Toll restrictor for a time division telecommunication system

The design of a toll restrictor, used in a time division multiplexed telephone switching system is presented in this thesis.

The schemes most commonly employed for toll restrictor design were capable of providing only limited digit analysis and contributed significantly to the high overall system cost.

The design presented herein provides the TD-100 private automatic branch exchange with a toll restrictor not only very economical, flexible, and reliable, but also capable of simultaneously monitoring up to 60 outward dialed calls and analyzing a maximum of 7 digits per call.

Its flexibility and the approach employed have been quite unique (United States Patent 24,046,965, September 6, 1977). The design requirements, as well as additional features, were fulfilled by use of microprogramming techniques, linked together with various types of small, medium, and large scale digital integrated circuits.