to as the "perfect network," and measure performance. And of course there are ways to measure and characterize the performance of the facilities and service making up the link between the sites. Now we go to details of network architecture, facilities, and services. End-To-End Content Transport Service Internet/Telecom Equipment & Facilities Network Broadcast Switching Network Broadcast Interface Access Access Interface Facility Device Transport Device Facility FIGURE 5-3 End-to-End Service Reference Model PRACTICAL IP AND TELECOM FOR BROADCAST ENGINEERING AND OPERATIONS NETWORK ARCHITECTURE DESCRIPTION Communications network architecture is generally thought of in terms of access, interface, geographic coverage, media type, and signaling or control systems. The basic functional parts of the net- work architecture are premises, equipment, access, and transport facilities. Access and transport facilities are made up of routing, switching, transmission, clocking, and network management elem- ents. Today's network as well as the network of the foreseeable future will continue to carry voice, data, video, and the Internet. Today's network includes the Internet and the global public and private telecommunications network it is built on. Within that network are facilities based on wire (coaxial and fiber), terrestrial and satellite wireless technology, and methods. LAYERING AS USED IN COMPUTERS AND COMMUNICATIONS NETWORKS The basic idea behind layering is that computer equipment and system functions are bound by, or within, layers. Each layer is bound to, or interacts with, its neighbor immediately above and below. If each layer up and down the stack interacts, or interoperates, with its neighbor successfully, then the system or process making up the overall system or network is likely to succeed in performing all the functions it was designed to accomplish. The layering concept was created by the International Standards Or- ganization to serve as a standard definition of computer industry structure dealing with commun