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256 Deploying and Managing IP over WDM Networks would allow routers to advertise their network’s IP prefixes to the optical network and to receive external IP address prefixes from the optical network. Note that IP address prefixes within the optical network are not advertised to routers using BGP. Once a border OXC has received external IP prefixes from a router, it does not need to propagate the OXC address further, but it is responsible for keeping the association between external IP addresses and egress OXC addresses. When a certain external IP address is to be reached, the border router determines if a new optical path has to be established to the appropriate egress OXC. Special BGP mechanisms are to be determined for propagating egress OXC addresses. Integrated routing is supported by the peer-interconnection model. According to this model, the same instance of an IP routing protocol is run in both IP and optical domains. The OSPF protocol can be employed with suitable optical extensions that take into account optical link parameters and any constraints specific to optical networks. For both the augmented and peer models, a uniform IP addressing scheme across both IP and WDM layers can be provided by an integrated MPLS-based control plane. Because identical information is maintained by all OXCs and routers on both network topology and link states, a router can compute an end-to-end path to another router across the optical network. However, under the integrated routing approach, each router is responsible for maintaining a big amount of information specific the optical domain. Additionally, optical path restoration within the optical network may be visible to all nodes. Thus, integrated routing may involve significant overhead in network management. This approach may be more practical in the longer term for deployment in fast-switched or packetswitched WDM networks. Note that regardless of the interconnection model, an IP network virtual topology achieved by interconnecting IP and WDM layers raises an issue of network scalability. The provision of a full-mesh IP virtual topology, allowing for one-hop IP connectivity (either via an IP link or via an optical path), is restricted by the number of router interfaces and OXC channels. If the full-mesh virtual topology cannot be supported (which can be the case for a network that has evolved into a large IP/WDM backbone), a multihop IP routing scheme will be necessary under the overlay model. Two layer IP MPLS over WDM MPλS stacking will be needed under the augmented and peer models, while generalized MPLS (GMPLS) architecture can be deployed to provide both packetbased and non-packet-based forwarding planes. 13.3.2 Dynamic Routing and Wavelength Conversion in the Optical Domain The routing of optical paths in a dynamic way, inherent to the IP over reconfigurable WDM model, can be carried out by an extension of a link state routing
Future Developments and Challenges for IP over WDM Network Deployment 257 protocol such as OSPF or IS-IS, as is used for IP routing [2]. However, in contrast to traffic-independent routing in IP layer, wavelength routing should be performed while taking into account changes in traffic load, so that path blocking due to unavailability of a free wavelength in the most congested link is minimized. High blocking of optical paths leads to dramatic increase in both packet loss rate and end-to-end delays, thus degrading performance of the whole network. The issue of optimal routing in the optical domain is referred to as the RWA problem. While the RWA problem is shown to be MP complete [3], special heuristics such as first-fit, least-used, or most-used assignment can significantly improve the performance in terms of blocking probability [4]. Therefore, RWA computation schemes should be supported by the routing protocols. In order to distribute information on wavelength loading, the routing protocols must be extended to represent this parameter in the link state advertisement updates. Wavelength conversion capability is another problem that affects RWA performance. On the one hand, it can reduce optical path blocking probability. However, this technology is immature and expensive at present. Thus, full wavelength conversion capability is unlikely to be deployed. Instead, limited wavelength conversion can be supported where a very small number of converters are optimally placed to minimize blocking [5]. Additionally, the converters can be placed at the age of a network administrative domain to reduce the information correlation and dependencies across the domain. Depending on the capability of the deployed cross connects, routing algorithms might have to explicitly manage wavelength continuity constraint. Thus, link state advertisement updates should support more detailed RWA information. 13.3.3 IP/WDM Fault Management As each optical path is expected to transport of hundreds of gigabits in the near future, survivability of IP/WDM networks is a key factor to their successful deployment. Issues arising from the provision of reliable services fall into two main categories, fault localization and fault recovery. Fault localization is one of the most difficult issues associated with IP/WDM networks with a reconfigurable optical core. In order to monitor the WDM layer, low-level analog signal parameters such as optical signal power and optical signal-to-noise ratio need to be constantly measured. It is difficult to map quantitatively these parameters to higher level IP layer observable properties such as packet loss rate. The observable IP layer outcome can be completely different, depending on a threshold value set by the NMS to generate a specific fault alarm. Additionally, the threshold values tuned to a certain bit rate may be too restrictive for lower rate signals in terms of the number of alarms generated
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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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4 Management of the WDM Network Lay
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λ1λ 2 ··· λ w λ1λ 2 ···
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Management of the WDM Network Layer
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• Lightpaths that may be protecte
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• Wavelength continuity. Two conn
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4.4.4 Management Interfaces Managem
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5 IP Over WDM Integration Mechanism
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STM1/ATM interface requirements. Fo
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IP router OLA The version of IP ove
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Gigabit Ethernet interface GbE prov
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the IETF extended the MPLambdaS fra
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ASON/ASTN. ITU-T will try to push t
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The proposed management solution is
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IP Over WDM Integration Mechanisms
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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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