mmon examples of leased-line connections. The leased line is connected all the time, but dial-up or switched lines are Data Communications Short-haul leased line connection Telecommunications Router or network Router or switch terminal 4-wire physical terminal switch circuit or two optical fibers Long distance leased line circuit: Telecommunications network Router or Digital Digital Router or switch terminal multiplexer Point-to-point multiplexer terminal switch transmission Local access network up to 10 Gbps Figure 6.24 Regional and long-distance leased lines. connected only on demand. However, the switched line requires higher investments in the network equipment and the fee is higher if the circuit is connected most of the time. In LAN interconnections the required capacity is often high and the connection is needed SO frequently that the leased line often provides better service with a lower service cost in a regional corporate network. Another advantage of leased lines is high security because leaves- dropping requires physical access to the dedicated channel. Packet-switched alternatives are also available for long-distance inter- connections. These are WANs and they use frame relay, ATM, or IP tech- nology (see Sections 6.6, 6.7, and 6.8). They are often economically attractive because the core network costs are shared among many customers of the network operator. 6.5 LANs The data communications systems that we described previously rely on the services provided by a public telecommunications network operator. How- ever, there is a need for high-data-rate communications inside a building or a company; to satisfy these needs, local data communications networks, called LANs are built. Introduction to Telecommunications Network Engineering 6.5.1 LAN Technologies and Network Topologies LANs provide high-data-rate communications between computers, for example, inside one building. Because of the high transmission capacity (10 Mbps or higher) only short distances are allowed. The typical maximum transmission dis