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What is the difference between loopstart, groundstart, and kewlstart signalling?
Views: 12189, Votes: 10

Posted:
12 Mar, 2006 - Brooks M.

Updated:
14 Mar, 2008 - Support D.
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Loopstart signalling is used by virtually all analog phone lines. It allows a phone to indicate on hook/offhook, and the switch to indicate ring/no ring.

Kewlstart is based on loopstart, but extends the protocol by allowing the switch to drop battery on the phone line to indicate to the phone that the other end of the party has disconnected the call. Most real phone switches, and almost no PBX's (except Asterisk, of course) support this feature. It is generally required for getting hangup notification.

Groundstart signalling is sometimes used by PBX's. If you don't know what it is, don't worry, you won't need it.
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