The full name of common cooperative English noun abbreviations
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
