Electronic Switching (ESS)

While our museum focuses mainly on maintaining historic electro-mechanical switching, we do have a few of the electronic based switches that replaced them. In the Central Office, electronic switching dramatically reduced the amount of floor space and in fact the number of floors required for an entire office. However, in many cases a whole new building attached the old central office was required to house the new switching equipment while the old faithfully served the community.

1ESS – Class 5

(currently not on display)

This historic digital switch replaced the Parkway Panel Office in 1972.

3ESS – Class 5

(1976 – 1996)

The Western Electric 3ESS was designed for small communities and can support up to 4500 lines. While not widely deployed, the 3ESS took on the role of the Step By Step Strowger switch in suburban and rural areas as the Community Dial Office (CDO). These

5ESS – Class 4, Class 5

(1982 to the present)

The Western Electric 5ESS is currently manufactured by Alcatel (via Lucent, former Bell Labs). It is a versatile modular switch with software switching generics which can be configured for wired and mobile use. If you have a cellphone, chances are your Call Detail Record (CDR) for phone calls you make are being processed by an ECP in High Capacity Automatic Message Accounting (HCAMA) format.


(1975 to the present)

(Stephen Jones and Bruce Savage of Bell Laboratories 1975 with the Dimension EKTS)

The Electronic Key Telephone System (EKTS) for Electronic Private Automatic Branch eXchange (EPABX) was developed to replace the 1A2 electro-mechanical (KTS) Key Telephone Switch. However, due to its high reliability the KTS can still be found in use in small office to this day. The first of the EKTS was the Dimension. The Dimension was a modular switch that could serve as little as 100 to 2000 telephones. Successors to the Dimension include the System 75 and System 85 (also known as the Definity 85) which supported digital as well as analog line cards.