Q.

On most PSTN telephone lines it seems, if a called party tries to hang up on a call but the caller keeps the line open, the call still stays connected for over 15 seconds. This lets the caller forcibly keep the callee’s line occupied. (But when the caller hangs up, the line is immediately released.) Why do phone companies do this to their called parties? Is there some kind of standard in the telecom industry that says that called parties, and not the caller, shouldn’t be able to disconnect their call until being on-hook for over 15 seconds?

A.

The reason this occurs is due to the equipment used to switch phone lines on and off. Some areas (usually rural areas) still have analog phone switching equipment – a mechanical relay is used to route the calls at the switch. It takes several seconds for the relays to release after a call. If one side of the circuit (phone line) remains open, the relay stays closed (connected). This doesn’t apply to newer, digital phone switches.