(Siemens) EDS

Siemens EDS is the type of digital exchange equipment which was used to build the German DATEX-L CSPDN (circuits switched public data network). It was also used as backbone to migrate Telex subscribers away from the older electromechanical switches. Since it didn't just serve one data technology, but (at least) Telex, CSPDN__Datex-L and Teletex, the network based on EDS technology was also called IDN (Integriertes Daten Netz).

EDS is the result of a development collaboration between the two manufacturers Siemens AG and SEL (Standard Elektronik Lorenz AG)

Early design started in 1965 by consultation of Deutsche_Bundespost with the industry, and subsequent testing, the first EDS exchange wnet into production in 1975 in Mannheim. It was supposedly the first world-wide fully electronic circuit-switched data exchange supporting up to 16,000 subscribers via time division multiplex. By 1978, more than 60% of all Telex and Datex subscribers had been migrated over to the EDS.

Technical Data


ESD exchanges had a maximum capacity of 16384 connections. Some of these were needed internally, so the real number of usable subscriber lines was somewhere betwene 10880 and 11500 depending on the type and speed.

The maximum meory capacity of an EDS Exchange is 25614 words of 4 bytes each, i.e. 1048576 bytes. This memory was used both for the operaingsystem and the circuit switching software as well as data. This memory was implemented as (magnegic) core memory.

The program control unit (Programmsteuerungseinheit)had a median runtime of 25ms for each connection signalling. This means that at an average load of 75% it could establish 30 new connections per second. Each exchange could have two (each of them redundant), doubling the capacity.

Power Consumption

A fully equipped EDS exchange with 16384 connections had a power requirement of 80kW at 60V DC plus additional 15kW at 220V AC. This does not inclulde the substantial amount of additional power required for air conditioning

Space requirement

A fully equipped EDS exchange requires about 200 m2 of floor space. However, adding the additional requirements of peipheral units, multiplexers, air conditioninig / ventilation and for operators this increased to 1200 m2 of floor space.

System Configuration


Updated by laforge 10 months ago · 3 revisions

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