This chapter discussed different types of private network. Private network is that it is primarily intended to carry internal traffic originated by, and destined for, employees of the organisation it exists to serve. Most private networks also have access to public telephone and data services. These networks range in size from those which provide service to a single site to those which link many sites nationwide or even internationally. A small PBX and its extensions and private telephone network are example of a single-site private network in its simplest form; by contrast, a multisite private network may consist of many interlinked switching centres, carrying both speech and data traffic. Two unique network configurations have been developed to permit limited distance direct communication between any two stations without the need for a switching centre. Both employ (a) a common transmission path and (b) a form of distributed packet switching to route messages to the required station. The transmission path is cabled throughout the area to be served so that additional stations (up to a limit of, typically, around 100 stations per network) can be 'plugged in' to it wherever the need arises. Data networks of this type are known by the generic term local area network (LAN) since they are designed specifically for a single site or several nearby sites, where the distances over which data needs to be transmitted are normally quite short and rarely more than a few kilometres. LANs provide for high rates of error-free data transfer and are ideally suited to a general-purpose data network which includes shared-access computers, printers, etc. Given that both LANs and PBXs will be able to offer comparable standards of service integration, the choice between them will have to be made on factors which result from their differing network concepts; the LAN with its distributed switching and ring or bus network, and the PBX with its centralised switching and star network. Technically there would appear to be little to choose between the two systems, and it is not yet possible to predict which might offer the most economic solution. An installed cabling base might well prove to be the deciding factor by determining the network structure and thus the system choice.

Inspec keywords: local area networks; packet switching; private telephone exchanges; telecommunication traffic

Other keywords: data traffic; shared-access computers; distributed packet switching; small PBX; data services; star network; single-site private network; printers; transmission path; multisite private network; general-purpose data network; error-free data transfer; local area network; interlinked switching centres; centralised switching network; public telephone; private telephone network

Subjects: Switching centres and equipment