The asserted RI signal lasts nearly exactly as long as the ringing on the telephone line - for example, 2.0 seconds per ring burst in North America. The RI signal follows the ringing pattern closely - in fact, it is possible for a computer program to detect distinctive ring patterns from the phone company by monitoring the transitions of the RI signal. If the phone line rings, for example, two short burts and then a long burst, the RI signal will imitate this pattern