 Further to this functional deficiency, was a twofold practical deficiency.For though one was "only" to answer "one's own" ringing code, every party on the same subscriber line could hear all the ringing codes.This meant firstly, frequently ringing telephones were a disruptive annoyance, as each party on the line had to stop to listen every time the telephone rang in order to determine according to the ringing cadence if they were the party being called on any given ring.