GB2074424A

GB2074424A - Signal transmission systems

Info

Publication number: GB2074424A
Application number: GB8111601A
Authority: GB
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1980-04-21
Filing date: 1981-04-13
Publication date: 1981-10-28
Also published as: GB2074424B

Abstract

A signal transmission system comprises two terminal stations and at least one intermediate station with a number of regenerators disposed between each terminal station and the intermediate station and between each of the intermediate stations. Each intermediate station receives error or alarm signals from each of its regenerators in turn and assembles the signals so received into a multi-digit signal unit for all of its associated regenerators for forwarding to one or both of the terminal stations.

Description

SPECIFICATION Signal transmission systems The present invention relates to signal transmission systems and more particularly but not exclusively to optical fibre signal transmission systems.

When signal transmission lines are fitted with large numbers of regenerators, locating a particular regenerator on which a fault has occurred may be a lengthy process. Therefore, it is preferable to monitor each regenerator at regular intervals so that any build up of transmission errors over a fixed time interval may be detected. When metallic transmission lines are used a regenerator may be monitored by sending an address signal to that regenerator which then replies with a local error report.

However if the line is long it may take a substantial period to interrogate each regenerator in turn. Thus if an error occurs in a regenerator which is interrogated early in the sequence this error may give a false indication of the location of the fault when a later regenerator is being interrogated and it will take additional time before the control centre can establish which regenerator is actually at fault.

It is an object of the present invention to provide improved apparatus for monitoring regenerator stations in transmission systems.

According to the present invention a signal transmission system comprises first and second terminal stations, an intermediate station between the first terminal station and the second terminal station, and a plurality of regenerators between the first terminal station and the intermediate station and/or between the intermediate station and the second terminal station, the intermediate station including means for receiving and storing error or alarm signals from at least some of the plurality of regenerators and means to transmit data relating to the error or alarm signals on demand from one of the terminal stations for subsequent alalysis.

Preferably a plurality of intermediate stations are provided and there may be a plurality of regenerators between each pair or any pair of intermediate stations, each intermediate station having means for receiving and storing error or alarm signals from a respective plurality of the plurality of regenerators and respective means to transmit data relating to the error or alarm signals on demand from one of the terminal stations.

Each intermediate station may be arranged to receive and store error and alarm signals from a respective plurality of regenerators on each side of that intermediate station.

Each intermediate station may be arranged to interrogate each of its respective regenerators on one side thereof in turn on a first instruction from one of the terminal stations and to interrogate each of its respective regenerators on the other side thereof in turn on a second instruction from that terminal station.

Alternatively each intermediate station may be arranged to interrogate in turn each of its respective regenerators on an instruction from one of the terminal stations.

Preferably all intermediate stations are arranged to interrogate at the same time as each other their respective regenerators on one side and similarly to interrogate at the same time as each other their respective regenerators on the other side.

A transmission system in accordance with the present invention will now be described with reference to the accompanying drawings of which: Figure 1 is a schematic diagram of a transmission system in accordance with the present invention; Figure 2 shows a part of Fig. 1 in greater detail; Figure 3 is a timing diagram of signalling between an intermediate station of Fig. 1 and its respective regenerators; and Figure 4 is a timing diagram of signalling between one of the terminal stations of Fig. 1 and the intermediate stations.

Referring to Fig. 1 the line transmission system comprises two terminal stations 1 and 2 each with an associated fault display panel 3. Speech and data signals are transmitted digitally, for example utilising pulse code modulation, between the terminal stations 1 and 2 by four optical fibres 4 (only two of which are shown completely), A number of intermediate or power feeding stations (only two of which are shown) 5 and 6 are provided along the route and between each of the terminal stations 1 and 2 and its nearest intermediate station 5 or 6 and between each pair of intermediate stations 5 and 6 a number of regenerators 11 to 14, 25 to 28, 51 to 58 and 61 to 68 are provided to maintain the signal levels in the optical fibres 4.It will be appreciated that the number of regenerators between adjacent stations may not be eight, however the coding system adopted in the embodiment as subsequently described herein is based on a maximum of eight regenerators between adjacent stations.

Each regenerator has a respective supervisory unit designated by the same reference numeral with the addition of a prime (e.g.

regenerator 11 has a respective supervisory unit 11') which records any fault or alarm signals arising in any of the four systems of its respective regenerator and transmits information relating to the fault or alarm signals on demand. Fault or alarm signals pass from the regenerator 11 etc. to its respective supervisory unit 11' etc. by way of a repective fault highway 9.

As electrical power cannot be directly fed to the regenerators by way of the optical fibres 4, a metallic pair 8 is provided to feed a direct current at a suitable voltage to the regenerators 11 etc. and their associated supervisory units 11' etc. Each intermediate station 5 and 6 and the terminal stations 1 and 2 derive the suitable voltage from (for example) and a.c. mains electricity supply and may supply this power to, say, the four regenerators in each direction from an intermediate station (5, 6) in the case of the intermediate stations or to the respective four regenerators closest to each terminal station 1, 2 in the case of the terminal stations.At the regenerators 14, 54 and 64 the metallic pair 8 may include a transformer or capacitors (not shown) to prevent D.C. power from respective intermediate stations 5, 6 or terminal stations 1, 2 from affecting the D.C. power in an adjacent section. The D.C. blocking may alternatively or additionally be in the metallic pair 8 at the regenerators 28, 58 and 68.

Referring also to Fig. 2 it will be seen that the power for the regenerators 11 etc. and their associated supervisory units 11' etc. is taken from the metallic pair 8 from either side of a capacitor 80 which is in the centre of the primary winding of a transformer 81 by way of power leads 20. The secondary winding of the transformer 81 is connected to a transceiver (not shown) in the supervisory unit 11' etc. by way of leads 1 0.

It will be appreciated that each regenerator 11 to 14, 25 to 28, 51 to 58, and 61 to 68 includes eight amplifying systems (not shown) being one amplifying system in each direction for each optical fibre 4. The amplifying systems are arranged to convert light signals from their respective inputs to an electrical signal which is amplified and retransmitted by lasers for example to their respective outputs.

Each system is also arrnnged,to check the received signals (by bit parity for example) and to check the strength of th received and transmitted signals. Errors occurring in the received signal or weakness of the received or transmitted signal cause an alarm signal to be sent to the respective supervisory upit associated with the regenerator by way of the fault highway 9. The supervisory unit stores the alarm signal until it is interrogated as subsequently described and then clears the alarm if it is no longer present for the amplifying system.

It will be realised that weakness of the received signal indicates either a fault on the optical fibre 4 from the previous regenerator or a fault in the amplifying system or weakening of the laser in the previous generator. A weakening of the transmitted signal indicates a fault in the amplifying system of this regenerator or in the laser of this regenerator.

In order to simplify the description of the signalling and fault recording method now to be described the specification is written in relation to the terminal station 1 with its respective associated regenerators 1 1 to 1 4 the intermediate station 5 with its respective associated regenerators 51 to 58 and the terminal station 2 with its respective associated regenerators 25 to 28.It will be apparent that the signalling and interrogation procedure used by the intermediate station 5 and now to be described is used by the intermediate station 6 and any other intermediate station provided in synchronism with the intermediate station 5 and in relation to the respective associated regenerators 61 to 68. - Referring initially to Figs. 1 and 4 one of the terminal stations 1 and 2 which for the time being is functioning as the controlling station say terminal station 1 sends an interrogate code comprising a burst of 390 Hz tone representing a logic '1' bit followed by a similar burst of 450 Hz tone representing a.

logic '0' bit and a code of eight '0' or '1' bits the purpose of which is to identify a particular intermediate station 5 or the terminal station 2 which is to send expanded information as hereinafter described.

Refering also to Fig. 3 approximately 1 35 milli-seconds after the first logic 1 transmitted by the terminal station 1 each intermediate station 5, commences an interrogation of its respective regenerators 51 to 58 and the terminal stations 1 and 2 commence interrogation of their respective regenerators 11 to 14 and 25 to 28.

The terminal station 1 and the intermediate station 5 send tone signals towards the re- mote station 2 on the metaTh pair 8 as follows: A burst of 1300 Hz tone represArR,ting a logic '1' bit followed by a burst of 1700 Hz representing a logic '0' bit which indicate to the regenerator supervisory units 11' to 14' and g1 ' to 54' that an interrogation is about to occur.

The '1' and '0' bits are followed by two bits which may be either '1' or '0' signals and then a further two bursts of 1 700 Hz representing logic '00' which indicates that regenerators supervisory units 11' and 51' are td respond.

The regenerator supervisory units 11' and 51' respond to the demand by sending a logic '0' followed by a logic '1' followed by four bits indicative of any alarms or error signals from their two respective amplifying systems relating to the first of the optical fibres 4.

The regenerators 11 and 51 then send a similar series of signals in relation to their respective amplifying systems for each of the other three optical fibres 4 in turn.

On completion of this sequence the terminal station 1 and the intermediate station 5 interrogate the respective regenerator supervisory units 12' and 52' by sending a similar burst of tone signals on the metallic pair 8 towards the remote station 2 terminating with logic '01' signals. The regenerator supervisory units 12' and 52' return respective bursts of data relating to their respective amplifying systems for the four optical fibres 4.

The sequence is then repeated with the terminal station 1 and the intermediate station 5 addressing respective regenerator units 13' and 53' and 14' and 54' with respective interrogate signals terminating with logic '10' and logic '11'.

The terminal station 2 and the intermediate station 5 now use the above signalling sequence sending interrogate signals on the metallic pair 8 in the direction of the terminal station 1 and receiving signals back from their respective addressed regenerator supervisory units 25' to 28' and 55' to 58'. Thus regenerator supervisory units 25' and 55' respond to interrogate signals terminating with logic '00', units 26' and 56' to signals terminating with logic '01', units 27' and 57' to signals terminating with logic '10' and units 28' and 58' to signals terminating with logic '11'.

It will be appreciated that a greater number of regenerators may be included in the system just described by expanding the addressing byte (the latter two bits) of the interrogation code.

However, increasing the number of regenerators between stations increases the interrogation period.

It will also be realised that the number of regenerators included between stations may be iess than four in each direction simply by programming the intermediate station to expect no response from a particular interrogation.

With each intermediate station 5 interrogating a respective eight supervisory units the procedure outlined above takes approximately 750 milli-seconds and referring also to Fig. 4 occurs in the time scale marked local interrogation.

On completion of the local interrogation the intermediate station which was defined by the latter coded bits of the original interrogate instruction from the terminal station 1 sends to the terminal stations 1 and 2 a series of signals relating to amplifying systems at the intermediate station and then forwards a series of signals giving detailed information on alarms or error signals received from its respective eight regenerator supervisory units.

The period of this reply is referred to in the timing diagram of Fig. 4 as "expanded dis play".

When the terminal station 1 has received the expanded display data it sends information indicating whether an alarm is present in its section and if so on which system and at which regenerator.

A similar compunded alarm report is then sent by each intermediate station in turn in both directions along the metallic pair 8 to the terminal stations 1 and 2.

When all of the intermediate stations 5 and 6 have sent their respective reports the terminal station 2 sends its compounded alarm report to the terminal station 1.

The expanded display referred to above may be sent by one or other of the terminal stations 1 and 2 if required.

The information received from the intermediate stations is used to drive displays on the display panels 3 at each of the terminal stations 1 and 2.

The displays each include a first set of four light emitting diodes, one per optical fibre 4, which are respectively illuminated if an alarm has been raised anywhere in the system affecting a respective optical fibre 4. A second set of light emitting diodes, one per terminal station and one per intermediate station indicate at which station or stations the alarm shown on the first set of light emitting diodes has occurred. The optical fibre to which the second set of light emitting diodes relate may be selected by manually operable means.

A third set of light emitting diodes show the expanded display referred to above and the station to which this relates may also be selected by manually operable means.

Either of the terminal stations 1, 2 may be used as the control station and the expanded display or system fault display may be selected from either station.

It will be realised that whilst the system as hereinbefore described uses a current source the signalling method and sequence will function in a similar manner when power is fed from a constant voltage source.

Claims

1. A signal transmission system comprising first and second terminal stations, an intermediate station between the first terminal station and the second terminal station, and a plurality of regenerators between the first terminal station and the intermediate station and/or between the intermediate station and the second terminal station, the intermediate station including means for receiving and storing error or alarm signals from at least some of the plurality of regenerators and means to transmit data relating to the error or alarm signals on demand from one of the terminal stations for subsequent analysis.

2. A signal transmission system according to Claim 1 including a plurality of intermediate stations and a plurality of regenerators between at least one pair of adjacent intermediate stations, each intermediate station which has associated regenerators having respective means for receiving and storing error or alarm signals from a respective plurality of the plurality of regenerators and respective means to transmit data relating to the error or alarm signals on demand from one of the terminal stations.

3. A signal transmission system according to Claim 2 in which each intermediate station which has associated regenerators is arranged to receive and store error or alarm signals from a respective plurality of regenerators on each side of that intermediate station.

4. A signal transmission system according to Claim 3 in which each intermediate station which has associated regenerators is arranged to interrogate each of its respective regenerators on one side thereof in turn on a first instruction from one of the terminal stations and to interrogate each of its respective regenerators on the other side thereof in turn on a further instruction from one of the terminal stations.

5. A signal transmission system according to Claim 2 or Claim 3 in which each intermediate station which has associated regenerators is arranged to interrogate in turn each of its respective plurality of regenerators on an instruction from one of the terminal stations.

6. A signal transmission system according to Claim 4 or Claim 5 in which each of the intermediate stations which has associated regenerators is arranged to interrogate its respective regenerators on one side at the same time as each of the other intermediate stations interrogate their respective regenerators on the same side and each of the intermediate stations is arranged to interrogate its respective regenerators on the other side at the same time as each of the other intermediate stations interrogate their respective regenerators on the other side.

7. A signal transmission system according to any preceding Claim in which each terminal station includes means for receiving and storing error or alarm signals from a respective plurality of regenerators and means to transmit data relating to the error or alarm signals so received on demand from the other terminal station.

8. A signal transmission system according to Claim 7 in which each terminal station is arranged when demanding data from the intermediate station(s) and the other terminal station to transmit to the other terminal station data relating to the error or alarm signals received from its associated regenerators.

9. A signal transmission system according to any preceding Claim in which the or each intermediate station is capable of receiving error or alarm signals from up to four regenerators on each side.

10. A signal transmission system according to any preceding Claim in which the transmission medium is an optical fibre or a plurality of optical fibres.

11. A signal transmission system according to any preceding Claim in which each regenerator is arranged to assemble its respective error or alarm signals into a multi-digit signal unit and is arranged to transmit each digit of the signal unit at one of two frequencies one of the frequencies representing a '1' digit and the other representing a '0' digit.

1 2. A signal transmission system according to Claim 11 in which said frequency representing a '1' digit is 1300 Hz.

1 3. A signal transmission system according to Claim 11 or Claim 1 2 in which said frequency representing a '0' digit is 1 700 Hz.

1 4. A signal transmission system according to any preceding Claim in which the or each intermediate station is arranged to assemble a multi-digit signal unit representing the error or alarm signals received from its respective associated regenerators and said means to transmit data relating to the error or alarm signals is arranged to transmit each digit of the signal unit at one of two frequencies, one of the frequencies representing a '1' digit and the other representing a '0' digit.

1 5. A signal transmission system according to Claim 14 in which said frequency representing a '1' digit is 390 Hz.

1 6. A signal transmission system according to Claim 14 or Claim 1 5 in which said frequency representing a '0' digit is 450 Hz.

1 7. A signal transmission system substantially as hereinbefore described with reference to the accompanying drawings.