Alexander Graham Bell filed the patent for the telephone over one hundred years ago. Landlines use much the same technology to ring to alert the user of an incoming call that they did when they first came into use. Cell phones use a slightly different technology to warn the user of an incoming call.
Land Line Ring
Land lines rely on a change in voltage to know when to ring. When someone dials the number for a landline phone and the phone company routes the call to its intended destination, a 90 volt signal comes through and triggers the phone’s ringing hardware.
How Cell Phones Ring
Voltage signals mean nothing to a cell phone, but instead cell phones contain software that allows the phone to recognize when it receives a call. This software then calls up the procedures that cause the phone to ring. This procedure identifies custom ring tones if the user has set one up.
VOIP phones work in manner that combines the operation of land lines and cell phones. The call comes into the phone and the computer hardware processes it to determine that it is supposed to go to the VoIP phone connected to the computer. The computer then sends out a 90 volt signal that causes the VoIP phone to ring. Because the Internet was not dewsigned to carry voice traffic, communications on VoIP phones can be interrupted during periods of high traffic.