ces. In practice, WANs typically interface to an SDH transport network. However, because SDH was originally conceived to transport 64-kbit/s voice circuits, it can be very inefficient for trans- porting data packets. Subsequently, many equipment vendors at the turn of the century produced proprietary solutions that optimized packet transport over SDH networks. Unfortunately, this led to large-scale incompatibility, and the International Telecommunication Union (ITU) was forced to undertake the process of augmenting the existing SDH recommendations with three internationally agreed on techniques that have made SDH more "data friendly." These new features are often collectively referred to as "next generation" and consist of Virtual Concatenation (VCAT), Link Capacity Adjustment Scheme (LCAS), and Generic Framing Procedure (GFP). The advantage of these features is that they can be implemented as inter- face cards at the edge of an existing SDH network and therefore offer a piecemeal upgrade process to incumbent operators who are experiencing relentless growth of their packet- based services. In this way, next-generation SDH offers a solution to increase the lifetime of the existing SDH infrastructure to transport packet data more efficiently without radical changes to the underlying transport network and without sacrificing the tried and trusted OAM&P features of SDH. Concatenation Concatenation is the process of combining X SDH containers into a larger container that provides a bandwidth X times bigger than an individual container. Both low-order contain- ers (e.g., VC-11, VC-12, and VC-2) and high-order containers (e.g., VC-3, VC-4) can be con- catenated in either contiguous or virtual concatenation modes. Although VCAT is one of the main features of NG-SDH, contiguous concatenation in SDH networks will be briefly described for comparative purposes. Contiguous Concatenation Contiguous concatenation was conceived in the early days of SDH to accommodate high- speed data applications that use protocols such as Async