Like any other standard networking technology, WAN transmission facilities feature standardized transmission schemes. Such schemes define transmission rates and media types, as well as framing formats and multiplexing methodologies. There are many such schemes and they vary by both geography and technology. Some of the more commonly encountered standards include the following:
ANSI's Digital Signal Hierarchy
ITU's Digital Signal Hierarchy
SONET's Optical Carrier System
SONET's Synchronous Transport Signal System
These standards are implemented in carrier systems. The remainder of this chapter provides an overview of some of the more useful signaling standards, as well as the carrier systems that are their physical embodiment. ...