7 Chapter - WDM Network Elements

Abstract

This chapter discusses the basic network elements constituting wavelength division multiplexing (WDM) networks. The WDM network provides circuit-switched lightpaths that can have varying degrees of transparency associated with them. Wavelengths can be reused in the network to support multiple lightpaths as long as no two lightpaths are assigned the same wavelength on a given link. Lightpaths may be protected by the network in the event of failures. Lightpaths can be used to provide flexible interconnections between users of the optical network, such as Internet protocol (IP) routers, allowing the router topology to be tailored to the needs of the router network. An optical line terminal (OLT) multiplexes and demultiplexes wavelengths and is used for point-to-point applications. It typically includes transponders, multiplexers, and optical amplifiers. Transponders provide the adaptation of user signals into the optical layer. An optical add/drop multiplexer (OADM) drops and adds a selective number of wavelengths from a WDM signal, while allowing the remaining wavelengths to pass through. Several types of OADMs are possible with a range of capabilities based on the number of wavelengths they can add and drop. An optical crossconnect (OXC) is the other key network element in the optical layer. OXCs are large switches used to provision services dynamically as well as provide network restoration. OXCs are typically deployed in a mesh network configuration.