Communication facility integrity checking arrangement

In a telephone switching system wherein common control equipment is seized at a first switching office to establish a call over an interoffice connection to a second switching office and is released subsequent to an interchange of signals along a cross-office path between said equipment and the outgoing trunk at said first office selected to serve said call,

• an arrangement for verifying the integrity of said interoffice connection comprising
• means included in said outgoing trunk operated in response to the receipt of a first one of said interchange signals from said equipment for thereupon transmitting a seizure signal over said interoffice trunk to said second office,
• means in said second office responsive to the receipt of said seizure signal for sending a seizure acknowledgement signal of designated polarity to said outgoing trunk,
• means in said second office operated after a preselected timeout interval for reversing said designated polarity, and
• means in said outgoing trunk operated only in response to the receipt of said seizure acknowledgment signal of reverse polarity for returning a second one of said interchange signals to effect a release of said equipment.

An arrangement for verifying the integrity of a communication facility comprising:

• a plurality of terminal circuits,
• a switching network,
• common control means for establishing a channel across said switching network between a first and second one of said terminal circuits, said communication facility directly connecting said second terminal circuit with a third one of said terminal circuits,
• continuity checking means connected to said channel for thereacross exchanging check signals on a timeout basis with said second terminal circuit to test the continuity of said channel and released from said channel upon completion of said exchange of check signals,
• means in said second terminal circuit actuated by the receipt of a first one of said check signals from said continuity checking means for sending a seizure signal to said third terminal circuit over said facility,
• means in said third terminal circuit responsive to the receipt of said seizure signal for returning an acknowledgement signal of prescribed duration to said second terminal circuit, and
• means at said second terminal circuit actuated in response to said common control means controlling an establishment of said channel for inhibiting a sending of a second one of said check signals to said continuity checking means until after said acknowledgment signal has been received for said prescribed duration to allow said release of said common control means when said continuity is verified and to prevent said channel from remaining unnecessarily established upon the occurrence of a continuity check failure.

An arrangement for verifying the integrity of a communication facility between a trunk circuit in a first switching office and a line circuit in a second switching office and comprising:

• a W-Z relay circuit in the trunk circuit of the first office wherein both said W and said Z relays are differentially wound relays,
• means for placing said W-Z relay circuit in a first state on selection of the outgoing trunk circuit in the first office,
• means for placing said W-Z relay circuit in a second state on seizure and activation of supervision of said trunk circuit in said first office,
• means for placing said W-Z relay circuit in a third state on receipt of an off-hook seizure acknowledgment signal from said line circuit of the second office, and
• means for returning said W-Z relay circuit to its initial state on receipt of a subsequent on-hook signal of predetermined duration from said line circuit of the second office.

An arrangement for delaying the release of a sender in a toll office until verification of seizure of a line circuit in a distant office to check the integrity of the interoffice communication facility comprising

• a memory circuit at the toll office having four states,
• means for placing said memory circuit in a first state upon selection of an outgoing trunk circuit at the toll office,
• means for placing said memory circuit in a second state on transmission of a seizure signal over the trunk circuit to the distant office,
• means responsive to a seizure acknowledgment signal having a prescribed duration from the line circuit of the distant office for placing said memory circuit in a third state,
• means responsive to receipt of an on-hook signal from the line circuit of the distant office after said prescribed duration for returning said memory circuit to its initial state, and
• means responsive to the return of said memory circuit to its initial state for opening a cross-office path in said toll office to effect release of the sender therefrom.