Optical network survivability beyond the core

Optical network survivability in the backbone, or core, network has been an active area of research. As optics move closer to the edge and to end users, the core network is now used not only to provide connections across a wide area, but also to provide connections for local and metropolitan area networks (LANs and MANs). While optical backbone networks are generally concerned with providing end-to-end circuits based upon whole wavelengths, optical LANS and MANs generally provide shared access to a small number of wavelengths. In this paper, we consider the issue of robustness for optical access networks built as overlays on optical mesh networks. The problem of optical access network robustness is that of maintaining connectivity among nodes of the access networks after a link (or possibly node). We survey three methods of providing robustness to optical access networks. The first method consists of building access networks as covers of rings. The second method builds folded bus overlays and use a combination of optical switches and electronic routers to provide reliability. The third generalizes the concept of buses to build tree-based robust collection and distribution routes over mesh networks. Optical access networks are beginning to be deployed at the edge of the optical backbone network to support access by the high-end users that drive increased bandwidth demands. This development in the applications of optical networking poses new challenges in the areas of medium access, topology design and network management. In this article, we survey access network architectures and outline the issues associated with providing reliability for these architectures.