Such conditions are properly recognized in ground start signaling, a protocol primarily used on trunks between switching systems.
Modern loop-start trunks often provide additional methods supervision to avoid the far-end-disconnect problem.
Typically, it is implemented by removal of battery voltage from the line for a short period of time, resulting in loss of loop current.
Kewlstart is a coined term created in the Asterisk PBX open-source software community for an extension of loop start signaling for FXS and FXO telephony interfaces which adds disconnect supervision.
[3] Disconnect supervision is implemented as an open switching interval (OSI), a period of several hundred milliseconds during which the loop current is interrupted.
Some switching systems remove loop battery voltage for about 250 ms within 6 seconds after the far-end party disconnects.