This paper presents methods for recovering from channel failures, link failures, and node failures in a wavelength-division multiplexed (WDM) ring network, with limited wavelength conversion capabilities at the nodes. Different recovery schemes are presented to handle each type of failure. Each scheme is evaluated based on the network hardware configuration required to support it, and the performance and management overheads associated with fault-recovery. Keywords: Optical networks, fault-tolerance, self-healing rings. This work was supported in part by grant MDA 972-95-C-0001 from ARPA. 1 Introduction Today's telecommunications infrastructure is based on SONET/SDH self-healing rings. To increase the bandwidth of their trunks, the carriers are actively deploying wavelength-division-multiplexed (WDM) pointto -point links. It is likely that WDM ring networks will come next, as a natural evolution of WDM links and SONET rings. A WDM network provides lightpaths. A lightpath is an en...

) T. Eilam S. Moran S. Zaks Department of Computer Science The Technion Haifa 32000, Israel email: feilam,moran,zaksg@cs.technion.ac.il We are motivated by the developments in all-optical networks -- a new technology that supports high bandwidth demands. These networks provide a set of lightpaths which can be seen as high-bandwidth pipes on which communication is performed. Since the capacity enabled by this technology substantially exceeds the one provided by conventional networks, its ability to recover from failures within the optical layer is important. In this paper we study the design of a survivable optical layer. We assume that an initial set of lightpaths (designed according to the expected communication pattern) is given, and we are targeted at augmenting this initial set with additional lightpaths such that the result will guarantee survivability. For this purpose, we define and motivate a ring partition survivability condition that the solution must satisfy. Generally...

1 List of Figures 3 List of Terms 5 1 Introduction 6 1.1 Background : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 6 1.2 The Virtual Topology Design Problem in All-Optical Networks : : : : : : : : 8 1.2.1 Background, Definitions and Goals : : : : : : : : : : : : : : : : : : : 8 1.2.2 Contribution : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 12 1.3 The Design of Routing Strategies : : : : : : : : : : : : : : : : : : : : : : : : 13 1.3.1 Background, Definitions, and Goals : : : : : : : : : : : : : : : : : : : 13 1.3.2 Contribution : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 15 1.4 Published Work : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 16 1.5 Organization of the Work : : : : : : : : : : : : : : : : : : : : : : : : : : : : 16 I The Design of the Virtual Topology 17 2 A Formal Model 18 2.1 Survivability and the Layered Hierarchy : : : : : : : : : : : : : : : : : : : : 18 2.2 Survivability within the Opti...