 ship to the SONET frame, or framing structure. First the five layers are described: The media layer (also called photonic on fiber) is the physical media in the form of a conductor for the signal. In practice, the signal traveling over the conductor is either radio or light wave energy. The section layer carries STS frame and section overhead information such as error monitoring and scrambling. Line layer contains the synchronous payload envelope (SPE) and its overhead. The SPE basic channel is a 51.840-Mbs continuous bitstream. This stream takes on a OC or STS label. For example, a single stream is called an OC-1 if it is an optical signal, or STS-1 if it is an electrical signal. This basic channel can be multiplexed with others running at the same rate into higher order streams. When this happens, it takes on a number indicating the number of basic streams, such as OC-3 or STS-3, running at 155.520 Mbs. The STS layer lies between the line layer and the virtual tributary layer. This is the demarcation between legacy T-carrier (T1, E1, E3, DS3) signals, functions, and services, and SONET functions and services. VT layer is the interface between SONET and legacy T-carrier net- work facilities. A block diagram of a multi-section SONET/SDH layer is shown in Figure 4-6. The level of detail includes the basic components of a typical link. Each of these components are defined and described in terms of their relationship to each other and what they contribute to overall link function and performance. SONET link components include the media, repeaters, light wave terminating equipment (LTE), and terminal multiplexer (TM). 4 NETWORK TECHNOLOGY AND METHODOLOGY Virtual Tributary Layer STS Layer Line Layer Section Section Section Section Section Section FIGURE 4-6 Basic SONET Link Block Diagram Components in the media layer include fiber cable with multiple fiber conductors, regenerators, light wave amplifiers, conduit, poles, and other supporting structure. If a facility uses regenerators, it will not include light wave am