Browse Prior Art Database

Detecting the End of Go Ahead Tone

IP.com Disclosure Number: IPCOM000084283D
Original Publication Date: 1975-Oct-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 29K

Publishing Venue

IBM

Related People

Garofalo, FJ: AUTHOR [+2]

Abstract

In communication based data transmission systems such as telephone exchange systems having extensions to which data transmission devices are connected, it is often useful to use a control tone such as a dial tone as a "go-ahead" signal from the central apparatus to the remote terminal, to indicate that the central apparatus is ready to receive data from that terminal.

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Detecting the End of Go Ahead Tone

In communication based data transmission systems such as telephone exchange systems having extensions to which data transmission devices are connected, it is often useful to use a control tone such as a dial tone as a "go- ahead" signal from the central apparatus to the remote terminal, to indicate that the central apparatus is ready to receive data from that terminal.

In order to discriminate against noise signals, a go-ahead signal is not considered to be valid unless it continues for at least a certain length of time and, therefore, its termination is the critical event in initiating the data transmission. However, not all gaps in such a signal indicate a valid termination, particularly since a signal is often composed of two or more frequencies which beat against each other, creating short nulls at regular intervals in the signal.

Additionally, it is usually desirable to provide a period of time after the end of the go-ahead signal before data transmission commences, in order to accommodate timing requirements at the interface and input apparatus of the central equipment.

The illustrated detector meets these requirements. Counter 10 is provided to serve the basic function of determining a minimum length valid go-ahead signal. Counter 12 is provided to provide the function of discriminating between a valid null and the true end of a go-ahead signal. It is also operative to clear counter 10 of false, noise generated counts. Latches 14 and 16 and their associated logic are operative, to provide a delay of at least 40 milliseconds after a valid termination of the go-ahead dial tone, to provide the described settling time.

To operate in this manner, dial-tone signals which have been squared and shaped are prov...