EWSD is a product name for electronic telephone switching systems of Siemens AG ( now Nokia Solutions and Networks). The name is due to the abbreviation of the words electronic voting system Digital.

Area of ​​application

Exchanges of type EWSD for public telephone networks, as switching equipment of other manufacturers, either as a local exchange, as a remote switching office, or a combination of both are supplied. There are different variants for fixed and mobile networks. Customers of EWSD switching systems are, for example, Telecommunications companies such as the German Telekom, M-net, Versatel, Colt Technology Services, QSC, Telekom Austria, Vodafone or dtms. Other companies use systems from other manufacturers. Siemens admits to have sold EWSD systems in over 120 countries.


The system was developed by Siemens AG. It was the second generation of electronic dialing systems from Siemens after the system EESC (electronic voting system analog ). Companies like Bosch DeTeWe and fitted the system under license. The first EWSD system from Siemens in 1980 put into operation in Hamburg, where they replaced the analog switching method used until then. From DeTeWe the first EWSD was taken to the remote switch into operation in 1985, a year later, the first built by DeTeWe digital local exchange. DeTeWe PCN realized switching network nodes at over 180 locations. The German Telekom uses EWSD from Siemens and Alcatel System 12. The proportion of EWSD systems outweighs that of the system 12 own hardware manufacturing was discontinued in 2003 and the EWSD division was disbanded on 31 December 2005. The system " EWSD " at the time was the world's best-selling fixed-line switching system. However, Siemens has not managed to jump into the internet age, the plants were too big, too expensive in comparison to the growing competition such as CISCO or other, Asian competitors and had a much higher power consumption.


The modules are inserted vertically into shelf, the rear wall makes the electrical connections between them. Several shelf on top of each housed in a rack, which is closed as a cabinet with doors on the front and back. The modules are accessible from the front, cables are connected to the rear. In the top level of a frame series is the safety rail. At the lowest level there are fans that provide air circulation in the cabinet. Thus, the waste heat of the modules is derived. A EWSD system can consist of several cabinets, which is called a frame number. The cables can be fed through a grid of the area of ​​the room ceiling or a false floor.


The main components of a EWSD system

  • CP ( Central Processor or Coordination Processor)
  • MB (Message Buffer )
  • Replaced CCNC ( Common Channel Network Control ), in newer switches by SSNC (Signaling System Network Control)
  • LTG ( Line Trunk Group )
  • (DLU Digital Line Unit)
  • SN (Switching Network, coupling field )

All key system units are configured redundantly. So can take over the operation immediately in case of an error that does not mediating page.

The connection part DLU takes the analog and ISDN subscriber lines and converts among others the analog signals into digital signals (one of the BORSCHT functions of a subscriber line interface circuit ). The digital signals are assigned to a channel of a PCM system. Digital connection cables, for example, an ISDN basic access will be directly assigned to a PCM channel. In the DLU of the traffic is concentrated and transferred to the LTG type B. Add to that the inclusion of PCM30 systems, such as primary rate interfaces or V5.2 controlled access networks. Their connection to the switching network is also carried on LTG type B. Other functions for controlling the connection, such as generating the ringing voltage and recording the dial information ( pulse dialing, tone dialing ) are integrated in the DLU. The connection part is controlled by the group processor. DLU can be operated in remote peripheral units ( APE). For the connection via PCM30 to other exchanges LTG Type C will be used. There also the signaling of these compounds is terminated. Different signaling systems can be used, for example, SS7, MFC R2, TSC, E & M. The switching network consists of space switch with 4 space switching matrices, 16/ 16 (16 inputs and 16 outputs ) as well as a time switching stage 16 time switching matrices with 4 outputs and inputs (4 /4). In the time switching stage takes place, the spatial and temporal transposition of the channels. The controller takes over the coordination processor CP.

The following types of coordination processors there are:

  • CP 103 with max. 22,000 call attempts in the busy hour
  • CP 112 with max. 60,000 call attempts in the busy hour
  • CP 113D with up to one million call attempts in the busy hour
  • CP 113C with up to six million call attempts in the busy hour (C for Compact)
  • CP 113E with up to ten million call attempts in the busy hour


The software of the EWSD is called APS (Application Program System). The GSP is on a hard drive and is a private, Siemens involving Bosch developed specifically for EWSD plants operating system. It is programmed primarily in the programming language CHILL. The user software is specifically mediation and serves, among other traffic control, route search and acquisition fees. The support software is used to generate data, translating programs, binding of modules as well as for management of libraries. The operational and data communication software is used for the Cooperation of maintenance centers and switching centers.


  • Number of subscriber lines to 250,000
  • Number of connection lines 240,000
  • Feed through traffic 25,200 Erlang
  • Connection attempts in the busy hour 10 million
  • Operating voltages 48 V - 60 V - 90 V -
  • Zoning ( charging zones ) 127 zones, each zone 6 Rates
  • Tariff switching at 15- minute intervals
  • Space at 10,000 subscriber lines 35 m²