GB1574599A - Fault indication in repeatered telecommunications transmission-line - Google Patents

Description

(54) FAULT INDICATION IN REPEATERED TELECOMMUNICATIONS TRANSMISSIONlINE (71) We, THE PLESSEY COMPANY LIMI TED, a British Company of 2/60 Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to repeatered telecommunications transmission-line systems and is particularly concerned with the detection, reporting and indication of faults occurring in such systems under operational conditions.

The invention is typically applicable to systems in which each direction of transmission between two terminal stations involves a separate coaxial cable or line, and wherein the power supplies at repeater stations along the line are serially-derived from sources provided at the - terminal stations.

In such transmission systems the power supply arrangements involve power-supply filters at the terminal stations of the line and at the opposite sides of each of the repeaters, the filters being so arranged that the highfrequency signals forming the telecommunications transmission traverse the whole line with its terminal and repeater amplifiers whereas the D.C. supply currents, although extending over the line, are committed to branch paths at the terminal and repeater stations; typically a Zener diode (in the branch path at each repeater station) being employed in the provision of a local stabilised D.C. supply. Conveniently the power supply circuit alluded to may be used as a bearer for control and supervisory signalling between stations of the transmission line.

The object of the invention is to provide simple and reliable signalling means which enables faults which develop in an op era- tional repeatered transmission-line system to be reported promptly to one of the terminal stations to institute indications at that station so that the Iocation of the faults can be readily assessed.

According to the invention there is provided a repeater station in or for use in a transmission line providing telecommunications traffic transmission from a first terminal station to a second terminal station over a plurality of such repeater stations and employing supervisory signalling at a frequency below that of the band allocated to said traffic transmission, the repeater station being characterised in that it includes pulse-control equipment responsive to a sequence of one or more supervisory signal pulses incoming over the outgoing traffictransmission path of the repeater station in such manner that except in the presence of a reportable fault condition at the repeater station the pulse or pulses of the pulse sequence are effectively reproduced at the incoming trafflc-transmission path together with a suffix pulse pattern comprising one or more pulses and the or each pulse of said pattern is of the same for as the reproduced pulse or pulses.

Also according to thé invention the pulsecontrol equipment is additionally arranged for operation in such manner that when no supervisory signalling pulse is forthcoming over the outgoing transmission path within a predetermined period and in the absence of a reportable fault condition at the repeater station at least one supervisory pulse constituting a said suffix pulse pattern is generated and applied to the incoming transmission path and is repeated at regular predetermined intervals throughout the existence of the situation.

The details of the invention will be understood from the following description of the preferred method of carrying it into effect which should be read in conjunction with the accompanying drawing comprising Figs.

1 to 4.

Of the drawing: Fig. 1 represents in outline form terminal stations and repeater stations appropriate to one direction of a telecommunications transmission system using separate coaxial lines for each direction; Figs. 2 and 4 show such portions of terminal stations TSB and TSA respectively of the line system of Fig.

1 as will assist in the understanding of the invention; whereas Fig. 3 is a simplified circuit diagram typifying the repeater stations of said line transmission system.

GENERA=Referring to Fig. 1 the arrow TT represents the direction (right to left) of high-frequency telecommunications transmission between the terminal stations TSA and TSB by way of the coaxial line COAX which is provided with the spaced repeater stations RS1 to RSN of which five are outlined. The other direction of transmission would be catered for by a second cable with all the equipments directed the other way.

In Fig. 1 the high-frequency telecommunications transmission signals, typically comprising F.D.M. (frequency division multiplex) channels arranged in groups and supergroups, are injected into the outgoing transmission path OTPA at terminal station TSA.

The transmission signals extend over the line-amplifier AA at the terminal station, and are connected over a first section of the coaxial line to repeater station RS1 for advancement over line-amplifiers A1, A2 ... AN--2, AN-1 and AN of the five repeater stations represented. The transmission signals are duly received, at terminal station TSB. over the final section of coaxial line by lineamplifier An which serves the incoming transmission path ITPB.

In accordance with known practice, the line-amplifier of at least some of the successive repeater stations are each provided with a monitor/regulator device, operative for level-control purposes, in known manner by a so-called pilot frequency signal included in the telecommunications transmission band of the system. These devices, each designated MR (with a subscript 1 ... N appropriate to the station) are additionally arranged to produce a fault signal at an individual alarm lead (such as lead AL of repeater station RSN) upon the particular monitoring device detecting an excessive change of transmission level at the repeater amplifier.

Such a change may arise, for example, from a disconnection or short-circuit fault in the cable length extending to the next station (leftward) in the direction of telecommunications transmission.

Each of the repeater stations also includes a pulse-control equipment, such as PCI, PC2 ... . . PCN and this included in a circuit branch separated from the through telecommunications transmission-path by the two powersupply filters (not shown) of the repeater station. The pulse-control equipment of each repeater station is responsive to so-called supervisory pulses normally incoming to it, at prescribed intervals, from the direction of the terminal station TSB, and its behaviour, in respect of generation of outgoing supervisory pulses in the direction of terminal station TSA, is determined by (a) the condition of the line-amplifier alarm lead of the station, and (b) the requisite persistence or otherwise of the incoming supervisory signalling function.

It is to be noted that supervisory signalling is effected in the opposite direction to the direction of the telecommunications traffic transmission, thus again referring to Fig. 1, supervisory transmission sequence is initiated by a single 10()as pulse produced every 0.3 sec. by a time-pulse generator TPG located at terminal station TSB.

When the initial 100,as pulse of a supervisory signal sequence is received at the nearest repeater station RSN, it is applied over a power-supply filter and pulse input lead PIL to pulse-control equipment PCN.

Assuming that the monitor/regulator device MRN of station RSN is not communicating a fault signal to equipment PCN, and that the station is fully operational, the pulsecontrol equipment responds by repeating the received 100,,as pulse to the output lead POL and by generating an additional similar pulse at that lead. The repeated pulse and the newly-generated pulse occur at 300,as intervals. Thus the repeater station nearest to terminal TSB receives one supervisory pulse every 0.3 sec. and promptly advances two supervisory pulses to the next station (RSN-1) along the line. All the repeater stations are operatively identical and indeed the pulse-control equipment of each of them (under "no-fault" conditions), is arranged to produce, at its output lead, one pulse more than it receives.It can therefore be deduced that, if traffic transmission over the line is being performed without reportable faults, the terminal station, TSA will, as a result of a single pulse generated at station TSB, receive a sequence of N+1 supervisory pulses; where N represents the number of repeater stations in the line.

At terminal station TSA each sequence of incoming supervisory pulses, occupying merely the initial portion of the 300 m.s interval timed at station TSB, is extracted by the power-supply filter thereat and extended to a suitable indicator unit IU. This preferably includes a pulse-counting device, operable by pulses of each incoming pulsesequence, a count display device, a comparator for anticipated and actual counts and an alarm device operable under fault conditions signified by disparity between the counts. Under "no-fault" conditions the successive received sequences are as anticipated (N+1) and no alarm is raised.

Still referring to Fig. 1 the effect of faults occurring at repeater station will be briefly considered.

The pulse-control equipment, PC1 to PCN, of each repeater station, besides being organised, under "no-fault" conditions, to repeat each received supervisory pulse and to add one such pulse to the output series, is operative as follows: (a) In the absence of any incoming supervisory pulse for a defined period (0.5 sec.), it will then generate an outgoing supervisory pulse of 100try: the pulse (simulating the sequence initiating function at station STB) being reproduced every 0.3 sec. for as long as there are no incoming pulses.

(b) When an alarm condition is forthcoming (over lead AL) from monitor/regulator device (to signify an excessive change of the state of the line amplifier) the output supervisory pulses are inhibited regardless of whether incoming pulse-sequences are being received or not. Failure of the local power supply would have the same result.

When circumstances appropriate to (b) above develop at a repeater station the disabling of the pulse-control equipment of that station ensures that transmission of supervisory pulses to the next repeater station to the right ceases. Accordingly the situation outlined at (a) above arises at the lastmentioned station, so that after a delay of 0.5 sec. it produces a single outgoing supervisory pulse and this will be reproduced every 0.3 sec. for as long as the fault persists. It can be deduced that as a result of each pulse a new supervisory signalling sequence is initiated, each sequence involving the performance of the "add-one-pulse" function by the control equipments of the remaining repeaters the path to the terminal station TSA.This ensures that each resultant pulse series, duly received at the latter, comprises as many pulses as there are repeater stations between the one that raised the alarm and station TSA. Therefore a sequence of 47 pulses means that the fault was detected at repeater station RS4s. This pulse sequence (and its successors if the fault persists) is applied to indicator unit IU of the terminal station. The indicator unit is pre-set to anticipate N+l pulses in each such sequence, and is preferably arranged so that when it has detected a disparity in respect of each of a predetermined number of successive sequences (say eight), it will initiate an alarm to call the maintenance officer, who can then deduce the fault location from the numerical display.

SUPERVISORY INITI"ATION-'TERMI- NAL STATION TSB--Fig. 2 shows sufficient of station TSB to enable the supervisory signalling procedure to be repetitively initiated by a single short duration pulse sent from it, over the power supply path involving the coaxial cable. It is to be understood that the satisfactory operation of amplifier A3 alone ensures that the monitor/ regulator device MRB associated with it, will maintain gate GB in the primed condition. In this circumstance, a signal occurring at lead TPC every 0.3 sec. is advanced to the pulse-generator PG which thereupon produces a pulse of 100,,as duration.This pulse, representing the initial pulse of a supervisory signalling sequence, is coupled to the coaxial cable CB by way of transformer BTR included (together with capacitor BC1 and inductor BI) in the low-pass section of the power supply filter BPSF of station TSB. The pulse is isolated from the terminal amplifier by the high-pass function of capacitor BC2.

It is to be noted that a positive voltage source PFB is coupled over the filter to line and that this source, together with a counterpart source PFA in a similar filter APSF at the remote terminal station TSA, enables stabilised supplies to be produced at each intermediate station of the unidirectional transmission line. Known variants to these power-feeding arrangements may all be used including the use of intermediate power-feeding repeater stations, providing the facility for pulse-signalling between the terminal stations of the line is retained.

THE INDICATOR UNIT-Part of the circuit arrangements of terminal station TSA including the indicator unit IU is shown in Fig. 4. High-frequency signals constituting the outgoing telecommunications traffic at path OTPA are extended over amplifier AA and the power supply filter APSF to the outgoing transmission cable CA. The powersupply source PFA is also connected to the cable by filter APSF to cater for the provision of power supplies, as aforesaid, at the repeater stations. Incoming supervisory pulses also forthcoming over cable CA are extended to pulse detector PD of the indicator unit by way of the filter APSF. Detector PD repeats the pulses of each sequence to a counter comprising unit, ten and hundred sections UC, TC and HC respectively; the counter controlling a resettable display DIS and exercising control upon the comparator COM.The pulse detector PD also repeats incoming pulses to the input presence detector IPD. This changes its state on the arrival of the first pulse of a series, and reverts to normal at end of pulse series, whereupon it applies an operate signal to the comparator. The comparator is preset according to the anticipated number of pulses in each sequence, and when said operate signal is received by it, a comparison is made between the anticipated count and the pulsesequence count registered by the counter.

The signal derived from detector IPD also causes the delay device RD to extend a pulse over lead RS to reset the counter and its display. Each time a disparity between the anticipated and actual counts is detected by the comparator it extends a pulse to the counter EC. This is arranged so that after a predetermined number of successive disparities (say 8), an alarm-initiating signal would be applied to device ALM. Additionally the counter EC may be employed to maintain the digital display intact.

REPEATER STATION-An abbreviated diagram of a typical repeater station RS of the transmission line is shown in Fig. 3. The apparatus is interposed between incoming and outgoing coaxial cable lengths CI and CO respectively which connect to the individual power supply filters 1PSF and 2PSF.

These filters are identical with that described in connection with Figs. 2 and 4. Highfrequency telecommunications signals, includes ing a pilot signal waveform for level control purposes and forthcoming over cable CI from the direction of terminal station TSA, are isolated, by filter lPSF, and extended to line amplifier A and thence over the highpass section of filter 2PSF to the outgoing cable.

The monitor/regulator device MR is sensitive to the level of the pilot waveform at the output of the amplifier normally and serves to regulate the amplifier. However if an excessive change of level occurs at the amplifier the device MR will apply an alarm signal to the pulse-control circuit PC over lead AL.

Within the typical repeater station, a branch path involving Zener diode Z and low-pass filter LPF (between filters lPSF and 2P5F) enables a stabilised D.C. power supply for the repeater to be derived from the diode.

Supervisory pulses of 100,,as duration, and generally occurring at 300,us intervals and constituting streams commencing at 300 m.s.

intervals. are, under normal conditions, duly forthcoming over cable CO to the typical repeater. Each pulse is operative over AND gate GPI to activate the monostable device MS which produces a 100,us output pulse at lead X. The pulse at lead X is extended to the appropriate input lead of logic circuit LOG. Under satisfactory working conditions, no alarm condition is forthcoming at lead AL of the logic circuit so that the latter is not disabled and the differentiated trailingedge of the lead X pulse causes a 100,as pulse to be produced by the outgoing pulse generator OPG. This pulse is directed over filter lPSF and cable CI in the direction of station TSA, and other incoming supervisory pulses are likewise repeated in the opposite direction to the high-frequency telecommunications transmission.

The pulse derived from generator OPG is atso operative to disable the input gate GPI to obviate response to any spurious transient signals.

Each incoming supervisory pulse coming over pulse input gate GPI besides being applied to device MS is connected to the bistable device BS which in conjunction with monostable devices MSS and MSR are duly to be concerned with the generation of an additional pulse at the end of any incoming pulse series however many pulses this series contains. In this respect, assuming a succession of incoming pulses (occurring at 300us intervals) each one of them effects a change of state of device BS to actuate one or other of the pulse-delay devices MSS or MSR.

The output leads of devices MSS and MSR are both coupled to input lead Y of the logic circuit LOG, and the inbuilt delay of the two devices is such that the one which is actuated produces a condition at lead Y which is delayed by 300ups with respect to that which appeared at lead X (as a result of the incoming supervisory pulse). Indeed the lead Y condition would be coincidental with the lead X condition arising from the next occurring incoming supervisory pulse (if any). The requisite condition at lead X or Y, or both of them, is operative in the logic device LOG to cause generator OPG to produce, at the end of the sequence, an additional outgoing supervisory pulse, corresponding in spacing and duration to its predecessors.

The other operation feature of the pulsecontrol equipment PC of the typical repeater station is that it has the ability to produce appropriately spaced supervisory pulses each constituting the initiation of a supervisory signalling sequence encompassing all stations to station TSA. The situation arises as a result of any sustained interruption of supervisory signalling from the station immediately to the left. For this purpose the equipment PC is provided with an interruption detector device IDD and an interval timer IT. Device IDD responds to each incoming supervisory pulse and includes a timing element which is set, to present an activating signal to the interval timer, if any break of 0.5 sec. or more arises in the reception of supervisory pulses. The interruption detector always remains available for re-setting on the resumption of incoming supervisory signals, but meantime the activated interval timer produces pulses at 0.3 sec. intervals which correspond to those at source TPC in Fig. 2.

Each of the pulses, applied over lead Z to the logic device LOG, is then operative, in the absence of an alarm signal at lead AL, to cause device OPG to generate the required outgoing sequence-initiating supervisory pulse.

The supervisory scheme hereinbefore described may be adapted for the notification of failures or unusual situations which may develop at that terminal station from which supervisory sequences are initiated, or at any socalled main power-feeding repeater stations included in the route and interspersed with normal or so-called dependent repeater stations of the kind hereinbefore described Accordingly to cater for four situations which are to be subjected to monitoring, the pulse-control equipment at each such repeater station of the line would be modified to add up to four pulses to the number received; the sequence being equatable to that of four normal or so-called dependent repeaters.The modified equipment, after reproduction of any incoming pulse or pulses, would provide: (1) No pulses under a power failure situa tion, (2) One pulse under a pilot failure situa tion produced under control of a suit able detector.

(3) Two pulses in the event of removal of an equipment mounting board.

(4) Three pulses if access to the station has been gained by forced entry.

(5) Four pulses if the station is function ing normally.

If incoming pulses are discontinued the output pattern of one of four pulses (according to the prevailing conditions within the repeater station) is repetitively generated by the modified pulse-control equipment; generation being initiated by the local interruption detector device such as IDD previously referred to.

In addition a facility may be provided at the repeater station to make two of the alarms non-urgent by gating the alarm signal with a multivibrator with a 4.5 second "on" 4.5 second "off" sequence, this will cause the display at the terminal station to alternate between the two pulse totals.

Another modification at the terminal station may also be provided to give an urgent alarm should there be say 16 successive error counts, over 5.3 seconds, and a non-urgent alarm should there be more than 8 successive errors.

The effect of the modifications outlined is that they enable an alarm condition to be signalled to the terminal station as hereinbefore described with the additional facility of continuing to monitor that part of the system lying between the station which initiated the alarm condition and terminal station with the display.

WHAT WE CLAIM IS: 1. A repeater station in or for use in a transmission line providing telecommunications traffic transmission from a first terminal station to a second terminal station over a plurality of such repeater stations and employing supervisory signalling at a frequency below that of the band allocated to said traffic transmission, the repeater station being characterised in that it includes pulse-control equipment responsive to a sequence of one or more supervisory signal pulses incoming over the outgoing traffictransmission path of the repeater station in such manner that except in the presence of a reportable fault condition at the repeater station the pulse or pulses of the pulse sequence are effectively reproduced at the incoming traffic-transmission path together with a suffix pulse pattern comprising one or more pulses and the or each pulse of said pattern is of the same form as the reproduced pulse or pulses.

2. A repeater station as claimed in claim 1 in which the pulse-control equipment is additionally arranged for operation in such manner than when no supervisory signalling pulse is forthcoming over the outgoing transmission path within a predetermined period and in the absence of a reportable fault condition at the repeater station at least one supervisory pulse constituting a said suffix pulse pattern is generated and applied to the incoming transmission path and is repeated at regular predetermined intervals throughout the existence of the situation.

3. A repeater station substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawing.

4. A repeatered telecommunications-line transmission system incorporating repeater stations of the kind claimed in claim 1, 2 or 3.

5. A repeatered telecommunications-line transmission system as claimed in claim 4 and including first and second terminal stations having first and second fault supervisory signalling equipment respectively said first equipment including a pulse generator which connects a pulse to the transmissionline at regular intervals each such pulse being the initiating pulse of a supervisory signalling sequence normally embracing all repeater stations and the second equipment includes means for registering supervisory pulse sequences received over the line together with display and alarm devices operative to signify the existence or otherwise of a fault condition.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. develop at that terminal station from which supervisory sequences are initiated, or at any socalled main power-feeding repeater stations included in the route and interspersed with normal or so-called dependent repeater stations of the kind hereinbefore described Accordingly to cater for four situations which are to be subjected to monitoring, the pulse-control equipment at each such repeater station of the line would be modified to add up to four pulses to the number received; the sequence being equatable to that of four normal or so-called dependent repeaters.The modified equipment, after reproduction of any incoming pulse or pulses, would provide: (1) No pulses under a power failure situa tion, (2) One pulse under a pilot failure situa tion produced under control of a suit able detector. (3) Two pulses in the event of removal of an equipment mounting board. (4) Three pulses if access to the station has been gained by forced entry. (5) Four pulses if the station is function ing normally. If incoming pulses are discontinued the output pattern of one of four pulses (according to the prevailing conditions within the repeater station) is repetitively generated by the modified pulse-control equipment; generation being initiated by the local interruption detector device such as IDD previously referred to. In addition a facility may be provided at the repeater station to make two of the alarms non-urgent by gating the alarm signal with a multivibrator with a 4.5 second "on" 4.5 second "off" sequence, this will cause the display at the terminal station to alternate between the two pulse totals. Another modification at the terminal station may also be provided to give an urgent alarm should there be say 16 successive error counts, over 5.3 seconds, and a non-urgent alarm should there be more than 8 successive errors. The effect of the modifications outlined is that they enable an alarm condition to be signalled to the terminal station as hereinbefore described with the additional facility of continuing to monitor that part of the system lying between the station which initiated the alarm condition and terminal station with the display. WHAT WE CLAIM IS:

1. A repeater station in or for use in a transmission line providing telecommunications traffic transmission from a first terminal station to a second terminal station over a plurality of such repeater stations and employing supervisory signalling at a frequency below that of the band allocated to said traffic transmission, the repeater station being characterised in that it includes pulse-control equipment responsive to a sequence of one or more supervisory signal pulses incoming over the outgoing traffictransmission path of the repeater station in such manner that except in the presence of a reportable fault condition at the repeater station the pulse or pulses of the pulse sequence are effectively reproduced at the incoming traffic-transmission path together with a suffix pulse pattern comprising one or more pulses and the or each pulse of said pattern is of the same form as the reproduced pulse or pulses.

2. A repeater station as claimed in claim 1 in which the pulse-control equipment is additionally arranged for operation in such manner than when no supervisory signalling pulse is forthcoming over the outgoing transmission path within a predetermined period and in the absence of a reportable fault condition at the repeater station at least one supervisory pulse constituting a said suffix pulse pattern is generated and applied to the incoming transmission path and is repeated at regular predetermined intervals throughout the existence of the situation.

3. A repeater station substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawing.

4. A repeatered telecommunications-line transmission system incorporating repeater stations of the kind claimed in claim 1, 2 or 3.

5. A repeatered telecommunications-line transmission system as claimed in claim 4 and including first and second terminal stations having first and second fault supervisory signalling equipment respectively said first equipment including a pulse generator which connects a pulse to the transmissionline at regular intervals each such pulse being the initiating pulse of a supervisory signalling sequence normally embracing all repeater stations and the second equipment includes means for registering supervisory pulse sequences received over the line together with display and alarm devices operative to signify the existence or otherwise of a fault condition.