Editing Remote concentrator (section)

== Operation ==
When a user picks up their phone, the concentrator produces the [[dial tone]].  When the user dials, it reads the tones.  Once the user has completed dialing, the concentrator's microcomputer sends the dialing data to the central switch, which allocates a time slot for the dialing phone on the wire pairs that pass through the concentrator and through the switch. 

After the central switch tells the concentrator which time slot to use, the concentrator "opens" a time-slot on the loop to a local phone.  The allocated time slot on the wiring into the concentrator is used to send data from the remote telephone's microphone to the local telephone's speaker.  The allocated time slot on the wiring out of the concentrator (with the same time slot number) carries data from the local microphone to the remote speaker.

To arrange a connection, the switch just completes the circle between the user's phone and the remote phone.  It interchanges the data from one to the other.  In this limited sense, telephone "exchange" is exactly correct terminology.