 wavelength division multiplexers and ROADMs. ROADMs offer several key advantages. First, as the name suggests, they enable bandwidth assignment to be configured on an as-needed basis rather than having to be determined in advance, prior to rollout. Second, remote configuration and reconfiguration are possible. Finally, ROADMs accommodate automatic power bal- ancing, a much-needed capability because it is not always known in advance where a signal may be routed, and power balancing of the signals is therefore not only required but necessary. Optical Switches Optical switches, sometimes referred to as optical cross-connects or wavelength routers, are devices that reside at junction points in optical backbones and enable carriers to string together wavelengths to provide end-to-end connections (see Figure 11.6). They link any of several incoming lines to any of several outgoing lines and auto- matically reroute traffic when a network path fails. An optical switch is the optical version of a general-purpose switch that provides flexibility and reliability in today's PSTN. Optical switches move transmissions between fiber segments and also enable some network management activities, including optical-layer restoration and reconfiguration, dynamic wavelength management, and automated optical-layer provisioning. End-to-End Optical Networking Connection Points Wavelength 1 Wavelength 1 Wavelength n Wavelength n Optical or DWDM Systems Electrical DWDM Systems Switch Core Wavelength 1 Wavelength 1 Wavelength n Wavelength n Figure 11.6 An example of an optical switch There are three key issues in selecting optical switches: Number of ports-Carriers are looking for devices that can scale to more than 1,000 ports. Automation-Carriers want to provision strings of wavelengths from a remote console in real-time. Granularity-Carriers want a switch to handle small as well as large band- widths SO that they can eliminate multiplexers. First- and Next-Generation Optical Switches Two types of optical switches are currently being prod