These lines could be terminated with phone sets or teletypewriters. This setup is attractive in two ways. First, commu- nication takes place in real time, allowing a dialogue, where desir- able, between the stations. Second, any station can communicate with 94 TELECOMMUNICATIONS Message Circuit (line) Leased line switching switching network network network Fig. 6-8. Communications network configuration alternatives. any other station at any time and there will never be a "busy" when trying to deliver a message. As the number of sites increases, how- ever, the number of required lines increases geometrically to the point that leased line cost quickly becomes prohibitive. Circuit switching is much more economical in line use. In this method, a line is placed between each site and some central station. Therefore, for n stations only n lines are needed. Connections are then made by command at the central station to allow communi- cations between sites. Like leased line networks, all communication takes place in real-time. A connection, however, is not always pos- sible since there is only one link from the central station to each site. In message switching, the problem of "busies" encountered in cir- cuit switching networks is eliminated, since traffic is simply sent to the central site and captured there. The switch will then hold the traffic until the destination leg is able to receive it and will then for- ward the message (Fig. 6-9). The only feature lost is the real-time connection allowing conversational communication. However, this is infrequently used in data communications and its lack is generally not a serious drawback. This is especially true in international com- munications since the originator and recipient of a message are sel- dom working at the same time due to the time-zone differences. Line costs can be reduced even further than for circuit switching net- works. This is because traffic loads can be distributed over a longer period of time. Peaks in traffic are buffered at the switch and sent out s