External line access cct. - allows calls to be dialled directly even when all internal junctions are busy

摘要

A system for the improvement of direct access to an external line from a small local telephone exchange is presented. The external line can be directly dialled through the exchange by using a particular number or sequence of numbers, but if all the local junctions are busy, an "engaged" signal will result even though the external line is free. The system presented here incorporates an AND gate which detects the fact that all the local junctions are used, and activates a relay which allows the subscriber direct access to the coupling unit on to the external line without the usual process of decoding the external code like an internal one. The coupling is also affected by the relay so that the code for the outside call is directly transmitted.