Shulou(Shulou.com)06/01 Report--

VOIP:Voice over IP

PSTN:Public switched telephone network started at 1900s.

PBX:Private branch exchange

Tip and ring positive and negative wires represent the two wires that make up the telephone wiring circuit. Tip is another name for positive wire; Ring is another name for negative wire. The voltage of tip line is positive, the voltage of RING is negative, and the voltage between them is usually 48V.

CO: phone company central office

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