Line signaling is a class of telecommunications signaling 
protocols. Line signaling is responsible for off-hook, ringing signal, answer, ground start, on-hook unidirectional supervision messaging in each direction from calling party to called party and vice versa.

Line signaling is a class of telecommunicationssignaling protocols of telephone numbers of called party and in more modern line-signaling protocols, the calling party as well.


* Concerned with conveying information on the state of the line or channel.


* Example : on hook , off hook , ringging signal 


* Is a supervisory signal and may appear in the circuit anytime


* used to set up and clear down the call and represent events that occur on the trunk such as seizure , proceed-to-send, answer and clear forward.