| 摘要 |
Controlled activation of a message-waiting light of a telephone unit of a PBX system, that is coupled over a two-wire link to a foreign exchange subscriber circuit terminating a digital communication link, is carried out by hardware and software modifications to each of FXO and FXS channel units at opposite ends of the digital communication link. These modifications are effective to rob redundant signalling bits of extended superframe format time division multiplexed digital communication signals to transport a prescribed request code, that instructs the FXS circuit to generate a message-waiting light driving signal on the tip-ring pair to the message-waiting phone.
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