gh capacity submarine systems are put into use every year. In addition to speech, submarine systems carry intercontinen- tal Internet traffic, which is estimated to take most of the capacity of the new systems under installation. Submarine systems are the main paths for inter- continental telephone calls and Internet communication. Satellite systems are sometimes used as backup systems in the case of congestion. We described the common structure of the global telecommunications network without separating the different network technologies. We need dif- ferent network technologies to provide different types of services, and the telecommunications network is actually a set of networks, each of them hav- ing characteristics suitable for the service it provides. In the next section we The Telecommunications Network: An Overview Telecommunication Earth satellite station Subscriber A Earth station National network Submarine cable system Third country International switching center network High capacity National PSTN optical line system Subscriber B Figure 2.17 The international network. describe briefly the most important network technologies, some of which are discussed in more detail in later chapters. 2.10 Telecommunications Networks Up to this point, we have explained the operation of the public switched tele- communications network and used the conventional telephone networks as an example. However, the public network contains many other networks that are optimized to provide services with different characteristics. We review these different network technologies in this section. We can divide telecommunications networks into categories in any of many different ways. If we consider the customers of networks and the avail- ability of services, there are two broad categories: public networks and private or dedicated networks. 2.10.1 Public Networks Public networks are owned and managed by telecommunications network operators. These network operators have a license to provide telecommunica- tions services and that is 