sentences:  In the 1960s, Northern Electric developed the SA-1 community dial office as a small Class 5 crossbar switch for local use in rural areas.In the late 1970s, Western Electric's number 3 Electronic Switching System (ESS) was installed in small communities with up to 4500 telephone lines; it also served as workhorse in some large private branch exchange installations.Late in the 20th century the smallest offices were replaced by remote concentrators connected to a host office in an adjacent exchange area, which may be several miles away.