 the introduction of X.25 networks. These 2.4 Kbits networks combined leased services to the user at a local network with switched data services withn the network. (See Figure 56.4.) 2.4 Kbits 2.4 Kbits Local 2.4 Kbits Network 2.4 Kbits X.25 SWITCHED COMPUTER SERVICE Figure 56.5 The user of statistical multiplexing PUBLIC X.25 NETWORK Voice services remained within the PSTN, although some interna- tional applications and large corporate networks were developed Figure 56.4 Remote computer access over the X.25 around analogue leased services. This is very true of North America network and the UK. However, private voice networks were separate from data networks and restrictive in their application because of the poor Unfortunately the earlier PTT X.25 services had some drawbacks: network technology and the monopolistic control of the PTT. The arrival of digital networks brought a new ear of communica- 1. Tariffing based on a number of data packets, SO high usage was tions. During the 1960s more progressive PTTs had started to build more expensive than leased services. digital infrastructures to replace the analogue networks and in the 2. Slow speeds, where new modem technology was now offering 1970s this was dramatically accelerated. faster speeds. Digital networks offer benefits to the PTT which caused this 3. Delays across large networks which did not suit SNA networks. accelerated implementation. These included: Nevertheless, X.25 services could be considered as an alternative 1. Better quality. to Wide Area Networking and would have important benefits for 2. More efficient use of the infrastructure. many network business applications. These included a wide connec- 3. Lower cost. tivity capability, unlike leased services the switched capability 4. Higher speeds. enabled a one to many connection rather than a one to one. The 5. The ability to manage the network efficiently. ability to handle protocol conversion in its simplest form, such as different speeds, and a more robust networking service, since it was This 