WSDFrom Wikipedia, the free encyclopediaEWSD(ElektronischesWhlsystemDigitalinGerman, Electronic Digital Switching System/Electronic World Switch Digital[1]inEnglish) is one of the most widely installedtelephone exchangesystems in the world. EWSD can work as a local or tandem switch or combined local/tandem, and forlandlineor mobile phones. It is manufactured bySiemens AG, who claims that EWSD switches perform switching for over 160 million subscriber lines in more than 100 countries.DeTeWebought its first EWSD under license in 1985 for remote switching.Boschbuilt its first EWSD as a local exchange in 1986.Deutsche Telekom, formerly Deutsche Bundespost, the largest German telephone company, uses EWSD and System 12 (Alcatel), the former more than the latter.In 2007,NokiaCorporation and Siemens AG formed the new companyNokia Siemens Networks, and responsibility of further development and shipments of the EWSD system is dependent on this new company.Contents[hide] 1History 2Hardware 3Software 4Technical data 5References 6External linksHistory[edit]EWSD was introduced in 1975 as a sequel of theElektronischesWhlsystem (Analog), which was using analogue technology only.Hardware[edit]Main subsystems are: CP (Central Processor) MB (Message Buffer) CCNC (Common Channel Network Control) LINE (Analog Line Group) LTG (Line Trunk Group) DLU (Digital Line Unit) SN (Switching Network) PA (ISDN Primary Access)[2] PDC (Primary Digital Carrier)All system units are redundant so the inactive side can take over immediately in case of an error.DLU handles analog andISDNlines and includes codecs for analog lines, one of theBORSCHTfunctions for subscriber lines. Digital signals are assigned a time slot. DLU concentrates traffic onto a Line B unit, as well as Primary ISDN andV5.2connections. Supervision and address signaling (dial pulse,DTMF) are also integrated in the DLU. ForPCM30(E-1) connections to other exchanges, Line C Units are used, which also handle signaling includingSS7, MFCR2 signalling,IKZ(dial pulse), andE&M.The Switching Network consists of 4 space division stages of 16x16 switches, and a time division section with 16 stages of 4x4 switches. Control is provided by the CP Co-ordination Processor.There are the following kinds of Co-ordination Processors: CP103 with max 22,000call attempts in the busy hour CP112 with max 60,000 call attempts in the busy hour CP113D with max one million call attempts in the busy hour CP113C with max six million call attempts in the busy hour CP113E with max ten million call attempts in the busy hourSoftware[edit]The software of EWSD is called APS (Automatic Program System). The APS is on a hard drive and includes the operating system, developed by Siemens in cooperation with Bosch. It is predominantly written in theCHILLlanguage. Application software is switch specific and serves among other things 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 datacommunication softwareserve for co-operation of maintenance centers and switching centers.Technical data[edit] 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 metersReferences[edit]1. Jump up^Telephone World - Other Modern Switching Systems of Note