ing Earth station to the receiving Earth station. The speaker has to wait for a response for approximately 0.5 seconds and this disturbs an interactive communication. Introduction to Telecommunications Network Engineering Most telecommunication Uplink satellites are placed in microwave the geostationary orbit. radio signal Downlink at 6 GHz band They are used to provide telecommunication services microwave for ships and aircrafts, radio signal at 4 GHz TV broadcasting, and Approximately mobile telephone and 36,000 km data services. Earth Earth station station Delay from Earth station to Earth station is about 250 ms Figure 4.31 Satellite transmission. However, satellite systems can provide telephone service to areas where no terrestrial infrastructure for telecommunications exists. To provide wide coverage and smaller delay in mobile telephone serv- ice, many lower orbit satellite telephone systems have been developed and put into use. They have not been successful because public land mobile systems (PLMNs), such as GSM and CDMA, have grown rapidly and taken the major share of mobile telephone business. One major application for satellite communications has been broadcast satellite TV. A TV program from a single satellite may be received in any part of a continent simultaneously making distribution cost per customer low. Satellite systems may also provide an attractive solution for data communica- tions, for example, for a global hotel chain that needs a global data service to keep reservation databases synchronized. 4.8 Transmission Equipment in the Network Many different systems are needed in the telecommunications network to transmit signals via various different channels. We review the most common transmission devices or systems in this section. Some of them were already discussed in the previous section, and some of them are also shown in Figure 4.32. Transmission Chain configuration of a transmission system Ring topology TM = Terminal multiplexer Modems convert digital signal into an analog form. Add/drop M