Small key telephone system

摘要

An intercommunication system makes use of existing quad wiring to provide intercom communication between the subsets of the system, as well as communication with a standard central office, or an "outside line". Each subset is provided with a control sequencer for selectively connecting the set to either an "intercom" or an "outside" or C.O. line. When the handset of a subset is lifted off the respective hookswitch, the subset is automatically connected to intercom line and signalling between subsets can occur with the outside line on "hold". The hold is released automatically when another handset is picked up. Two indicators show activity on the two lines respectively.