PURPOSE: To offer easily the same services as a general extension by a simple switching system by calling two-party extension subscribers by making a connection between output signal lines of general calling signal trunks by replacing.
CONSTITUTION: In general, extension calling signal trunks 11 and 14 send a calling signal to an a'-line side between their output signal lines a' and b', so when trunk 11 is connected to two-party subscriber's line 18, only calling bell 16a is put into operation to call only party A. On the other hand, trunk 14 has output signals a' and b' connected reversely by main distributing board 13 by replacing, and consequently when subscriber's line 18 connects to trunk 14 for calling, only bell 17a is put to work to call only party B. To make a two-party mutual call, connecting two-party trunk 12 to subscriber's line 18 calls both parties A and B at the same time. Consequently, the same services as a general extension can easily be offered.
MARUKO AKIHIKO
TANAKA YOSHIHIDE
YOSHIMATSU TOMOKIYO
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