This paper is an introduction to survivability of WDM networks. All the main optical protection techniques proposed as far as now for the WDM layer are classified and reviewed. In particular, commonly adopted protection strategies for ring and mesh networks are explained. Moreover, off-line planning of WDM networks able to support path protection is briefly introduced. Finally, an example of heuristic networkcapacity optimization is presented, discussing results obtained by considering a case-study network.

) T. Eilam S. Moran S. Zaks Department of Computer Science The Technion Haifa 32000, Israel email: feilam,moran,zaksg@cs.technion.ac.il We are motivated by the developments in all-optical networks -- a new technology that supports high bandwidth demands. These networks provide a set of lightpaths which can be seen as high-bandwidth pipes on which communication is performed. Since the capacity enabled by this technology substantially exceeds the one provided by conventional networks, its ability to recover from failures within the optical layer is important. In this paper we study the design of a survivable optical layer. We assume that an initial set of lightpaths (designed according to the expected communication pattern) is given, and we are targeted at augmenting this initial set with additional lightpaths such that the result will guarantee survivability. For this purpose, we define and motivate a ring partition survivability condition that the solution must satisfy. Generally...

In IP-over-WDM networks, a logical IP network is routed on top of a physical optical fiber network. An important challenge hereby is to make the routing survivable. We call a routing survivable if the connectivity of the logical network is guaranteed in 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.

Abstract — In IP-over-WDM networks, a logical IP network has to be routed on top of a physical optical fiber network. An important challenge is to make this routing survivable. We call a routing survivable if no single physical link failure can disconnect the logical topology. In this paper we present FastSurv, a local search algorithm for survivable routing. FastSurv works in an iterated way: 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. We also extend the algorithm to take link capacity constraints into account. We show that our simple algorithm can produce better and faster results than current state-of-the-art algorithms. I.

Abstract—In layered networks, a single failure at a lower layer may cause multiple failures in the upper layers. As a result, traditional schemes that protect against single failures may not be effective in cross-layer networks. In this paper, we introduce the problem of maximizing the connectivity of layered networks. We show that connectivity metrics in layered networks have significantly different meaning than their single-layer counterparts. Results that are fundamental to survivable single-layer network design, such as the Max-Flow Min-Cut theorem, are no longer applicable to the layered setting. We propose new metrics to measure connectivity in layered networks and analyze their properties. We use one of the metrics, Min Cross Layer Cut, as the objective for the survivable lightpath routing problem, and develop several algorithms to produce lightpath routings with high survivability. This allows the resulting cross-layer architecture to be resilient to failures. I.

This paper is an introduction to survivability of WDM networks. All the main optical protection techniques proposed since now for the WDM layer are classified and reviewed. In particular, commonly adopted protection strategies for ring and mesh networks are explained and network planning with path protection is briefly introduced.

In IP-over-WDM networks, a logical IP network has to be routed on top of a physical optical fiber network. An important challenge hereby is to make the routing survivable. We call a routing survivable if the connectivity of the logical network is guaranteed in case of a failure in the physical network. In this paper we describe FastSurv, a local search algorithm which can provide survivable routing in the presence of physical link failures. The algorithm can easily be extended for the case of node failures and multiple simultaneous link failures. In a large series of test runs, we show that FastSurv is much more scalable with respect to the number of nodes in the network than current state-ofthe-art algorithms, both in terms of solution quality and run time.

Abstract—We develop diverse routing schemes for dealing with multiple, possibly correlated, failures. While disjoint path protection can effectively deal with isolated single link failures, recovering from multiple failures is not guaranteed. In particular, events such as natural disasters or intentional attacks can lead to multiple correlated failures, for which recovery mechanisms are not well understood. We take a probabilistic view of network failures where multiple failure events can occur simultaneously, and develop algorithms for finding diverse routes with minimum joint failure probability. Moreover, we develop a novel Probabilistic Shared Risk Link Group (PSRLG) framework for modeling correlated failures. In this context, we formulate the problem of finding two paths with minimum joint failure probability as an Integer Non-Linear Program (INLP), and develop approximations and linear relaxations that can find nearly optimal solutions in most cases. I.

1 List of Figures 3 List of Terms 5 1 Introduction 6 1.1 Background : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 6 1.2 The Virtual Topology Design Problem in All-Optical Networks : : : : : : : : 8 1.2.1 Background, Definitions and Goals : : : : : : : : : : : : : : : : : : : 8 1.2.2 Contribution : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 12 1.3 The Design of Routing Strategies : : : : : : : : : : : : : : : : : : : : : : : : 13 1.3.1 Background, Definitions, and Goals : : : : : : : : : : : : : : : : : : : 13 1.3.2 Contribution : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 15 1.4 Published Work : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 16 1.5 Organization of the Work : : : : : : : : : : : : : : : : : : : : : : : : : : : : 16 I The Design of the Virtual Topology 17 2 A Formal Model 18 2.1 Survivability and the Layered Hierarchy : : : : : : : : : : : : : : : : : : : : 18 2.2 Survivability within the Opti...

Optical Fiber technology employing wavelength-division multiplexing (WDM) has and continues to be investigated and commercially deployed to meet our ever-increasing bandwidth demands. WDM partitions the huge bandwidth of an optical fiber into many non-overlapping wavelength channels, each of which can operate at the data rate of 10 Gbps (or 40 Gbps or higher). This dissertation investigates design and modeling issues of optical WDM mesh networks, as well as ring networks. This dissertation first proposes a novel generic graph model for traffic grooming in heterogeneous WDM mesh networks so that low-speed traffic streams can be “groomed ” (or carried) by high-capacity wavelength channels. This model uses an auxiliary graph to represent the network state, which can accommodate various resource constraints. It can achieve different grooming policies by employing a simple shortest-path algorithm, and it can be applied to both static and dynamic trafficgrooming scenarios. A grooming policy determines how to carry the traffic in a certain situation.