The appearance of enhanced multimedia services requiring huge bandwidths, such as broadcast highdefinition television (HDTV) and video-on-demand, created aneed for transitioning from basic interconnected rings to extremely high-capacity rings adjoined to mesh networks that can support clusters of up to 50 nodes in a metropolitan area. Therefore another network element with more sophisticated switching capabilities than a ROADM is needed. This element, which is called an optical crossconnect (OXC) provides switched pass-through paths for express traffic that does not terminate at the node and an interface for dropping and adding optical signals at the node. The express traffic can de switched from any input to any output fiber. Internally such a device can have either an electrical or optical switching fabric. To understand basic optical switching technology, sec. 13.6.1 looks at general OXC configurations, sec. 13.6.2 considers the performance impact when wavelength conversion is used, and sec. 13.6.3 describes the standard implementations of wavelength routing or optical circuit switching.