metro optical network continues to focus primarily on legacy DS1 and DS3 granularity within the metropolitan area network (MAN) and through the backbone. A full-featured metro WDM must support both the traditional interfaces as well as the new data interfaces. Enterprise routers currently support direct OC-3c, OC-12c, and OC-48c/192c WAN links. These private-line interfaces on end-user equipment (that is, on intranet routers) are widely deployed because of their ubiquitous deploy- ment throughout metro optical networks (for example, the extensive deployment of SONET transport and crossconnects). However, this comes at a cost. High-end SONET plug-ins can cost up to $50,000. Therefore, it is desirable to include these interfaces in the NE because of the economies of scale that can be secured by network providers, which can then be passed onto the enterprise user. Equipment vendors working on WDM are realizing that data-oriented services are now consuming more network capacity than voice due to an Chapter 5 increasing number of users and escalating capacity demands from each user. The protocols, bit rates, and interfaces used by the enterprise net- works that support these applications are different from those used in the carrier networks. The former are increasingly Ethernet based; the latter are typically OC-x based. Conversion between the two domains is needed. The user can affect that conversion, but it has to be done at multiple places where the enterprise network touches the carrier's network or, better yet, it can be done by the carrier on behalf of the user. One example may suffice. Carriers have come to realize that it is better to carry voice over distances in digital format. However, the network does not impose that requirement to the user. All residential users generate analog voice over their telephone handsets and the network adapts the user's signal into a digital signal that is better suited for network handling. Similarly, because all enterprise net- works are now based on Ethernet/IP/TCP technology