International Journal of Network Management
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We present a collection of studies related to the availability of service in mesh-restorable transport networks. The issue of service availability in transport networks is of increasing importance due to our always increasing reliance on telecommunication networks, which now requires that network operators give service-availability guarantees to their customers in the form of service level agreements (SLA). It is therefore important to study network architectures in terms of the level of service availability they provide, and not just on capacity efficiency, simplicity of operation, cost, etc. This work deals with this issue for transport networks using a mesh architecture and more specifically for dynamic mesh-restorable networks. After a long era where ring-based systems dominated the world of transport networking, the mesh architecture appears to be the solution of choice for future optical transport networks. The mesh architecture is already known for its high capacity efficiency (little capacity is required to serve demands and to guarantee restorability to failures), the simplicity of service provisioning (new service paths can usually be provisioned on shortest path), and for its good scalability (capacity only needs to be added where exhausted therefore making the network scaling easy). However, the issue of service availability in mesh-restorable networks was yet to be investigated. We first develop theoretical and practical approaches for determining the availability of service paths in mesh-restorable transport networks that are designed to be restorable to any single span-failure. This initial treatment of the problem shows the major influence that dual span-failure restorability has on service availability—the importance of considering dual span-failure scenarios is later reinforced by a study of the effects of maintenance actions on network restorability. It is also demonstrated that, despite what intuition tells us, restoration time has in fact little impact on service availability. The influence of various factors on dual-span failure restorability (and therefore on availability) is also investigated. We then present several network capacity design methods for serving demands with various restorability requirements: first considering the case of demands with higher restorability requirements (single span-failure restorability and dual span-failure restorability), and then considering a multi quality of protection environment with demands having restorability requirements ranging from single span-failure restorability down to preemptible services. The thesis also provides an initial theoretical treatment of the availability of service in networks using p-cycle protection—a new survivability scheme offering fast restoration and high capacity efficiency—, and a comparison between the availability of service with dynamic mesh-restoration and with ring-based protection. Experimental results are obtained using a set of detailed test networks of various sizes and connectivity. The results show the very high potential of mesh-restorable networks to simultaneously serve various types of availability requirements from low requirements to requirements of ultra high availability—higher than the availability of paths in ring-based networks—through the use of a multi QoP environment, and to benefit from that multi service aspect to achieve high capacity efficiency.