Why is it not possible to disconnect an incoming call in landphone

In the case of a land phone, the same physical 'two wire' path circuit carries both the speech and ringng. The exchange makes use of a 80V current to activate ringing of the telephone. A ringing phone can only be stopped by giving a loop on the 'two wire' circuit, which is effected by lifting the reciever. The path is broken when the reciever is placed back and hence the call is disconnected. However in the case of a mobile phone, seperate channels are used for speech and signals. Only when the user answers the call is the speech channel is connected. On the other hand when the phone rings the signal channel is connected, which carries the ringing inforamtion. A 'stop ringing' information is send when the user disconnects by pressing the end call button, thus deactivating the call.


[1] http://www.thehindu.com/todays-paper/tp-features/tp-sci-tech-and-agri/disconnecting-call/article3225505.ece