05369690 is referenced by 8 patents and cites 18 patents.

A telephone circuit is provided for distinguishing between a normal incoming telephone call and a test telephone call. When the telephone is polled from a central station to cause it to undergo a self-test routine, a ringing signal is used which consists of a series of three ringing signals each lasting less than a predetermined time. Consequently, when such a ringing signal is received, a relay remains open so that there is no audible ringing tone. The system thus enables a testing routine to be carried out by the telephone without causing the telephone to ring.

Title
Telephone call detecting circuit and a method of remotely accessing and testing a telephone
Application Number
7/927274
Publication Number
5369690
Application Date
September 11, 1992
Publication Date
November 29, 1994
Inventor
John J Comfort
Basingstoke Hampshire
GB
Agent
Davis Hoxie Faithfull & Hapgood
Assignee
Mars Incorporated
VA, US
IPC
H04M 15/00
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