As the Internet and network technologies evolve, the IP over WDM solution has been envisioned as the most promising solution for the next generation Internet architecture. So survivability in IP/WDM networks becomes critical for the success of the next generation Internet architecture. Considerable research efforts have been dedicated to studying the survivability in IP/GMPLS and WDM network respectively, but still remains the need for a better understanding of the interworking, coordination and functionality partitioning in survivability between IP and WDM. In this paper, we explore the necessity, methods and advantages to coordinate multi-layer survivability in IP/WDM network. We especially focus on the study of the escalation method, multi-layer network spare capacity design and function partitioning. We study the use of differentiated survivability policies combined with a multi-layer survivability scheme for IP/WDM networks.

A network is said to be survivable if it has sufficient capacity for rerouting all of its flow under the failure of any one of its edges. Here we present a polyhedral approach for designing survivable networks. We describe a mixed–integer programming model, in which sufficient slack is explicitly introduced on the directed cycles of the network while flow routing decisions are made. In case of a failure, flow is rerouted along the slacks reserved on directed cycles. We give strong valid inequalities that use the survivability requirements. We present a computational study with a column–and–cut generation algorithm for designing capacitated survivable networks.

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.

This work introduces a significant extension to the method of p-cycles for network protection. The main advance is the generalization of the p-cycle concept to protect multi-span segments of contiguous working flow, not only spans that lie on the cycle or directly straddle the p-cycle. This effectively extends the p-cycle technique to include path protection or protection of any flow segment along a path as well as the original span protecting use of p-cycles. It also gives an inherent means of transit flow protection against node loss. We develop a capacity optimization model for the new scheme and compare it to prior p-cycle designs and other types of efficient mesh-survivable networks. Results show that path-segment-protecting p-cycles ("flow p-cycles" for short) have capacity efficiency near that of a path-restorable network without stub release. An immediate practical impact of the work is to suggest the use of flow p-cycles to protect transparent optical express flows through a regional network.

Abstract A recently proposed concept for dynamic provisioning of survivable lightpath services, called the protected working capacity envelope (PWCE) is considered from a network capacity design and blocking standpoint. The PWCE concept offers several attractive properties for a next-generation Internet based on“IP over optical”transport in which transport level connections can be independently and rapidly requested and released by service layer nodes. The main advantages of PWCE are simplification of the state databases and signaling involved for protection considerations in such dynamically operating transport networks. This chapter reviews the concept and related background. It then develops and tests models for the design of PWCEs involving the optimized partitioning of installed capacity into a working envelope, for simple and rapid service provisioning, and a separate reserve network which is configured into a set of p-cycles that provides 100 % restorability to the envelope. 1.

Abstract. Connection availability is considered as a critical metric, when providing differentiated services in WDM mesh networks. Indeed, one of the major concerns of optical network operators is related to improving the availability of services provided to their highest-class clients. Achieving this objective is possible through the use of the different classical protection schemes, namely the so-called dedicated and shared protection schemes. However, the majority of the work concerning protection schemes has considered the primary connections as equally important when contending for the use of the backup resources. As a main contribution in this paper, we therefore propose an improvement of the existing protection schemes through the introduction of relative priorities among the different primary connections contending for the access to the protection path. To evaluate numerically the benefits of the service differentiation feature introduced in our proposal, we first develop a mathematical model based on which we derive explicit expressions for the average connections availabilities that result from both the classical protection schemes and the proposed priority-aware one. Through this model, we show how the availability of the highest-class clients is improved when deploying the proposed priority-aware protection scheme. Finally, with the same objective in mind, we develop a simulation study, where a given set of connection demands with predefined availability requirements is provisioned, using different protection strategies. Through this study, we show that the priority-aware protection strategy satisfies service-availability requirements in a cost-effective manner compared with the classical protection schemes. 1

In this paper, we study restoration mechanisms to handle channel and link failures in an optical WDM wavelength-routed wide-area backbone network based on a mesh topology. The solution uses a small number of tunable lasers per link to provide restoration capability. In addition to link failures, we consider individual channel failures which might occur when one or more transceivers fail at the source of the lightpath or due to a failure in the switch fabric. Restoration is first attempted using the tunable lasers to transmit on the failed wavelengths. If all the failed lightpaths cannot be restored using the tunable lasers, unused wavelengths on the same link are used (this requires optical wavelength conversion at the nodes). For the remaining lightpaths requiring restoration, link-level restoration mechanisms are attempted. Two different link-level mechanisms are presented: redirection algorithm (RDA) and disjoint path algorithm (DPA). These mechanisms use WDM-specific link information to compute the link restoration routes. We present results based on discrete-event simulations to understand the performance of the proposed mechanisms, in terms of restoration efficiency and restoration times. The results show that for networks of varying size and node degree with 32 wavelengths on each link, using as few as 8 tunable lasers per link provides good restoration efficiency under moderate traffic load.

(Communicated by Yiju Wang) Abstract. As a generalization of the traditional path protection (PP) scheme in WDM networks where a backup path is needed for each active path, the partial path protection (PPP) scheme uses a collection of backup paths to protect an active path, where each backup path in the collection protects one or more links on the active path such that every link on the active path is protected by one of the backup paths. While there is no known polynomial time algorithm for computing an active path and a corresponding backup path using the PP scheme for a given source destination node pair, we show that an active path and a corresponding collection of backup paths using the PPP scheme can be computed in polynomial time, whenever they exist, under each of the following four network models: (a) dedicated protection in WDM networks without wavelength converters; (b) shared protection in WDM networks without wavelength converters; (c) dedicated protection in WDM networks with wavelength converters; and (d) shared protection in WDM networks with wavelength converters.

this paper, we therefore propose an improvement of the existing protection schemes through the introduction of relative priorities among the different primary connections contending for the access to the protection path. To evaluate numerically the benefits of the service differentiation feature introduced in our proposal, we first develop a mathematical model, based on which we derive explicit expressions for the average connection availabilities that result from both the classical protection schemes and the proposed priority-aware one. Through this model, we show how the availability of the highest-class clients is improved when deploying the proposed priority -aware protection scheme. Finally, with the same objective in mind, we develop a simulation study, where a given set of connection demands with predefined availability requirements is provisioned using different protection strategies. Through this study, we show that the priority-aware protection strategy satisfies service-availability requirements in a cost-effective manner compared with the classical protection schemes. Copyright 2006 John Wiley & Sons, Ltd

Resilience to failures and deliberate attacks is becoming an essential requirement in most communication networks today. This also applies to P2P Overlays which on the one hand are created on top of communication infrastructures, and therefore are equally affected by failures of the underlying infrastructure, but which on the other hand introduce new possibilities like the creation of arbitrary links within the overlay. In this article, we present a survey of strategies to improve resilience in communication networks as well as in P2P overlay networks. Furthermore, our intention is to point out differences and similarities in the resilience-enhancing measures for both types of networks. By revising some basic concepts from graph theory, we show that many concepts for communication networks are based on well-known graph-theoretical problems. Especially, some methods for the construction of protection paths in advance of a failure are based on very hard problems, indeed many of them are in NP and can only be solved heuristically or on certain topologies. P2P overlay networks evidently benefit from resilienceenhancing strategies in the underlying communication infrastructure, but beyond that, their specific properties pose the need for more sophisticated mechanisms. The dynamic nature of peers requires to take some precautions, like estimating the reliability of peers, redundantly storing information, and provisioning a reliable routing. 1