Browse Prior Art Database

In Band Signalling System

IP.com Disclosure Number: IPCOM000086466D
Original Publication Date: 1976-Sep-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Boisseau, M: AUTHOR [+3]

Abstract

The present signalling system is mainly applicable to long distance tie lines having a two-wire interface. A compelled signalling (i.e., with acknowledgement) is provided with only two signalling frequencies.

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In Band Signalling System

The present signalling system is mainly applicable to long distance tie lines having a two-wire interface. A compelled signalling (i.e., with acknowledgement) is provided with only two signalling frequencies.

The figure shows two exchanges A and B, a tie line TL through which communications can be established between these exchanges, and the interfaces between tie line TL and these exchanges, respectively.

Each interface comprises:

- A two position switch, SA, SB: position 1 for signalling status and idle status, position 2 for talking status.

- Two frequency generators GF1 and GF2 capable, under an appropriate control, to transmit audio frequency F1 or F2, respectively.

- Two frequency receivers RF1 and RF2 capable of detecting frequencies F1 or F2, respectively. These receivers are so designed that they only detect a quasi pure and continuous frequency.

- A control logic under which the control of all operations is made.

Assuming that exchange A wants to call exchange B, the systems operates as follows.

Generator GF1 of the A interface transmits frequency F1 as being a SEIZE signal.

At the B interface, when receiver RF1 detects this signal, generator GF2 transmits frequency F2 as being a SEIZE ACKNOWLEDGE signal, after a predetermined delay T1.

Frequency F2 is then detected by receiver RF2 of A interface. If it is detected within a predetermined period of time T2 (larger than T1) after sending the initial SEIZE signal, it is interpreted by the A logic as a SEIZE signal coming from the B interface and a call contention is then detected (simultaneous call from the two exchanges A and B).

If it is detected after a period of time higher than T2, it is interpreted as a SEIZE ACKNOWLEDGE signal. Frequency generation is stopped and the A logic turns on switch SA from 1 to 2.

The call connection is then established, and the subscribers involved can talk.

When the talk is finished and assuming that the subscriber from ex...