{{No footnotes, date=August 2008 A class-5 telephone switch is a

telephone exchange A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syst ...

in the

public switched telephone network The public switched telephone network (PSTN) provides Communications infrastructure, infrastructure and services for public Telecommunications, telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that ...

(PSTN) that directly serves

subscriber The subscription business model is a business model in which a customer must pay a recurring price at regular intervals for access to a product or service. The model was pioneered by publishers of books and periodicals in the 17th century, and ...

s and manages subscriber calling features. Class-5 services include basic

dial-tone A dial tone is a telephony signal sent by a telephone exchange or private branch exchange (PBX) to a terminating device, such as a telephone, when an off-hook condition is detected. It indicates that the exchange is working and is ready to initia ...

, calling features, and additional digital and data services to subscribers connected to a local loop.

Function

A class 5 switch provides telephone service to end customers locally in the exchange area, and thus it is concerned with "subscriber type" activities: generation of dial-tone and other " comfort noises"; handling of network services such as advice of duration and charge etc. Specifically, a class-5 switch provides dial tone, local switching and access to the rest of the network. Class-4 switches do not provide subscriber lines, their role is to route calls between other switches. Typically a class-5 switch serves an area of a city, an individual town, or several villages and could serve from several hundred to 100,000 subscribers. Since the replacement of electromechanical exchanges by modern digital ones, the function of a class-5 switch in rural areas is often performed by a remote switch or

Remote Digital Terminal In telecommunications, a remote digital terminal (RDT) typically accepts E1, T1 or OC-3 digital lines to communicate with a telephone Access network (AN) or telephone exchange (Local Digital Switch, LDS) on one side, and forms a local exchang ...

installed at the original switch site to handle local switching or concentration, respectively. The class-5 switching infrastructure is then physically located in a larger population center. Urban areas with extensive underground plant tend to keep the classic class-5 office architecture.

Hardware

Before the office classification system for Direct Distance Dialing (DDD) was established, the principal designs in use for class 5 in the US were crossbar systems, Panel switches, and Strowger-type step-by-step systems. The DDD program involved installations of large numbers of new 5XB crossbar switches in the 1950s and 1960s. In addition,

1ESS switch The Number One Electronic Switching System (1ESS) was the first large-scale stored program control (SPC) telephone exchange or electronic switching system in the Bell System. It was manufactured by Western Electric and first placed into servi ...

es and their variants appeared in the 1960s. Most of these systems were removed in the late 20th century, primarily replaced in North America by DMS-10, DMS-100 and 5ESS switches in the Bell operating territories and the GTD-5 EAX in the GTE operating areas. Principal European products include Ericsson AXE telephone exchange, Siemens EWSD and Alcatel-Lucent S12 and E10. In the 21st century, US and European service providers continued to upgrade their networks, replacing older DMS-10, DMS-100, 5ESS, GTD-5 and EWSD switches with Voice over IP technology.

Function

Hardware

See also