EWSD (Elektronisches Wählsystem Digital in German, Electronic Digital Switching System/Electronic World Switch Digital in English) is one of the most widely installed telephone exchangesystems in the world. EWSD can work as a local or tandem switch or combined local/tandem, and for landline or mobile phones. It is manufactured by Siemens AG, who claims that EWSD switches performswitching for over 160 million subscriber lines in more than 100 countries.
DeTeWe bought its first EWSD under license in 1985 for remote switching. Bosch built its first EWSD as a local exchange in1986. Deutsche Telekom, formerly Deutsche Bundespost, the largest German telephone company, uses EWSD and System 12 (Alcatel), the former more than the latter.
In 2007, Nokia Corporation and SiemensAG formed the new company Nokia Siemens Networks, and responsibility of further development and shipments of the EWSD system is dependent on this new company.
1 Hardware2 Software
3 Technical data
5 External links
Main subsystems are:
CP (Central Processor)
MB (Message Buffer)
CCNC (Common Channel NetworkControl)
LINE (Analog Line Group)
LTG (Line Trunk Group)
DLU (Digital Line Unit)
SN (Switching Network)
PA (ISDN Primary Access) 
All system units are redundant so theinactive side can take over immediately in case of an error.
DLU handles analog and ISDN lines and includes codecs for analog lines, one of the BORSCHT functions for subscriber lines. Digital signalsare assigned a time slot. DLU concentrates traffic onto a Line B unit, as well as Primary ISDN and V5.2 connections. Supervision and address signaling (dial pulse, DTMF) are also integrated in theDLU. For PCM-30 (E-1) connections to other exchanges, Line C Units are used, which also handle signaling including SS7, MFC R2 signalling, IKZ (dial pulse), and E&M.
The Switching Network consists...