"Yet another scheme is the ringing counting scheme where by the remote control site places a call and lets the line ring a set number of times..."

Beware! In some (most? all?) systems, the ringing tone heard by the caller is generated by the caller's local exchange, while the ringing voltage sent to the called line is generated independently by the called local exchange.
Therefore, there is no guarantee that the number of rings heard by the caller will be the same as the number of rings "heard" by the called line!