plifiers and vice versa. The line layer includes all the components in the media layer, plus light wave terminal equipment at each end of the facility. The function of these units is to convert electrical signals to light wave signals. They also act as an add/drop multiplex unit whereby one or more STS can be broken out of the backbone and used to originate and terminate traffic from both sides. Another way to view the LTE is to say that they accumulate and map STS signals and multiplex them into a backbone signal. On the other side, or in the form of a reverse function, they break out STS signals and pass them to terminal multiplexing TM or add/drop connections in the The terminal multiplexing equipment builds up and breaks out STS signals. Another way of saying this is that the TM aggregates traffic from legacy digital sources such as those that originate in voice grade circuit switching and cross-connect equipment. It also accommodates STS-1 or 51.8 Mbs streams as a peer to legacy T1, E1, E3, and DS3 traffic streams. Other non-PDH layer 2 traffic can also be accommo- dated such as ATM, asynchronous, unchannelized, E3, DS3, and packet-over SONET or point-to-point protocol on high level data link control (PPP/HDLC). There are other important functions involving monitoring, alarms, network performance, and network management, including support for OAMP. PRACTICAL IP AND TELECOM FOR BROADCAST ENGINEERING AND OPERATIONS Media layer components consist of fiber conductors, regenerators, light wave amplifiers, conduit, poles, and other supporting and pro- tection infrastructure objects. SUMMARY In summary, transmission systems have evolved over time beginning with basic or baseband electrical transmission. As electronics evolved, radio or wireless transmission evolved and served commu- nications growth very well. Just when it seemed like the radio spec- trum was becoming congested and in need of capacity, satellite technology provided much needed relief and new ways of serving the broadcast industry as well as competi