Class 5 telephone switches
Encyclopedia
A Class 5 telephone switch is a telephone switch or telephone exchange
in the Public Switched Telephone Network
located at the local telephone company's central office, directly serving subscribers. Class 5 switch services include basic dial-tone, calling features, and additional digital and data services to subscribers using the local loop
. Class 5 switches were slower to convert from circuit switching
technologies to time division multiplexing than the other switch classes.
(DDD) American Telephone & Telegraph
divided the various switches in the U.S. Public Switched Telephone Network (PSTN) into a hierarchy containing five levels (or classes).
In modern times only the terms Class 4 and Class 5 are much used, as any tandem office is referred to as a Class 4. This change was prompted in great part by changes in the power of switches and the relative cost of transmission, both of which tended to flatten the switch hierarchy.
; 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 dial tone - they simply route calls between other switches, so they are more concerned with efficient switching and signalling.
Typically a Class 5 switch will cover an area of a city, an individual town, or several villages and could serve from several hundred to 100,000 subscribers.
In the British telephone network, a Class 5 switch is known as Digital Local Exchange (DLE).
Since the replacement in the 1980s and 90s of electromechanical
exchanges by modern digital ones, the function of a Class 5 switch in rural areas is often performed by some form of remote switch
or Remote Digital Terminal
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.
, panel
, and crossbar. 5XB crossbar switches were introduced in large numbers in the 1950s and 60s, and 1ESS
switches and variants in the 1970s and 80s. Most of the above 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 Siemens EWSD
and Ericsson AXE telephone exchange
.
By the turn of the century, US and European service providers have continued to upgrade their networks, replacing DMS-10, DMS-100, 5ESS, GTD-5 and EWSD technology with MetaSwitch Networks, Genband
(Nortel), Sonus and Broadsoft technology.
Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
in the Public Switched Telephone Network
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
located at the local telephone company's central office, directly serving subscribers. Class 5 switch services include basic dial-tone, calling features, and additional digital and data services to subscribers using the local loop
Local loop
In telephony, the local loop is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the carrier or telecommunications service provider's network...
. Class 5 switches were slower to convert from circuit switching
Circuit switching
Circuit switching is a methodology of implementing a telecommunications network in which two network nodes establish a dedicated communications channel through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the...
technologies to time division multiplexing than the other switch classes.
Telephone switch hierarchy
In order to organize Direct Distance DialingDirect distance dialing
Direct distance dialing or direct dial is a telecommunications term for a network-provided service feature in which a call originator may, without operator assistance, call any other user outside the local calling area. DDD requires more digits in the number dialed than are required for calling...
(DDD) American Telephone & Telegraph
American Telephone & Telegraph
AT&T Corp., originally American Telephone and Telegraph Company, is an American telecommunications company that provides voice, video, data, and Internet telecommunications and professional services to businesses, consumers, and government agencies. AT&T is the oldest telecommunications company...
divided the various switches in the U.S. Public Switched Telephone Network (PSTN) into a hierarchy containing five levels (or classes).
- Class 1 exchanges were international gateways - handing off and receiving traffic from outside the USA and Canadian networks.
- Class 2 exchanges were tandem exchanges which interconnected whole regions of the AT&T network.
- Class 3 exchanges were tandem exchanges connecting major population centres within particular region of the AT&T network.
- Class 4Class 4 telephone switchA Class 4, or Tandem, telephone switch is a U.S. telephone company central office telephone exchange used to interconnect local exchange carrier offices for long distance communications in the Public Switched Telephone Network....
exchanges were tandem exchanges connecting the various areas of a city or towns in a region. - Class 5 exchanges were those to which subscribers and end-users telephone lines would connect.
In modern times only the terms Class 4 and Class 5 are much used, as any tandem office is referred to as a Class 4. This change was prompted in great part by changes in the power of switches and the relative cost of transmission, both of which tended to flatten the switch hierarchy.
Function
The fundamental difference between a Class 5 and the other classes of exchange is that a Class 5 switch provides telephone service to customers, and as such is concerned with "subscriber type" activities: generation of dial-tone and other "comfort noises"Comfort noise
Comfort noise is synthetic background noise used in radio and wireless communications to fill the artificial silence in a transmission resulting from voice activity detection or from the audio clarity of modern digital lines....
; 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 dial tone - they simply route calls between other switches, so they are more concerned with efficient switching and signalling.
Typically a Class 5 switch will cover an area of a city, an individual town, or several villages and could serve from several hundred to 100,000 subscribers.
In the British telephone network, a Class 5 switch is known as Digital Local Exchange (DLE).
Since the replacement in the 1980s and 90s of electromechanical
Strowger switch
The Strowger switch, also known as Step-by-Step or SXS, is an early electromechanical telephone switching system invented by Almon Brown Strowger...
exchanges by modern digital ones, the function of a Class 5 switch in rural areas is often performed by some form of remote switch
Distributed switching
Distributed switching is an architecture in which multiple processor-controlled switching units are distributed. There is often a hierarchy of switching elements, with a centralized host switch and with remote switches located close to concentrations of users....
or Remote Digital Terminal
Remote digital terminal
In telecommunications, a Remote Digital Terminal typically accepts E1, T1 or OC-3 digital lines to communicate with a telephone Access network or telephone exchange on one side, and forms a Local Exchange on the other, which is connected to Plain Old Telephone Service lines....
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
When the office classification system for DDD was set up, the principal designs in use for Class 5 in the USA were step by stepStrowger switch
The Strowger switch, also known as Step-by-Step or SXS, is an early electromechanical telephone switching system invented by Almon Brown Strowger...
, panel
Panel switch
The panel switching system was an early type of automatic telephone exchange, first put into urban service by the Bell System in the 1920s and removed during the 1970s...
, and crossbar. 5XB crossbar switches were introduced in large numbers in the 1950s and 60s, and 1ESS
1ESS switch
The Number One Electronic Switching System, the first large-scale Stored Program Control telephone exchange or Electronic Switching System in the Bell System, was introduced in Succasunna, New Jersey, in May 1965. The switching fabric was composed of reed matrixes controlled by wire spring relays...
switches and variants in the 1970s and 80s. Most of the above were removed in the late 20th Century, primarily replaced in North America by DMS-10, DMS-100
Digital Multiplex System
Digital Multiplex System is the name shared among several different telephony product lines from Nortel Networks for wireline and wireless operators...
and 5ESS
5ESS Switch
The 5ESS Switch is a Class 5 telephone electronic switching system sold by Alcatel-Lucent. This digital central office telephone circuit switching system is used by many telecommunications service providers.-History:...
switches in the Bell operating territories and the GTD-5 EAX
GTD-5 EAX
The GTD-5 EAX is the Class 5 telephone switch developed by GTE Automatic Electric Laboratories...
in the GTE operating areas. Principal European products include Siemens EWSD
EWSD
EWSD is one of the most widely installed telephone exchange systems in the world. EWSD can work as a local or tandem switch or combined local/tandem, and for landline or mobile phones...
and Ericsson AXE telephone exchange
AXE telephone exchange
The AXE telephone exchange is a product line of circuit switched digital telephone exchanges manufactured by Ericsson, a Swedish telecom company. It was developed in 1974 by Ellemtel, a research and development subsidiary of Ericsson and Televerket.. The first system was deployed in 1976...
.
By the turn of the century, US and European service providers have continued to upgrade their networks, replacing DMS-10, DMS-100, 5ESS, GTD-5 and EWSD technology with MetaSwitch Networks, Genband
Genband
GENBAND is a privately held company which makes IP multimedia application and infrastructure products and solutions for fixed wire line, mobile, and cable network service providers. The company was formed in 1999 as General Bandwidth and since 2010 is headquartered in Frisco, Texas.It has major...
(Nortel), Sonus and Broadsoft technology.