American Telephone and Telegraph Company and At&t Information Systems

Robert L Ducharme

Jeffrey A Cromwell

A dial tone detection arrangement for a PBX which provides a dial tone detection notification feature to a calling party is disclosed. The disclosed arrangement relieves the calling party from the burden of aurally monitoring the receiver of a station while waiting for receipt of central office (C.O.) dial tone. The dial tone detection notification feature is advantageous under conditions where the calling party places a call to a called station served by the C.O. and experiences extensive delays, e.g. 30 minutes, in the receipt of C.O. dial tone. The dial tone detection arrangement utilizes an algorithm to establish a connection between a dial tone detection circuit of the PBX and a trunk port connected to a C.O. via a switching network. The dial tone detection circuit monitors the C.O. via the trunk port for the presence of dial tone indicative of C.O. availability. The calling party may now go 'on-hook' and await a notification at the calling station indicative of the detection of dial tone. In response to the notification, the calling party goes 'off-hook' and a call connection between the calling and called stations is established.

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Arvada, CO, United States of America

Robert L Ducharme