JPS6161303B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention arranges a plurality of stations having a data drop/add function along a loop-shaped optical transmission line, and communicates between these stations in a time-division manner via the optical transmission line. It relates to an optical loop data transmission method that enables

The idea behind the loop data transmission method, in which multiple stations are placed along a loop-shaped transmission path, is as follows.
In 1970, Edgar H. Steward organized the
Internationdl Conference on Communications
“A LOOP TRANSMISSION” announced at
It was first clarified in a paper entitled ``SYSTEM''.The basic idea is that it aims to efficiently use a loop-shaped transmission line with a time division multiplex configuration among many users. Each station has a regeneration/relay function for pulses passing through the transmission line, a synchronization function, and a data drop/add function.

Conventionally, in such loop data transmission systems, twisted pairs or coaxial lines used in telephone transmission have often been used as transmission media. In particular, twisted wire pairs, which are simply a pair of twisted copper wires, have been proven to have sufficient characteristics as a transmission medium for pulse transmission and have been widely used. However, in recent years, along with the development of semiconductor lasers and light-emitting diodes, the development of low-loss optical fibers has progressed, and optical fibers are extremely thin, lightweight, resistant to external noise, and suitable for resource conservation. It has emerged as an attractive transmission medium. As a result, a movement has emerged to use optical fiber as a transmission medium for loop data transmission systems.

There is no great technical difficulty in using optical fiber as a transmission medium for a loop data transmission method (hereinafter simply referred to as the loop method). In that case, the repeater provided in each station may be an optical repeater. However, there are some problems here. This is a problem with the reliability of the loop system, which also exists in conventional systems. In the loop system, if any one repeater on the loop fails, all users will be unable to communicate. For this reason, the conventional loop method is usually used in a duplex manner. Even when using optical fibers, reliability can be improved by duplicating the system.
However, in the case of conventional twisted pair wire systems, it is possible to supply power from a central station to remote stations using the same medium, but in the case of optical fiber, power cannot be supplied from the center unless a separate power supply line is installed. Therefore, each station usually prepares a local power supply, but naturally this local power supply is required to have high reliability. Additionally, the problem of remote monitoring arises because of the need to take measures such as turning on and off the power of stations that are located remotely during operation, and detecting and detouring stations where an abnormality has occurred.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the loop system using optical fibers as described above, and to provide a system in which a failure in the electrical system of a remote station is less likely to cause the entire system to stop functioning. In particular, in the field of optical fiber transmission, optical-related devices have made remarkable progress, and good optical branching and coupling circuits are being developed. Therefore, in this invention, the signal branching/coupling part in each station of the optical loop method is constructed with an optical branching/coupling circuit as much as possible, and one of the stations has a central Use it as a station. If it is unavoidable that the transmission loss of the optical transmission line exceeds a certain level, a regenerative repeating station with a regenerative repeating function for optical pulses is installed in addition to the central station. In addition to the above, the most important part of this invention is that when an optical pulse is coupled to a transmission line at a branching/coupling station using an optical branching/coupling circuit, the coupling of the optical pulse is transmitted to other users. The purpose is to take measures to prevent interference.

Hereinafter, the configuration of the present invention and its operating principle will be explained in detail with reference to the drawings. FIG. 1 shows an example of the configuration of a conventional loop system. In the figure, 1 is a central station, 2 and 3 are remote stations, and 4 is a loop-shaped transmission line. The central station 1 uses a time division multiplexing (demultiplexing) device 12 operated by a clock generated by a main oscillator 11 to perform predetermined communication of input data from a group of data input/output terminals 13 for users based on a predetermined frame structure. Insert into time slot. The output of the time division multiplexing/demultiplexing device is sent to the transmission line 4 through the line driving circuit 14. The signal flowing on the transmission line 4 is returned to the central station 1 via the remote stations 2 and 3. The returned signal is sent to the receiving circuit 1 provided at the receiving end of the central station.
5, the signal is reproduced as a signal waveform similar to the time division multiplexed signal waveform input to the line drive circuit 14 described above. In the receiving circuit 15, a timing wave necessary for signal reproduction is generated from the received signal and output together with the reproduced signal waveform. 16 is a write/read buffer, in which the signal from the loop transmission line is once stored, and then transferred to the time division multiplexing/demultiplexing device 12.
be taken in.

Reference numeral 21 in the remote station 2 is a pulse regeneration repeater circuit having an add/drop function, and 22 and 23 are the same as those in the central station 1, the receiving circuit 15, and the line driving circuit 14, respectively. Reference numeral 24 denotes a time-division multiplex signal coupling/demultiplexing device which outputs the time-division multiplex signals received from the central station through the receiving circuit 22 to the data input/output terminal group 25 for users accommodated in the remote station 2. Separate the signals. This device also has the function of inputting signals to be sent to other stations from a group of user terminals into the system at a predetermined time phase and sending them out to a transmission line through a logic gate provided in the pulse relay circuit 21. Although the time-division multiplexing signal coupling/demultiplexing device 24 needs to know in advance the predetermined time phase required for communication with other stations, further explanation will be omitted as this is a description of the prior art. Note that a large number of stations such as the remote station 2 are normally arranged on the loop transmission line 4. FIG. 1 shows, by way of example, two such remote stations.

Now, in order to replace the loop transmission line of the above conventional system with an optical transmission line, the connection part with the transmission line must be equipped with an optical/optical conversion function or vice versa.
It is thought that it is sufficient to simply add a circuit with an electrical conversion function. However, this is accompanied by the aforementioned difficulties. Although not shown in FIG. 1, if the transmission line is a conventional twisted wire pair, the remote stations can be powered from the central station through the twisted wire pair. On the other hand, in the case of the optical loop method, if power is supplied from the center, a separate power supply line is required, so it is common practice to secure power supply to remote stations locally. In such cases, a failure in the electrical system of one remote station can cause the entire loop to fail.
Therefore, it is desirable that the pulse regeneration repeater circuit of the remote station be constructed only of passive optical elements having a drop/drop function as much as possible.

As mentioned above, the purpose of this invention is to overcome the problems that occur when realizing the pulse regeneration repeater part of a remote station using passive optical branching and coupling elements, and to provide a highly reliable optical loop system. I have something to do.

One of the problems is related to optical branching and coupling. Currently, there are various types of branching/coupling elements on the market that branch out a part of the optical signal passing through the main path, or conversely couple a local optical signal to the main path. In particular, the passage loss of the main path is considerably reduced to within 1 to 2 dB. However, as can be understood from the conventional configuration shown in FIG. 1, when local signals are combined, in the conventional electric circuit, the signal on the main path is temporarily interrupted by a logic gate. If we try to realize this using passive optical elements, the result will be as shown in Figure 2. In the figure, 31 and 32 are optical branching circuits and coupling circuits.
33 and 34 are optical gate circuits, which normally operate complementary to each other based on electrical signals. That is, the loop signal normally enters from the input end A of the optical branching circuit 31, and a part of it is output to the branching end D, but most of it passes through the main path M and the gate circuit 33, and is sent to the optical coupling circuit. appears at output terminal B of 32. At this time, the gate circuit 33 is open and allows the signal to pass through, while the gate circuit 34 is closed and blocks the signal from the local signal input terminal C from passing through. When you want to combine local signals, close the gate circuit 33,
Open the gate circuit 34. Of course, the gate circuit 34
can be omitted by controlling the local signal source. Such gate circuits require optical switches that operate in response to electrical control signals.
Currently, there are only those that operate mechanically at low speeds, and those that require high voltage control signals of several hundred volts even at high speeds, making it nearly impossible to use them for data loop applications. Therefore, the present invention aims to provide a loop system using a branching and coupling circuit from FIG. 2 except for the gate circuit. For this reason, it is necessary to ensure that no optical signals are flowing through the main path during the time phase in which the remote station combines the signals, but this will be discussed later.

Another problem concerns the level of light coupling. That is, the optical signal attenuates as it passes through a number of remote stations along the loop. Therefore, if the level of optical coupling from each remote station to the optical loop is the same, the magnitude of the pulses on the optical loop will be inconsistent. Depending on the transmission path loss, the unevenness of the amplitudes of the optical pulses can lead to a difference of 10 times or more in some cases. This means that if the pulse reproduction threshold on the receiving side is adjusted to the smallest pulse, the threshold will not be optimal for large pulses, making it vulnerable to interference noise. Interference noise arises from the waveform response of one pulse influencing other pulses while passing through a transmission path. This interference noise occurs even when large pulses interfere with each other.
Furthermore, even in the case of interference from a large pulse to a small pulse, using a non-optimal threshold as described above will cause reproduction errors. Therefore, another aim of the present invention is to provide a system in which the irregularity of optical pulses is minimized as much as possible.

The configuration and operating principle of the present invention will be described below with reference to the drawings.

FIG. 3 shows an embodiment of the optical loop data transmission system of the present invention. This embodiment consists of one central station 41 and two remote stations 42 and 43, similar to the configuration of FIG. 1, except that the loop-shaped transmission line 44 is an optical loop. Therefore, the line drive circuit 54 of the central station 41 has a function of converting an electrical signal into an optical signal, and the receiving circuit 55 has a function of converting an optical signal into an electric signal. 14 and receiving circuit 15. However, light
Since known circuit technology can be used for electrical conversion and inverse conversion, a detailed explanation of the circuit will be omitted. Also the third
Reference numerals 51, 53, and 56 in the figure represent a main oscillator, a data input/output terminal group, and a write/read buffer, respectively, and correspond to 11, 13, and 16 in FIG. 1, respectively. Reference numeral 52 in FIG. 3 is a time division multiplexing/demultiplexing device, which corresponds to 12 in FIG. 1, but there are some differences in functionality. This will be discussed later.

The remote station 42 is an optical branching and coupling circuit 6.
1. Optical receiving circuit 62, optical line driving circuit 63,
It consists of a time division multiplexing/demultiplexing device 64 and a group of user data input/output terminals 65. Optical branching and coupling circuit 6
1 can be realized in principle with the configuration shown in FIG. 4, in which two optical branch circuits 32 shown in FIG. 2 are connected back to back. That is, the optical branching/coupling circuit shown in FIG. 4 consists of an optical branching circuit 610 and an optical coupling circuit 511. Since the branching coefficient of an optical branching circuit is equal to the coupling coefficient when the circuit is used as a coupling circuit, generally the coupling coefficients are changed between the branching circuit 610 and the coupling circuit 611. For changing the coupling coefficient of branch circuit 610 for each remote station, see F.
Aurache and HHWitte et al. in Applied Optics in 1977
“Optimized layout for a” published in the December issue of
data bus syetem based on a new planar
However, the coupling coefficient has not yet been reported. In this invention, the intensity of the optical pulse coupled to the optical loop transmission line by the optical coupling circuit is measured by the coupling circuit. Make the intensity equal to the intensity of the optical pulse passing through the main path, so that a series of optical pulses with a constant intensity always appears on the output side of the optical coupling circuit.In order to do this, in addition to determining the coupling coefficient of the optical coupling circuit, coupling It is necessary to determine the intensity of the optical pulse itself.One method is to keep the coupling coefficient of the optical coupling circuit constant and adjust the intensity of the coupled optical pulse by appropriate means.This will be explained below. Add explanation.

The line drive circuit 63 in FIG. 3 includes the above-mentioned optical pulse intensity adjustment function, and a specific example of its configuration is shown in FIG. A light source 63 realized by a light source drive circuit 630, a laser diode, etc.
1. Optical attenuator 632 and optical branch circuit 633
are connected in series. The light source 631 is modulated by the output signal X of the light source drive circuit 630 which receives the timing signal T and the data signal S as input.
The modulated optical signal passes through an attenuator 632 and a branch circuit 633 to become a coupled signal Y to the loop. The other output Z of the branch circuit is for monitoring. The amount of attenuation of the attenuator 632 is manually changed based on the monitor output Z and the receiving level of light from the receiving circuit 62 shown in FIG. 3, and adjusted to a desired output level. Note that the output of the attenuator 632 can also be used for level adjustment,
In that case, the branch circuit 633 becomes unnecessary, but in actual devices, it is often convenient to have the monitor signal Z. Furthermore, although the level adjustment using the attenuator 632 has been described above, in the case of a light source such as a laser diode, adjustment can be made to some extent by changing the DC bias of the diode. Here, since the adjusting means itself is not a subject of the invention, further explanation will be omitted.

Time division multiplex signal combiner/demultiplexer 64 in remote station 42 of FIG. 3 corresponds to 24 of FIG. 1, but with some functional differences. This device 64 is connected to the time division multiplexing and demultiplexing device 52 in the central station 41.
The operating principles of both devices will be explained in detail below.

FIG. 6a shows a time division multiplexing/demultiplexing device 5 of the present invention.
2 shows an example of a frame structure of a multiplexed signal transmitted by No. 2. There is usually a frame synchronization pulse F in one frame. This pulse may consist of a single bit or multiple bits may be used. A control data channel CD is provided next to the synchronization pulse F to send control data. Then there is a channel that inserts data between stations.
CH ₁ , CH ₂ , ...CHn are provided. The control data includes, for example, channel assignment information indicating which channel communication between stations is to be made, online monitoring information for monitoring whether each station is operating normally during operation, and the like.

Now, in the loop system of the present invention, the branching and coupling circuit of the remote station is passive as described above, so in order for the remote station to couple information to the loop, the time slot to be coupled must be set at the central station. It needs to be in an empty state. This time slot to be combined, or the "empty state" of the channel, is realized by clearing the channel to, for example, "all zeros" at the central station, so that no optical signal is sent to the output of the line drive circuit 54. Ru. Now, a user U ₁ at the first remote station 42
It _is assumed _{that data is exchanged with a user U 2 at a remote} station ₄₃ of Assume that the transfer is already given to use CH ₂ .
At this time, optical signals are combined at the first remote station 42 at the CH ₁ position in the frame, and the combined signals are transmitted to the second remote station 43 along the loop. Meanwhile, CH ₂ in the frame
The optical signal is combined at the second remote station 43, and the combined signal passes along the loop through the central station to the first remote station. However, the problem here is that
The optical signal sent from the central station is CH ₁ and
If it is not cleared at the CH ₂ location, the remote station will not be able to successfully combine the optical signal, whereas if this is done at the central station, the signal of user U ₂ using CH ₂ will not be transmitted to user U ₁ . This is the point where it disappears.

Therefore, in the present invention, the signal combined at the CH ₂ position is transferred to another free channel, for example, CH ₃ , in the central station (that is, the time slots are swapped), and then CH ₂ is cleared. User U ₁ at the first remote station will receive data from user U ₂ over CH ₃ . Such swapping of time slots is only necessary when remote stations communicate with each other, in which case a pair of users will use three channels. On the other hand, between the central station and the remote station, no swapping of time slots is necessary, and a pair of users will use two channels. Therefore, from the point of view of channel utilization efficiency, it can be seen that the method of the present invention is more effective when the remote stations communicate more with the central station than with each other.

FIG. 6b corresponds to the above example and is a conceptual diagram of the optical signal strength sent from the central station to the loop,
CH ₁ and CH ₂ are cleared, and a signal to user U ₁ to which user U ₂ has joined the loop through CH ₂ is inserted into CH ₃ by time slot swapping. Further, FIG. _1c is a conceptual diagram showing the intensity of the optical signal passing through the remote station 42,
The optical signal is coupled from user U ₁ to user U ₂ at the location. Further, the intensity of the combined optical signal at this time is adjusted to the same level as other parts within the frame. Similarly, FIG. 6d is a conceptual diagram showing the intensity of the optical signal passing through the remote station 43, in which the optical signal from user 2 to user 1 is coupled to CH ₂ .

FIG. 7 shows a specific example of the configuration of the central station 41 of the optical loop data transmission system of the present invention. As mentioned above, the central station 1 has a main oscillator 51,
Time division multiplexing and demultiplexing circuit 5 driven by this
2. The main components are a user data input/output terminal group 53, a line driving circuit 54, a receiving circuit 55, and a write/read buffer 56.

Master oscillator 51 generates a timing signal equal to the data pulse repetition frequency flowing on the loop. The main functions of the time division multiplexing and demultiplexing circuit 52 are (i) generation of frame structure, (ii) data input from the user, and (iii)
(iv) exchanging time slots, (iii) (v) buffering of received data necessary for execution of (iv), (vi) frame alignment, etc.

The frame structure is generated as follows. First, the frame pulse generator 100 divides the frequency of the timing signal generated by the oscillator 51 to generate a frame pulse that provides a frame period. A part of the frame pulse and timing signal is input to the frame synchronization pattern generator 101 and converted into the frame synchronization pulse F described above. Further, the frame pulse and other part of the timing signal are applied to the channel counter 102 and the main control section 103. Channel counter 102 generates a channel designation signal indicating which channel time slot the current time corresponds to, depending on the time within the frame starting with the frame pulse. The channel designation signal includes a plurality of binary signals that address the memory, which will be described later, and one write/read timing signal that gives an instruction to write or read from the memory. The main control unit 103 also generates the control data signal for the control data channel CD as one of its outputs. In addition,
The illustrated thin lines represent one type of signal line, and the thick lines represent multiple signal lines.

Only the data from the channel specified by the input/output channel designation signal 105 of the main control unit 103 is coupled to the input bus line 106, and the data from the user is connected to the first input bus line 106 by an appropriate input timing pulse generated by the main control unit 103. Written to parallel/serial converter 107. At this time, gate 108 is closed. Immediately after data is written into the first parallel/serial converter 107, the data is shifted to the right by a timing signal and output as serial data. At this time, the main control unit 103 controls the gate 1
08 is opened and this serial data is passed through. When all data to be transferred has been output, gate 108 is closed again. The frame synchronization pulse F of the frame synchronization pattern generator 101 mentioned above, the control data signal generated by the main control section, and the output of the gate 108 are combined by an OR gate 104 to form a signal in FIG. 6a.
A pulse train having the frame configuration shown in FIG. 1 appears on the output side of the OR gate 104.

Next, data reception from the loop transmission path will be explained. The optical signal sent through the loop transmission path is passed through the input terminal 200 to the photoelectric conversion element 201.
is transmitted and converted into an electrical signal. The well-known Avalanche photoelectric conversion element 201
A photodiode or the like can be used. The received signal processing circuit 202 reproduces the received timing signal and data sequence from the electrical received signal obtained from the photoelectric conversion element 201 by performing shaping processing or the like. Although the reception timing signal has the same pulse repetition frequency as the timing signal generated by the main oscillator 51, it is generally extracted through nonlinear processing of the reception signal, so it is accompanied by phase jitter.
If variations in transmission path delay or the phase jitter described above are not a problem, the timing signal of the main oscillator can be used instead of the reception timing signal. The general configuration of the received signal processing circuit belongs to a known technique and is not directly related to the gist of the present invention, so a description thereof will be omitted.

Now, since the reproduced data series is generally affected by delay fluctuations in the transmission path, this effect is absorbed by the write/read buffer 56. That is, the reproduced data series is read out in order of arrival (First-In First-Out Buffer) 20.
3 is temporarily stored. The write pulse of the arrival order readout circuit 203 is obtained by passing the above-mentioned reception timing signal through the gate 204, and the read pulse is obtained by passing the timing signal of the output of the main oscillator 51 through the gate 205. The gates 204 and 205 are open during normal operation, but when the arrival order readout circuit is empty or full, such as when the system is started up, a signal is sent to the arrival order readout circuit 2 to notify this fact.
03 to the control circuit 206, and the control circuit 2
06 operates and gate 204 or gate 20
5 is closed for a certain period of time. Note that the minimum required capacity of the arrival order readout circuit 203 varies depending on the loop length, but in terms of design, it may be adjusted to the delay variation with respect to the applicable maximum loop length.

The output of the arrival order reading circuit 203 is sent to the frame alignment section 11 in the time division multiplexing/demultiplexing circuit 52.
0 can be communicated. Frame alignment section 11
0 is frame synchronization circuit 111, phase comparison circuit 11
2. Consists of a variable delay circuit 113 and a serial/parallel conversion circuit 114. The frame synchronization circuit 111 captures the synchronization pattern sequence generated by the frame synchronization pattern generator 101 sent through the loop transmission path, and generates a frame pulse indicating the synchronization pulse position in the received data sequence. This frame pulse has the same period as the frame pulse generated by the frame pulse generator 100, but generally has a different phase relationship. Therefore, the phase comparison circuit 112
The phase difference between both frame pulses is calculated by the main oscillator 5.
1 is generated, and the result is transmitted to the variable delay circuit 113. A part of the output of the arrival order reading circuit 203 is transmitted to the variable delay circuit 11.
3 and are sequentially written into the serial/parallel conversion circuit 114 after receiving a necessary delay. The output data series sent out from the OR gate 104 and the received data series returned to the central station via the loop transmission line and output from the arrival order readout circuit 203 are operated by the same timing signal generated by the main oscillator 51. Therefore, the phase difference between the frames of both data series is constant during normal operation. Therefore, the phase difference information output by the phase comparator circuit 112 remains constant during normal operation. When the delay amount of the variable delay circuit 113 is appropriately set based on this phase difference information, the contents of the serial/parallel conversion circuit 114 are transferred to the first frame memory 120 by a write/read signal which is one of the outputs of the channel counter 102. Alternatively, it becomes possible to write correctly into the second frame memory.

Next, the time slot replacement function will be explained. In order to realize this function, it is easiest to use two frame memories. One of the two time slots is used for writing and the other for reading, and their functions are exchanged every frame. That is, it is selected which of the two frame memories to write to and which to read from by the output of the flip-flop circuit 122 whose state is inverted by the frame pulse. The result is the same whether changing the time slots is controlled by writing or by reading. FIG. 7 shows an example of control by reading. In the figure, the channel designation signal and the write/read signal, which are the outputs of the channel counter 102, are transferred to the frame memory 120 by a first switching circuit 123.
(or the frame memory 121), and the contents of the serial/parallel converter 114 are transferred to the frame memory 121.
0 (or frame memory 121) at the location addressed by the channel designation signal. A part of the channel designation signal is also transmitted to the channel allocation storage circuit 124, where it undergoes read address conversion necessary for time slot replacement. If the time slots do not need to be replaced, the channel designation signal is output as is without being converted. The output of the channel allocation storage circuit 124 is transmitted by the second switching circuit 125 to the frame memory 121 (or frame memory 120) to which no writing is being performed, and the contents of the designated address position in the frame memory are read out.
As described above, the relationship between writing and reading is switched every frame. The signal read from the frame memory is sent to the second parallel-to-serial conversion circuit 126.
At the same time, it is taken out as it is to the user input/output terminal group 53, and is passed to the user side based on the input/output channel designation signal 105 and a predetermined timing. The details of the input/output interface will be omitted since they are not directly related to the gist of this invention. Immediately after writing, the contents of the parallel-to-serial conversion circuit 126 are sequentially shifted to the right according to the timing signal output from the main oscillator 51 and output as serial data. multiplexed inside. The gate 127 is closed at the channel position to be set and opened at other times under the control of the main control section 103.

As explained above, the time slots are replaced by changing the read address of the frame memory, but it is assumed that the contents of the change are stored in the channel allocation storage circuit 124. If it is not necessary to change the channel allocation during the operation period, the channel allocation storage circuit 124 can be implemented as a patch board type matrix circuit that allows manual address correction, and the patch can be redone when necessary. If the channel assignment is to be changed frequently, the channel assignment memory circuit 124 should be replaced with RAM (random access memory).
It is desirable to adopt a method in which the information is configured as follows and is rewritten by a command from the main control unit 103. Changes in this case must be made through information exchange with the remote station, but there are various known techniques for this, and since they are not directly related to the gist of the present invention, further detailed explanation will be omitted.

Note that the multiplexed output data series obtained in the above manner is given to the line driving circuit 54 together with a timing signal, converted into an optical signal, and sent out to the loop transmission line. The light source drive circuit 207 in the line drive circuit 54 outputs the output in the time division multiplex ratio demultiplexer 52.
This is an electric circuit that includes a function of shaping the output of the OR gate 104 and a function of supplying a bias current necessary for driving the light source 208. Also light source 2
As 08, it is possible to use an LED (light emitting diode) or LD (laser diode).

The general structure of the remote station of this invention has already been explained in connection with FIG.
Optical branching and coupling circuit 61 and optical line drive circuit 6
3 has already been described in detail. Further, the optical receiving circuit 62 has the same configuration as 55 in FIG. Therefore, the remaining portion, the time division multiplex signal coupling/demultiplexing device 64, will be explained below.

FIG. 8 shows a specific example of the configuration of the time division multiplex signal coupling/demultiplexing device 64 used in the remote station 42 of the optical loop data transmission system of the present invention. In the figure, 40 and 641 are input terminals that receive a timing signal and a reproduced data signal from the optical receiving circuit 62, respectively. The reproduced data signal is applied to a frame synchronization circuit 642, which detects a frame position in the data signal in the same way as the frame synchronization circuit 111 of FIG. 7, and generates a frame pulse indicating this position. The other part of the data signal is applied to the serial/parallel conversion circuit 643 and given to the user side through an output pulse 646 together with an input/output channel designation signal 645 from the main control section 644. Further, the coupled signal from the user to the loop transmission path is written to the parallel-to-serial conversion circuit 648 via the input bus 647 by a timing pulse from the main control unit 644, and then shifted to the right by the timing signal mentioned above and outputted through the gate 649. be done. Output terminal 650 is the output terminal for the data signal to be coupled to the loop transmission line, and this signal corresponds to signal S in FIG. Further, another output terminal 651 is a terminal for outputting the timing signal received through the input terminal 640, and this signal corresponds to the signal T in FIG. In order for the main control unit 644 to output an appropriate control signal, it is necessary to receive the frame pulse described above from the frame synchronization circuit 642, but in addition to this, it is necessary to determine which channel is assigned to which of the user input/output terminals of this remote station. allocation information is required. It is assumed that this information is stored in the channel allocation storage circuit 652 as in the case of the central station. As in the case of the time-division multiplexing ratio demultiplexing device 52 of the central station in FIG. Main control section 6
44 will use it.

As can be seen from the above explanation, the time-division multiplexing signal combining and demultiplexing device 64 at the remote station is the time-division multiplexing ratio demultiplexing device 5 at the central station shown in FIG.
2, it can be said that the frame alignment function, the time slot switching function by the write/read frame memory, or the clearing function of unnecessary channels by the gate 127 operating in communication with the main control section 103 are removed. Finally, although the above description relates to one embodiment of the optical loop transmission system of the present invention shown in FIG. 3, other implementations are possible. For example, in addition to the central station, there may be several regenerative repeating remote stations that have a complete regenerative repeating function for optical pulse sequences like the central station, and further between the central station or regenerative repeating remote stations. It is conceivable to arrange a remote station that does not have the above-mentioned regenerative relay function. In this regenerative relay type remote station, the receiving circuit 22 and line driving circuit 23 of the remote station 2 shown in FIG. 1 may each include an optical-to-electric conversion function and an electric-to-optical conversion function. Needless to say, in this case, reliability maintenance of the regenerative relay type remote station becomes a problem.

As described above, by using the optical loop data transmission method of the present invention, a highly reliable system can be provided that can avoid complete system stoppage due to electrical failure at a remote station. Another advantage is that if only the optical branching and coupling circuits are placed remotely in advance, it becomes possible to change the location of the remote station without stopping operation.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the configuration of a conventional loop system, where 1 is a central station, 2 and 3 are remote stations, 4 is a loop-shaped transmission line, 11 is a main oscillator, and 12 is a time division multiplexing/demultiplexing device. , 13 and 25 are data input/output terminal groups, 14 and 23
is a line driving circuit, 15 and 22 are receiving circuits, 1
6 is a write/read buffer, 21 is a pulse relay circuit, and 24 is a time division multiplex signal coupling/separation device. Fig. 2 is an explanatory diagram of the conventional pulse repeater circuit when it is realized by an optical element, and 31 is an optical branch circuit;
32 is an optical coupling circuit, and 33 and 34 are gate circuits. FIG. 3 is a diagram for explaining an embodiment of the optical loop data transmission system of the present invention, in which 41 is a central station, 42 and 43 are remote stations,
44 is an optical loop transmission line, 51 is a main oscillator, 5
2 is a time division multiplexing ratio demultiplexing device; 53 and 65 are data input/output terminal groups; 54 is an optical line driving circuit;
5 and 62 are optical receiving circuits, 56 is a write/read buffer, 61 is an optical branching/coupling circuit, and 63
is a line drive circuit including a light level adjustment function, 6
4 is a time division multiplex signal combination/separation device. FIG. 4 is an explanatory diagram of the optical branching and coupling circuit used in the embodiment of the present invention, and FIG. 5 is a line drive circuit 6 including a light level adjustment function used in the embodiment of the present invention.
630 is a diagram for explaining a specific configuration example of No. 3.
631 is a light source, 632 is an attenuator, and 633 is a branch circuit. FIG. 6 is a diagram for explaining the operation of the optical loop data transmission system of the present invention, in which a is an example of the frame structure of a multiplexed signal, and b is the intensity of the optical signal sent from the central station to the optical loop transmission line. conceptual diagram, c and d are remote station 42, respectively.
and 43 is a conceptual diagram showing the intensity of the optical signal that has passed through the filters 43 and 43. FIG. 7 is a diagram showing a specific configuration example of the central station 41 of the optical loop data transmission system of the present invention, in which 100 is a frame pulse generator, 101 is a frame synchronization pattern generator, 102 is a channel counter, and 103 is a main control. 104 is an output OR gate, 105 is an input/output channel designation signal, 10
6 is an input bus line, 107 is a first parallel-serial converter, 110 is a frame alignment section, 11
1 is a frame synchronization circuit, 112 is a phase comparison circuit,
113 is a variable delay circuit, 114 is a serial-parallel conversion circuit, 120 and 121 are frame memories, 122 is a flip-flop, 123 and 125 are switching circuits, 124 is a channel allocation storage circuit, 126 is a second parallel-serial conversion circuit, and 201 is a A photoelectric conversion element, 202 a received signal processing circuit, 203 an arrival order readout circuit, 206 a control circuit, 207 a light source drive circuit, and 208 a light source. FIG. 8 is a diagram illustrating a specific configuration example of the time division multiplex signal coupling/demultiplexing device 64 used in the remote station 42 of the optical loop data transmission system of the present invention, in which 640 is a timing signal input terminal, and 641 is a data signal input terminal. terminal, 642 is a frame synchronization circuit, 643 is a serial-parallel conversion circuit, 644 is a main control section, 645 is an input/output channel designation signal, 646
is an output pulse, 647 is an input bus, 648 is a parallel-to-serial conversion circuit, 650 is a data output terminal, 651
652 is a timing signal output terminal, 652 is a channel allocation storage circuit, and 653 is a channel counter.

Claims (1)

[Claims] 1. In an optical loop data transmission system in which multiple stations with data add/drop functions are arranged along a loop-shaped optical transmission line, and communication between these stations is made time-divisionally possible via the optical transmission line. , at least one of the plurality of stations mentioned above is a regenerative repeating station that has a function of regenerating and repeating the pulse train flowing through the optical transmission line in addition to the function of adding and dropping data, and the other stations are inserted into the optical transmission line. The station is a branching/coupling station that sends and receives signals to and from an optical transmission line via a directional branching/coupling device, and at least one of the regenerative repeating stations has a loop-shaped optical function in addition to the regenerative repeating function. There is a function to give a time division multiplex frame structure to the pulse train flowing through the transmission path, a function to change the time slots according to the necessity of communication, and a function to clear the time slots that have already communicated and to clear the time slots that have not yet been communicated. This includes a function for clearing and transmitting after replacing the time slot of the target destination, allowing each branch/coupling type station to couple communication data to the optical transmission line through a predetermined cleared time slot, and for each branch/coupling station to The station is equipped with an optical pulse sending means that sends out optical pulses to the transmission line only in time slots where communication is permitted.
Intensity adjusting means for making the intensity of the optical pulse to be transmitted by the optical pulse sending means equal to the intensity of the optical pulse passing through the directional coupler of the branching/coupling station, depending on the position of the loop-shaped optical transmission line. An optical loop data transmission method characterized by comprising: