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62 Deploying and Managing IP over WDM Networks physical representation of the network. Before wavelengths are set up, the management system has to determine an appropriate route through the network that complies with QoS and routing restrictions. Subsequently, the route is implemented instructing the WDM network elements or EMSs to create the cross connections. One of the most important tasks that can be performed by the management system of the network is to define the routes that the traffic will follow. In WDM networks, where connections are supported by lightpaths, there are two categories of wavelength routing: 1. Static routing. This applies to a network configuration where no wavelength conversion is possible, which means that one wavelength is required to connect both ends. Thus, the routing is fairly simple, and the path through the network is predetermined. 2. Dynamic routing. This type of network is characterized by its ability to perform wavelength conversions and thus does not require a single wavelength to connect end points. Routing in this type of network is also referred to as reconfigurable routing, and requires reconfigurability of the WDM equipment such that a path can be computed to fulfill the desired characteristics. Applying wavelength conversion, the connection blocking probability is reduced. Given the network topology and a set of end-to-end connection requests, the routing and wavelength assignment (RWA) problem, studied by [8] and others, defines the problem of determining a route and the wavelength assignment for each route request, while at the same time minimizing the number of the wavelengths. An important factor, besides the network capabilities, in the RWA problem is what type of connection requests is issued. In case of static traffic, the connection requests are known in advance, while in case of dynamic traffic, connection requests arrive randomly. The RWA problem for static traffic is also referred to as the static lightpath establishment (SLE) problem. In general, the RWA problem is tightly coupled with the virtual (logical) topology design. The latter resolves the connectivity between different nodes, taking into consideration a set of restrictions like traffic demands matrices, nodal resources, policy constraints, and overprovision constraints. However, it can be assumed that the virtual topology design generally deals with long-term concerns, and it provides input to the RWA problem. The RWA problem itself can be further decomposed into two subproblems: route selection and wavelength assignment. The RWA problem is further complicated by different constraints, such as:
• Wavelength continuity. Two connections with the same wavelength cannot be supported on a given fiber. This constraint is of importance in networks that do not have any wavelength conversion capabilities. • Limited wavelength conversion capabilities. Not all wavelengths can be converted to any other wavelength at any OXC; frequently the conversion capabilities of OXCs are limited. • Physical impairments. These constraints are associated with the degradations that the optical signals could suffer due to either linear or nonlinear effects. Many optimization schemes have been proposed [9, 10], which try to minimize various cost functions such as the number of wavelength, blocking probabilities for different network capabilities, and traffic types. Usually, a complete set of desired source-destination requests is given and routing decisions are made for all source-destination pairs in order to achieve a global optimum solution. This solution requires complicated computation, and it becomes excessively time consuming as the network size increases. Therefore, it can be used only for static traffic requests. To cope with real-time requests, dynamic traffic that may arrive at random times, dynamic routing schemes have been proposed. These approaches lead to greater blocking probabilities, because channels are routed as they arrive. Channel rerouting is then needed in order to optimize the network utilization. This is done by reallocating the network resources. Currently, there is no standardized RWA algorithm. 4.4.2 Fault Management Management of the WDM Network Layer 63 Network survivability is an important factor in the design of a network, and network operators take special actions in order to minimize the disruption of the network traffic in case of a fiber defect or an equipment failure. Taking into consideration that a fiber cut affects thousand of connections, the existence of a flexible, efficient, and robust protection/restoration mechanism is of primary importance. Protection switching in the optical layer has many similarities with the SONET/SDH approach and achieves fast restoration/protection within 50 msec. Protection can be performed either at an optical channel level, protecting individual lightpaths, or at the aggregate signal level, which corresponds to the OMS. We can further distinguish protection at the link or the connection/path level. At the link level, the traffic is diverted where the affected link is located,
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Deploying and Managing IP over WDM
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Deploying and Managing IP over WDM
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Contents Foreword xv Preface xix Ac
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Contents vii 4.2 The WDM Network El
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Contents ix 8 Management System Des
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Contents xi 10.3 The WINMAN Testbed
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Contents xiii 13.4.1 Adoption of Op
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xvi Deploying and Managing IP over
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Preface The integration of the Inte
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Coauthors of the IST-OPTIMIST proje
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1 Introduction 1.1 The Importance o
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communications. These legacy networ
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Within these programs, consortia of
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8 Deploying and Managing IP over WD
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10 Deploying and Managing IP over W
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8 Management System Design and Impl
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Management System Design and Implem
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checking is done at the very beginn
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8.4.1 The Inventory Model The inven
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for any of the three WINMAN NMSs. T
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11 Evaluation of IP over WDM Manage
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Evaluation of IP over WDM Managemen
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system will still perform without i
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11.5.3.1 General Remarks The manage
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12 Integration of IP over WDM: The
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domains with different management t
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Integration of IP over WDM: The LIO
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ClientCTP Integration of IP over WD
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AstnTrail AstnTTP NL resource Integ
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12.4.1.1 TILAB Equipment Integratio
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12.4.1.3 Tellium Equipment Integrat
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At least two other possible solutio
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13 Future Developments and Challeng
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Future Developments and Challenges
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About the Editors Joan Serrat recei
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