Abstract

Introduction to Data
Communications

Samuel F.B. Morse invented the first data communication device, the telegraph, in 1844. The telegraph and its successor the teletypewriter played an important role in communications for the first century of their existence. These devices were the principal means of sending messages over long distances until computers appeared. Computers began as text-based systems that used punched cards for input and magnetic tape for storage.
Computer ports could easily be extended to distant terminals with a modem running over a telephone circuit. Remote printers, successors to the teletypewriter, had printing speeds in the order of 100 words per minute, more than the speed of most typists. One hundred wpm is only about 80 bps, and a telephone circuit supports 2400 bps with the simplest of modems. It was not cost-effective to use a fraction of the capacity of a voice circuit for a single
VDT. Moreover, 1 bit in error could render a message stream unusable.

The earliest LANs were in the order of 1 Mbps, but these soon increased to 10 and 100 Mbps. As organizations interconnected their LANs and distributed information over wide areas, the bandwidth of an analog circuit became a severe choke point. Users, having no idea where information was stored, noted the vast difference in response time between a local file delivered over a high-speed LAN and one delivered over a voice-grade wide area network (WAN).
Fiber optics was in its infancy in 1980 and long-haul circuits were transported over analog microwave radio. Digital microwave was available, but its error rate limited it to a span of about 500 miles (800 km). The restrictions of the analog voice network remained until fiber optics relieved the bottleneck. Another major change in computer applications was the transition from textbased information to graphics. Computers had been migrating toward graphics for several years, but the Web accelerated the change.
Multiplexers have largely been supplanted by devices that interconnect LANs, and the older data networks have evolved into networks of interconnected LANs.