customer may freely identify some sites or some connections, and have their related lightpaths routed through link-disjoint paths through the provider’s network. This selective survivability idea creates a new perspective for survivable routing, by giving the customer the flexibility of selecting important elements (nodes or connections) in its network. This study is different from previous studies which aim to solve the survivable routing problem for the whole VPN topology. The proposed scheme is two-fold: disjoint node based, and disjoint lightpath based. In disjoint node scheme, all lightpaths incident to a node are routed mutually through link-disjoint paths. In disjoint lightpath scheme, a lightpath is routed in a link-disjoint manner from all other ligthpaths of the VPN. We present a simple heuristic algorithm for selective survivability routing. We study the performance of this algorithm in terms of resources allocated by the selective survivability routing scheme compared to shortest path routing with no survivability. The numerical examples show that the amount of used resources by the selective survivability scheme is only slightly more than the amount used in shortest path routing, and this increase is linear. The extra resources used by the new scheme are justified by better survivability of the VPN topology in case of physical link failures, and the simplicity of the implementation.     

Survivable virtual topology mapping in IP-over-WDM networks using differential evolution optimization

In IP-over-wavelength division multiplexing networks, a virtual topology is placed over the physical topology of the optical network. Given that a simple link failure or a node failure on the physical topology can cause a significant loss of information, an important challenge is to make the routing of the virtual topology on to the physical topology survivable. This problem is known as survivable virtual topology mapping (SVTM) and is known to be an NP-complete problem. So far, this problem has been optimally solved for small instances by the application of integer linear programming and has been sub-optimally solved for more realistic instances by heuristic strategies such as ant colony optimization and genetic algorithms. In this paper, we introduce the application of differential evolution (DE) to solve the SVTM problem and enhancements based on DE are proposed as well. Three algorithms based on DE are developed. The enhanced variants have better convergence rate, get better quality of solutions and require few control parameters. We present the impact of these parameters on the system’s performance improvement. Algorithms are evaluated in different test bench optical networks, as NSFnet and USA, demonstrating that the enhanced DE algorithm overcomes the other two, for small instances. The three algorithms reach a 100  survivable mapping for small instances. The three algorithms also find positive survivable mappings and reduce the network wavelength links. Results show the effectiveness and efficiency of the proposed algorithms.     

Design of logical topologies for wavelength-routed optical networks

The problem of designing a logical topology over a wavelength-routed all-optical network (AON) physical topology is studied. The physical topology consists of the nodes and fiber links in the network. On an AON physical topology, we can set up lightpaths between pairs of nodes, where a lightpath represents a direct optical connection without any intermediate electronics. The set of lightpaths along with the nodes constitutes the logical topology. For a given network physical topology and traffic pattern, our objective is to design the logical topology and the routing algorithm so as to minimize the network congestion while constraining the average delay seen by a source-destination pair and the amount of processing required at the nodes (degree of the logical topology). Ignoring the delay constraints can result in fairly convoluted logical topologies with very long delays. On the other hand, in all our examples, imposing it results in a minimal increase in congestion. While the number of wavelengths required to imbed the resulting logical topology on the physical all optical topology is also a constraint in general, we find that in many cases of interest this number can be quite small. We formulate the combined logical topology design and routing problem described above as a mixed integer linear programming problem which we then solve for a number of cases of a six-node network. This programming problem is split into two subproblems: logical topology design, and routing. We then compare the performance of several heuristic topology design algorithms against that of randomly generated topologies, as well as lower bounds     

Path diversification for future internet end-to-end resilience and survivability

Path Diversification is a new mechanism that can be used to select multiple paths between a given ingress and egress node pair using a quantified diversity measure to achieve maximum flow reliability. The path diversification mechanism is targeted at the end-to-end layer, but can be applied at any level for which a path discovery service is available. Path diversification also takes into account service requirements for low-latency or maximal reliability in selecting appropriate paths. Using this mechanism will allow future internetworking architectures to exploit naturally rich physical topologies to a far greater extent than is possible with shortest-path routing or equal-cost load balancing. We describe the path diversity metric and its application at various aggregation levels, and apply the path diversification process to 13 real-world network graphs as well as 4 synthetic topologies to asses the gain in flow reliability. Based on the analysis of flow reliability across a range of networks, we then extend our path diversity metric to create a composite compensated total graph diversity metric that is representative of a particular topology’s survivability with respect to distributed simultaneous link and node failures. We tune the accuracy of this metric having simulated the performance of each topology under a range of failure severities, and present the results. The topologies used are from national-scale backbone networks with a variety of characteristics, which we characterize using standard graph-theoretic metrics. The end result is a compensated total graph diversity metric that accurately predicts the survivability of a given network topology.     

A Study of Path Protection in Large-Scale Optical Networks

We consider the problem of designing a network of optical cross-connects (OXCs) which provides end-to-end lightpath services to large numbers of client nodes, under the requirement that the network will survive any single-link failure. Our main objective is to quantify the additional resource requirements of implementing path protection schemes over a network with no survivability properties. To this end, we present heuristic routing and wavelength assignment algorithms for dedicated path protection and two variants of shared path protection, and integrate them into the physical and logical topology design framework we developed in an earlier study. We apply our heuristics to networks with up to 1000 client nodes, with a number of lightpaths that is an order of magnitude greater than the number of clients, and for a wide range of values for system parameters such as the number of wavelengths per fiber, the number of optical transceivers per client node, and the number of ports per OXC. Our results provide insight into the relative resource requirements of dedicated and shared path protection schemes. We also find that, using shared path protection schemes, it is possible to build cost-effective survivable networks that provide rich connectivity among client nodes with only a modest additional amount of resources over a network with no survivability properties.     

Capacity dimensioning and routing for hybrid satellite and terrestrial systems

Satellite network architecture plays an important role in the success of a satellite business. For future commercial broadband data satellite networks integrated with the terrestrial network, satellite network topology, link capacity, and routing have major impacts on the cost of the network and the amount of revenue the network can generate. To find the most cost-effective satellite network topology, we propose a unified mathematical framework using a two-stage stochastic programming formulation. The solution to the stochastic programming formulation gives optimal link capacities and an optimal routing strategy for different network topologies, taking into account uncertainties in long-term aggregate traffic statistic estimation. Using a simple satellite network example, we show the feasible topology regions for three different satellite topologies and show that, for some parameter values, the hybrid topology is more cost effective than nonhybrid topologies. In the limit of high traffic rejection cost, stochastic dimensioning reduces to static dimensioning. We study worst case static dimensioning for a general geosynchronous earth orbit satellite network and show the feasible topology regions, as well as effective cost comparisons for different topologies. We conclude with a discussion on network cost and architectural flexibility relating to satellite network design.     

An analysis of oblivious and adaptive routing in optical networkswith wavelength translation

We present an analysis for both oblivious and adaptive routing in regular, all-optical networks with wavelength translation. Our approach is simple, computationally inexpensive, accurate for both low and high network loads, and the first to analyze adaptive routing with wavelength translation in wavelength division multiplexed (WDM) networks while also providing a simpler formulation of oblivious routing with wavelength translation. Unlike some previous analyses which use the link independence blocking assumption and the call dropping (loss) model (where blocked calls are cleared), we account for the dependence between the acquisition of wavelengths on successive links of a session's path and use a lossless model (where blocked calls are retried at a later time). We show that the throughput per wavelength increases superlinearly (as expected) as we increase the number of wavelengths per link, due both to additional capacity and more efficient use of this capacity; however, the extent of this superlinear increase in throughput saturates rather quickly to a linear increase. We also examine the effect that adaptive routing can have on performance. The analytical methodology that we develop can be applied to any vertex and edge symmetric topology, and with modifications, to any vertex symmetric (but not necessarily edge symmetric) topology. We find that, for the topologies we examine, providing at most one alternate link at every hop gives a per wavelength throughput that is close to that achieved by oblivious routing with twice the number of wavelengths per link. This suggests some interesting possibilities for network provisioning in an all-optical network. We verify the accuracy of our analysis for both oblivious and adaptive routing via simulations for the torus and hypercube networks     

Shared risk link group failure restoration with in-band approximate failure localization

This paper proposes a novel failure recovery framework for multi-link shared risk link group (SRLG) failures in optical mesh networks, called failure presumed protection (FPP). The proposed framework is characterized by a failure dependent protection (FDP) mechanism where the optical layer in-band failure identification and restoration tasks for route selection are jointly considered. FPP employs in-band monitoring at each node to obtain on-off status of any working lightpath in case the lightpath is terminated at (or traversing through) the node. Since the locally available failure status at a node may not be sufficient for unambiguous failure localization, the proposed framework reroutes the interrupted lightpaths in such a way that all the suspicious links which do not have 100% restorability under any SRLG failure are kept away. We claim that this is the first study on FDP that considers both failure localization and FDP survivable routing. Extensive simulations are conducted to examine the proposed FPP method under various survivable routing architectures and implementations. The results are further compared with a large number of previously reported counterparts. We will show that the FPP framework can overcome the topological limitation which is critical to the conventional failure independent protection method (e.g., shared path protection). In addition, it can be served as a viable solution for FDP survivable routing where failure localization is considered.     

Capacity Optimization for Surviving Double-Link Failures in Mesh-Restorable Optical Networks

Most research to date in survivable optical network design and operation, focused on the failure of a single component such as a link or a node. A double-link failure model in which any two links in the network may fail in an arbitrary order was proposed recently in literature [1]. Three loop-back methods of recovering from double-link failures were also presented. The basic idea behind these methods is to pre-compute two backup paths for each link on the primary paths and reserve resources on these paths. Compared to protection methods for single-link failure model, the protection methods for double-link failure model require much more spare capacity. Reserving dedicated resources on every backup path at the time of establishing primary path itself would consume excessive resources. Moreover, it may not be possible to allocate dedicated resources on each of two backup paths around each link, due to the wavelength continuous constraint. In M. Sridharan et al., [2,3] we captured the various operational phases in survivable WDM networks as a single integer programming based (ILP) optimization problem. In this work, we extend our optimization framework to include double-link failures. We use the double-link failure recovery methods available in literature, employ backup multiplexing schemes to optimize capacity utilization, and provide 100% protection guarantee for double-link failure recovery. We develop rules to identify scenarios when capacity sharing among interacting demand sets is possible. Our results indicate that for the double-link failure recovery methods, the shared-link protection scheme provides 10–15% savings in capacity utilization over the dedicated link protection scheme which reserves dedicated capacity on two backup paths for each link. We provide a way of adapting the heuristic based double-link failure recovery methods into a mathematical framework, and use techniques to improve wavelength utilization for optimal capacity usage.     

Autonomous Reconfiguration in Free-Space Optical Sensor Networks

This research focuses on the physical and logical control and reconfigurability of network topologies through intelligent and dynamic rearrangement of nodes in an optical wireless sensor network. We address high data rate sensor networks (e.g., infrastructure monitoring; surveillance), which consist of gigabit per second, narrow beam, free-space optical links between fixed and/or mobile nodes. In our approach, the seamless operation of such networks requires maintenance of wireless link connectivity and quality and at all times, amidst, for example, changing atmospheric, and traffic and platform conditions. This is achieved by dynamic reconfiguration through topology control. We address the problem of dynamic formulation of topologies, which contain only two transceivers per communications node or switch. The task of reconfiguration requires the formation of a biconnected graph or a ring topology. The problem is similar to the traveling salesman problem and is NP complete. We address the mixed integer programming formulation of this problem, and show that it does not scale even for a small network. We then focus on heuristics for dynamic, autonomous reconfiguration. Using simulations, we investigate tradeoff between solution quality and computational time. We also investigate the effectiveness of these dynamic reconfiguration heuristics compared to fixed, degraded topologies.     

Analysis and design of resilient multifiber wavelength-routedoptical transport networks

Wavelength-routed optical networks (WRONs) are attracting significant attention for future high-capacity transport applications. This paper studies resilient multifiber WRONs, investigating the influence on the network performance of the maximum number of wavelengths per fiber W restoration strategies, node functionality, and physical topology. Fiber requirements are analyzed for numerous network topologies both without and with link failure restoration, considering different optical cross-connect (OXC) configurations and terminal functionalities. An integer linear program (ILP) formulation is presented for the exact solution of the routing and wavelength allocation (RWA) problem, with minimal total number of fibers, F_T (W). Lower bounds on F_T(W) are discussed, and heuristic algorithms proposed. Three restoration strategies are considered and compared in terms of capacity requirement. Different network topologies are analyzed, to evaluate the influence of physical connectivity and network size on the restoration capacity. Network evolution in terms of growth in traffic demand is investigated to study the importance of wavelength conversion within the OXC's as a function of network size and connectivity, traffic demand, and wavelength multiplicity W