A method for seizing a phone line. Widely used for residential phones and key systems, the two wires in the phone line (tip and ring) are bridged together through a resistor when the handset is taken off-hook. The CO detects the current in the loop. Contrast with ground start.
A signaling technique used in single line, multiline telephones, and key telephone systems (KTSs) to start, or seize the line between the terminal and the central office switch. With loop start signaling, the telco central office switch provides battery.When the handset of the telephone is lifted, the electrical loop is completed and dc current flows across the circuit.The central office switch detects that fact, bridges the line, assigns a register, and returns dial tone for an outgoing call, or connects an incoming call, as appropriate. Loop start also is used in some PBXs, although it is unusual due to issues of glare, or collision between incoming and outgoing calls. See also glare, ground start, loop, and register.