Communication networks are made up of transmission lines, concentrators, switching mechanisms and non-data processing components. Due to increased competition in the communication industry, new and specialised common carriers and value-added networks with data processing equipment, is also linked to communication networks. The current technological trend setter in communications is "packet switching technology". The greatest advantage of packet switched networks is in applications where the distance involved is great. Information services involve relatively large quantities of data for full bibliographic or full text retrieval, and therefore, the distance advantage applies more clearly to these applications. Depending upon the area of administrative jurisdiction, networks fall into three categories: Local Area Networks (LANs), Metropolitan Area Networks and Wide Area Networks (WANs).
Local Area Networks (LANs):
A Local Area Network connects a large number of different types of equipment, including computer terminals, fax, telex, CD ROM players, etc., on a single site. The majority of LANs use packet switching technology and offer very high transmission speeds - up to one hundred times faster than those available on public networks at present. Most of these are baseband that is they carry only digital computer data, but broadband LANs can carry video and voice signals as well as data. The topology of LANs can vary greatly (i.e., linear, star, ring) affecting efficiency, reliability and costs.