A few definitions, just in case ...
Loop closure - most residential phone service starts with a pair of wires for each phone number at a residence. These pairs go all the way to the local telephone central office (CO). They are normally open (NO). When someone at the residence lifts the telephone receiver the pair of wires gets connected (loop closure). This causes current to flow on the wires and this current is detected at the CO as somebody wanting to make a call. The CO then puts a dial tone on the current. Once the CO detects dialing, the dial tone is removed and the call setup proceeds.
Line seizure - a telephone line (most likely in a PBX) detected to be free - not in use. A person at an extension lifts the receiver and presses "9" or what ever code is required to grab an outside line. The PBX the connects that extension with that telephone line. If there are no free outside lines, the extension user gets a busy signal and has to wait. The PBX is said to be 'courteous' in this case.
Line seize relay - used in security systems. When a security system detects the need to call out and report some issue, courtesy goes out the window. The security system 'orders' the line seize relay to override what ever else is going on on the line and make the outgoing call.
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Topic: ds7000 with RJ31x (Read 16631 times)