It’s helpful for data communication and IT students to understand the evolution of Data communication systems. The first phase in the evolution of data communication systems was Telegraph Systems. Later, with developments in the telephone systems, it was then possible to interconnect various computer terminals for data communication. With the advancements in network computing and the digitization of computer networks, it was now possible to setup an efficient data communication network within each region and connecting such network with the world-wide network.
Commercial data transmission was started with a leased telephone line established as early as 1940s. Later PSTNs (Public switched telephone network) was established which is basically dial up service. The speed pf leased lines and PSTNs were later greatly improved to cope up with changing needs and advancements in network computing. Leased line services were expensive and were not able to support multiple speeds and protocols interworking. The dial-up services, on the other hand, had the problem of long setup time, lower speed. This was further improved by the introduction of line conditioning equipment, local digital data networks, and premium data services.
The inherent setup, speed, and maintenance problems were further improved by the introduction of packet-switched data networks (PSDN). PSDNs could support speeds upto 64 Kbps for intercity communications. Satellite-based data networks usually called Remote area business message networks (RABMN) were also introduced in some countries which when connected to the PSDN provided world-wide data communication. Such data communications are still standard form for providing Internet services in some countries.
With the developments in mobile communication and radio communications, facilities such as cell phones, pager services etc evolved. Developments in ISDN (Integrated services digital network) led to integrated voice and data services including video, graphics and sound via PSTN.