Browse Prior Art Database

Signalling System for Two Wire Tie Line

IP.com Disclosure Number: IPCOM000074717D
Original Publication Date: 1971-Jun-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Garcia, J: AUTHOR [+3]

Abstract

This signalling system provides an automatic connection between two Private Branch Exchanges PBX A and PBX B. It uses two tones in the audio band FA = 2400 cps and FB = 2600 cps.

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Signalling System for Two Wire Tie Line

This signalling system provides an automatic connection between two Private Branch Exchanges PBX A and PBX B. It uses two tones in the audio band FA = 2400 cps and FB = 2600 cps.

The tones are transmitted individually, one in each direction and may be recognized even though both are present on the line. Signalization is composed of forward and backward signals. By convention a forward signal is sent in the direction from the calling party to the called party.

When a Subscriber of PBX A calls for an extension of PBX B, it stops transmitting the frequency tone FA, 250 ms later the receiver of PBX B. detects that FA has dropped. PBX B stops transmitting its tone FB for a while and then again sends a tone FB 200 ms long, to indicate that B is ready to receive dial pulses ("proceed to send"). The dial pulses are generated by the outpulsing program of PBX A; the break-to-make ratio of the FA dial pulses is chosen according to PTT regulations.

The system is composed of an oscillator OSC, a receiver REC, an interface telephone line/network, and a logic control card.

The receiver REC is always connected to the telephone line to detect supervisory signals and convert them into signals suitable for the logic control card. During transmission and reception of supervisory signals, relay RA is energized, so that low-pass filter LPF, whose cutting frequency is 450 cps, is inserted into the speech path. This allows the calling party to receive ring-back tones and prevents it from receiving the signalling frequencies. Moreover, LPF prevents the noises (music or speech) coming from the calling party from interfering with the signalling frequencies. Indeed, should a continuous signal at signalling frequency FA or FB due to speech or music be applied to the network side of the receiver, relay RA is activated 10 ms later, so that the signal drops on the line, under the action of LPF. Then relay RA returns to the rest status and the process is repeated until the simulation signal goes off. As the continuous periodic wave is split under the form of an on/off signal at a speed which is too high for a supervisory tone, this simulation tone will be ignored by the tie line receiver. However, if the received signals are supervisory tones, the splitting process described above does not disturb the operation, since the receiver input (high-pass filter HPF) is connected directly to the same line carrying the supervisory signals.

After high-pass filtering and amplification, the two signalling frequencies (FA, FB) are separated into their respective channels by the band-elimination filter. One section of the filter can be switched from band-elimination to band-pass filter according to the tie line status, i.e.: - idle status, to recognize...