ABSTRACT
This chapter, together with Chapter 19, on optical transport networks, reviews the evolution of optical networks from the architectural and signal transport perspectives, respectively. The architectural delineation of optical networks can be considered from various geographical domains, multiplexing technologies, switching and routing functions, and transport capacity and technologies. Today, a revolution has occurred from earlier single-wavelength synchronous optical net (SONET)/synchronous digital heirarchy (SDH)-based point-to-point transport to various phases of multi-wavelength optical transmission networking and subsequent bandwidth explosion via advances in dense-wavelength division multiplexing (DWDM). Currently, an interconnection of various point-to-point optical links based on SONET/ SDH rings, trees, and optical mesh topologies constitute the optical networks
infrastructure. However, the evolution of the optical networks toward more flexible, survivable, scalable, and interoperable architectures is ongoing as we write these chapters. Despite all progress in the optical transport from high-speed TDM (OC-192) and DWDM, true all-optical networks have yet to be realized. In limited cases, long-haul and metro-area networks have achieved some wavelength-routing capabilities.
