Differentiated Reliability (DiR) in Multi-layer Optical Networks

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Current optical networks typically offer two degrees of service reliability: full (100%) protection (e.g., in presence of a single fault in the network) and no (0%) protection. This reflects the historical duality that has its roots in the once divided telephone and data environments, in which the circuit oriented service required protection, i.e., provisioning readily available spare resources to replace working resources in case of fault, while the datagram oriented service relied upon restoration, i.e., on dynamic search for and reallocation of affected resources via such actions as routing table updates. The current trend, however, is gradually driving the design of networks towards a unified solution that will support, together with the traditional voice and data services, a variety of novel multimedia applications. Evidence of this trend over the last decade is the growing importance of concepts, such Quality of Service (QoS) and Differentiated Services to provide varying levels of service performance in the same network. According to the fact that today's competitive networks can no longer provide only pure voice and datagram services, the historical duality between fully protected and unprotected (100% and 0% reliability in case of a single fault) is rapidly becoming obsolete. Modern networks can no longer limit the options of reliability only to these two extreme degrees. On the other hand, while much work is being done on QoS and Differentiated Services, surprisingly little has been discussed about and proposed for developing differentiated network reliability to accommodate this change in the way networks are designed. In this proposal, the researchers proposed to address the problem of designing cost effective multi-layer network architectures that are capable of providing various reliability degrees (as opposed to 0% and 100% only) as required by the applications. In the proposal, the concept of Differentiated Reliability (DiR) is for the first time formally introduced and applied to provide multiple reliability degrees (classes) in the same layer using a common protection mechanism, e.g., line switching or path switching. According to the DiR concept, each connection in the layer under consideration is assigned a minimum reliability degree, defined as the probability that the connection is available at any given time. The overall reliability degree chosen for a given connection is determined by the application requirements. In a multi-layer network, the lower layer can thus provide the above layers with the desired reliability degree, transparently from the actual network topology, constraints, device technology, etc. The cost of the connection depends on the chosen reliability degree, with a variety of options offered by DiR. The proposed research explores the multifaceted aspects of DiR-based design of multi-layer optical networks, with specific emphasis on the IP/WDM architecture. Optimally designing a DiR network is in general extremely complex and will require special techniques tailored to handle it with acceptable computational time. Therefore, along with research on the architecture and modeling of DiR-based networks the researchers propose a powerful novel discrete optimization paradigm to efficiently handle the difficult tasks. The optimization approach is based on adopting and adjusting the Fourier Transform technique for binary domains. This unique technique makes it possible to realize an efficient "filtering" of the complex design/optimization problem, such that the solution becomes computationally feasible, while still preserving sufficient accuracy.