A Frequency-Division Multiplex Key Telephone System
G. Aaronson, Anthony S. Acampora · IEEE Transactions on Communication Technology · 1971
A new key telephone system, which uses four-wire connections between the telephone stations and the electronic key service unit, is described. The drastic reduction in the number of conductors results from the transfer of logic functions from the telephone stations to a central controller. Supervision and control signals are provided by a frequency division multiplex arrangement.