The Elektronisches Wählsystem Digital (EWSD), translated to ''Electronic Digital Switching System'' in English, is a widely installed German

telephone exchange A telephone exchange, telephone switch, or central office is a central component of a telecommunications system in the public switched telephone network (PSTN) or in large enterprises. It facilitates the establishment of communication circuits ...

system, originally introduced in 1975 by

Siemens AG Siemens AG ( ) is a German multinational technology conglomerate. It is focused on industrial automation, building automation, rail transport and health technology. Siemens is the largest engineering company in Europe, and holds the posit ...

, but discontinued in 2017. EWSD can operate as a local end-office switch, a tandem switch, or in a combined configuration for

landline A landline is a physical telephone connection that uses metal wires or optical fiber from the subscriber's premises to the network, allowing multiple phones to operate simultaneously on the same phone number. It is also referred to as plain old ...

or mobile telephone service. Siemens claims that EWSD switches perform switching for over 160 million subscriber lines in more than one hundred countries.

History

EWSD was introduced in 1975 as a successor of the EWSA (''Elektronisches Wählsystem Analog''), which was using analogue technology. DeTeWe bought its first EWSD under license in 1985 for remote switching. Bosch built its first EWSD as a local exchange in 1986.

Deutsche Telekom Deutsche Telekom AG (, ; often just Telekom, DTAG or DT; stylised as ·T·) is a partially state-owned German telecommunications company headquartered in Bonn and the largest telecommunications provider in Europe by revenue. It was formed in 199 ...

, formerly Deutsche Bundespost, the largest German telephone company, uses EWSD and System 12 (Alcatel), the former more than the latter. In 2007, Siemens AG and

Nokia Nokia Corporation is a Finnish multinational corporation, multinational telecommunications industry, telecommunications, technology company, information technology, and consumer electronics corporation, originally established as a pulp mill in 1 ...

Corporation jointly formed a new company called ''Nokia Siemens Networks'', and transferred responsibility of further development and shipments of the EWSD system to the new company. In 2013, after Nokia completed the acquisition of the Siemens stake in the company, Nokia Siemens Networks was rebranded to ''Nokia Solutions and Networks'', and finally as

Nokia Networks Nokia Networks (formerly Nokia Solutions and Networks (NSN) and Nokia Siemens Networks (NSN)) is a Finnish multinational corporation, multinational data networking and telecommunications equipment company headquartered in Espoo, Finland, and who ...

in 2014.

Hardware

The major six subsystems of EWSD are the Coordination Processor (CP), the Common Channel Network Control (CCNC), the Line Trunk Group (LTG), the Digital Line Unit (DLU), the Switching Network (SN), and the ISDN Primary Access Unit (PH).http://www.melachroinakes.de/pdf/SMC.pdf All system units are redundant so that the inactive side of each component can take over immediately in case of an error. DLU handles analog and

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. ...

lines and includes codecs for analog lines, one of the ''

BORSCHT Borscht () is a sour soup, made with meat stock, vegetables and seasonings, common in Eastern Europe and Northern Asia. In English, the word ''borscht'' is most often associated with the soup's variant of Ukrainian origin, made with red b ...

'' functions for subscriber lines. Digital signals are assigned a time slot. DLU concentrates traffic onto an LTG-B unit, as well as Primary Rate ISDN and V5.2 connections. Supervision and address signalling (dial pulse,

DTMF Dual-tone multi-frequency (DTMF) signaling is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed ...

) are also integrated in the DLU. For PCM30 (E-1) connections to other exchanges, LTG-C Units are used, which also handle signalling including SS7, MFC

R2 signalling Signalling System R2 is a signalling protocol for telecommunications that was in use from the 1960s mostly in Europe, and later also in Latin America, Asia, and Australia, to convey exchange information between two telephone switching systems for es ...

, IKZ (dial pulse), and E&M. The Switching Network consists of four space division stages of 16x16 switches, and a time division section with 16 stages of 4x4 switches. Control is provided by the Coordination Processor. The Coordination Processors exists in several types: * CP103 with max 22,000 BHCA ( Busy Hour Call Attempts) * CP112 with max 60,000 BHCA * CP113D with max one million BHCA * CP113C with max six million BHCA * CP113E with max ten million BHCA

Software

The software of EWSD is called the Automatic Program System (APS). The APS is stored on a disk drive and includes the operating system, developed by Siemens in cooperation with Bosch. It is predominantly written in the

CHILL In computing, CHILL (an acronym for CCITT High Level Language) is a procedural programming language designed for use in telecommunication switches (the hardware used inside telephone exchanges). The language is still used for legacy systems ...

language. Application software is switch-specific and manages functionality including traffic management, path search, and call charging. Support software serves translating programs, binding modules as well as administration of libraries for generating data. Operating and data

communication software Communication software is used to provide remote access to systems and exchange files and messages in text, audio and/or video formats between different computers or User (computing), users. This includes terminal emulators, file transfer programs, ...

serve for co-operation of maintenance centers and switching centers.

Technical data

* Number of access lines: to 250,000 * Number of feeder lines: 240,000 * Traffic connection: 25,200 * Call attempts in busy hour: 10 million * Operating voltages: -48V -60V -90V * Rate zones: 127, for each zone of 6 tariffs * Tariff change-over at 15-minute intervals * Space requirement with 10,000 access lines: 35 square meters

References

External links

Osmocom Retronetworking Wiki - EWSD
{{Telephone Switches Telephone exchange equipment Siemens products