Retronetworking

h1. Siemens EWSD

Siemens EWSD (Elektronisches Wählsystem Digital) was a family of digital telephone switch (exchange) which was used by more than 300 telephone operators in more than 100 countries world-wide, serving more than 170 million subscriber lines in 1998.

According to Siemens, there were more than 1600 engineers involved in EWSD software development in Munich alone, creating more than 45 million lines of code.

EWSD was not only used for analog and ISDN telephony, but also as FuVSt (radio exchange) for the German C-Netz analog cellphone system, as well as as MSC (Mobile Switching Centre) for digital GSM cellular networks.

To our knowlege, there is currently no communications museum on the planet that has a working EWSD exchange in their collection.  This is hard to believe, given the incredible significance of this equipment for the world-wide telecommunications of the 1980s and 1990s.

h2. EWSDs at private collectors; interconnect to OCTOI

Luckily, there are some private collectors trying to fill that gap:  Jan Pesak in Brno/CZ has one EWSD in operation, and @jolly (long time Osmocom developer) has also managed to "document, tear-down, transport and re-build one at his home in 2023":https://discourse.osmocom.org/t/die-rettung-der-ewsd/30.  We published  "a number of timelapse videos of the dis-assembly  and re-assembly in this playlist":https://tube.tchncs.de/w/p/gNqUfNfRHEd1LXQp97cCej

In November 2023, we "established the first SS7/ISUP interconnect":https://discourse.osmocom.org/t/the-first-ss7-isup-interconnect-at-octoi/204 between the EWSD in Brno/CZ and our [[octoi:|OCTOI]] community ISDN-over-IP network.

h2. Documentation / Hacks

There is tons of original official Siemens documentation for EWSD floating around, as are some training course materials.  We'd like to add some additional bits and pieces here, based on our experience.

Furthermore, we'd also like to create a visual documentation with high-res photographs of each and every circuit board type, EPROM images, etc.  Stay tuned.

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