today and are likely to remain SO well into the future. Signaling is the mechanism whereby customers, subscribers, and users (through equipment) communicate with the network to setup and tear down a connection, or configure it for initial use, or re- configure it for different use (i.e., change the default service configur- ation). Signaling is also a process whereby network elements com- municate with each other in response to commands from users for service, or the owner for changes in configuration or service capabil- ity. Successful signaling depends on a logical addressing or numbering scheme whereby all the elements in and outside the network carry a unique identification label. Switching has been around since someone had a hunch that tele- phone service could take a cue from the railroads and get more use from fewer telephone lines by installing a switching point some- where in the service area. From automatic switch-over when a trans- mission backbone segment fails, to provisioning private lease lines, to telephone service, data communications, audio and video conferen- cing, content creation, distribution, and delivery, modern communi- cations networks simply wouldn't do what they do SO well without it. Switching concepts include circuit switching, cell switching, and packet switching. Transmission is the act of propagating energy or moving informa- tion from point A to point B. In the context of communications PRACTICAL IP AND TELECOM FOR BROADCAST ENGINEERING AND OPERATIONS networking, the term includes sending and receiving. If the heart of the network is the clocking system, transmission is analogous to the arteries and capillaries carrying oxygen from the lungs to the brain and other important organs. Modern communications network transmission seems to have started when someone figured out that a direct current voltage applied to one end of a pair of wires could be detected at the other end as long as the conductive characteristics of the path are intact. Without the underlying transmission faciliti