Distributed path restoration based on optical cross-connects can provide highly capacity-efficient real-time restoration for WDM-based optical networking. However, to obtain an assured restoration level with the theoretically very low amounts of spare capacity that path restoration allows, one must solve, or closely approximate a solution to, the integer multicommodity maximum flow (MCMF) problem, MCMF is, however a hard combinatorial optimization problem due to what is called the "mutual capacity" aspects of the problem: which of many competing origin-destination pairs should be allowed paths over the finite spares on each span? Integer MCMF is further complicated by the nonunimodular nature of the problem, i.e., fractional flows are forbidden but would arise if solved by linear programming. This paper presents a heuristic principle that tests well against integer programming solutions of MCMF routing. The heuristic is first characterized in a centralized program, then adapted for use in a distributed path restoration protocol. In all test cases, the protocol obtains over 97% of the paths found in an optimal MCMF solution in the same network. Via OPNET simulation it is also predicted that the protocol will run in well under 2 seconds which means it could be used directly in real-time, or in distributed prefailure self-planning, for restoration. The significance is that network operators could aggressively optimize their spare capacity, toward theoretical minimums, while still assuring 100% restorability.

http://www.ece.ualberta.ca/~grover/pdf/Path_rest_%20DRA_JSAC.pdf

A highly efficient path-restoration protocol for management of optical network transport integrity

Synchronous optical network (SONET) technology has made high-speed self-healing ring (SHR) architectures practical and economical. The SHR architectures can be divided into two basic classes: bidirectional SHR (B-SHR) and unidirectional SHR (U-SHR). The cost and capacity tradeoffs between B-SHRs and U-SHRs depend strongly on the application, the network size, and the demand pattern. B-SHRs with four fibers can be operated under today's operations environment without a significant change. However, U-SHRs using a path protection switching method may ease intervendor compatibility problems and can be implemented on a timely basis without changing the well-defined SONET APS protocol. The selection of appropriate SONET SHR architectures will depend on the operating telephone companies' economic analysis, emphasis on a multivendor environment, SHR implementation time frame, and standards progress on making change to support a bidirectional ring architecture. >

https://ieeexplore.ieee.org/iel5/516/3389/00116552.pdf

A class of self-healing ring architectures for SONET network applications

Publisher Summary Network reliability encompasses a range of issues related to the design and analysis of networks which are subject to the random failure of their components. Relatively simple, and yet quite general, network models can represent a variety of applied problem environments. Network classes for which the models are discussed are particularly appropriate include data communications networks, voice communications networks, transportation networks, computer architectures, electrical power networks and command and control systems. The ultimate objective of research in the area of network reliability is to give design engineers procedures to enhance their ability to design networks for which reliability is an important consideration. Ideally, one would like to generate network design models and algorithms which take as input the characteristics of network components as well as network design criteria, and produce as output an "optimal" network design.

Chapter 11 Network reliability

To protect against possible network node or link failure and achieve high reliability of communications, pre-planned failure recovery schemes are needed in modern high-speed communication networks. A couple of schemes have been previously reported for multicast communications. We present a scheme based on a "dual-tree" structure in which a secondary tree for fault-tolerance purpose is built as a complement to a primary multicast tree. The secondary tree provides alternative delivery paths that can be activated when link or node failure is detected in the primary multicast tree. Simulation experiments show that this scheme has shorter restoration time and cause less multicast tree cost increase after restoration than some schemes proposed previously.

http://nrlweb.cs.ucla.edu/publication/download/96/2001-icc-1.pdf

A "dual-tree" scheme for fault-tolerant multicast

A cutting plane algorithm for computing k-edge survivability of a network

At the transport layer in interoffice and interexchange networks, shared protection rings (SPRINGS) interconnected at matched nodes can provide 100% restoration in milliseconds after cable cuts and central office failures. The author introduces the SPRING and explains how its capacity advantage over other ring configurations enables it to be the most economical solution in more applications. Transport restoration technologies-1+1 diversity, digital crossconnect systems, and SPRINGS-in interoffice and interexchange environments are compared. A representative network study is presented to justify the choice of SPRINGs and matched nodes for the target architecture. Recommendations on how to evolve today's asynchronous networks in preparation for a fully survivable SONET ring-based network are also provided. Generic ring planning guidelines and network examples are presented to demonstrate how today's networks can be evolved to provide end-to-end survivable SONET transport. An approach to ring-based network design that simplifies the planning process and minimizes network cost is provided. >

T. Flanagan

Papers

Fiber network survivability