Loop Start vs. Ground Start Signaling

Analog Connections - Loop Start and Ground Start Signaling

Loop Start Signaling:

• When the phone is lifted off-hook, the phone connects tthe two wires, causing an electrical signal (48V DC voltage) to flow from the phone company central office (CO) into the phone. This is known as loop start signaling.


• Disadvantage:
  Glare problem occurs when you pick up the phone to make an outgoing call at the same time as a call comes in on the phone line before the phone has a chance to ring.


• Typically used home environments.
  

Ground Start Signaling:

• The grounding of the wires would signal the phone company to send a dial tone on the line. Using this type of signaling in PBX systems allows the PBX to separate an answering phone from an incoming phone line, reducing the problem of glares.


• Because of glare, most modern PBX systems designed for larger, corporate environments use ground start signaling.

Loop start vs. Ground Start Signaling

In order to receive a dial tone from the CO, the PBX must send a ground signal on the wires. This intentionally signals to the telephone CO that an outgoing call is going to happen, whereas using the loop start method of signaling just connects the wires to receive an incoming call or place an outgoing call.