JPH05235977A - Optical communication system - Google Patents

Abstract

PURPOSE:To inform the occurrence of a fault in a node to all remaining nodes. CONSTITUTION:Plural nodes N1, N2,... Ni,... are coupled via an optical fiber 21 and an optical star coupler 20. Each node Ni is provided with a reception section 4 converting optical data from the optical fiber 21 into an electric signal and a transmission section 5 sending the optical data to the optical fiber 21. The data from the reception section 4 are given to a control section 6. The control section 6 controls the operation of the transmission section 5 to control the transmission of the optical data. The transmission section 5 sends usual data in a 1st luminous quantity being a comparatively small luminous quantity and error data in a 2nd luminous quantity being a comparatively large luminous quantity under the control of the control section 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system such as an optical LAN (local area network) in which a plurality of nodes are connected by a star connection system or a bus connection system.

[0002]

2. Description of the Related Art In an optical communication system in which a plurality of nodes are coupled by a star connection method, an optical fiber for optical data transmission / reception extending from each node is connected to an optical star coupler, and each optical fiber is connected via the optical star coupler. The node is connected to all remaining nodes. Further, in an optical communication system in which a plurality of nodes are connected by a bus connection method, an optical fiber cable forming a bus is provided with an optical connector, and the optical fiber connected to each node is coupled to this optical connector. The optical star coupler and the bus are shared by all the nodes, but the unique part of each node other than this shared part is called an optical link. That is, the optical link includes an optical fiber connected to an optical star coupler or a bus, a receiving unit including a photoelectric converter for converting light from the optical fiber into an electric signal and an amplifier for amplifying an output of the photoelectric converter, and It has a transmitter including a light emitting diode or the like that generates modulated light corresponding to the data to be transmitted.

The circuit configuration of the receiving unit of this optical link is roughly classified into two types, a direct current coupling system and an alternating current coupling system. The DC coupling method is a receiving circuit method applied when data is transmitted by the DC component of the amount of light.It generates a DC voltage corresponding to the amount of received light, and binarizes this DC voltage with an appropriate threshold value. Data is received by determining the data. The amount of received light varies depending on the node that performs data transmission due to the coupling loss between the optical fiber and the light emitting diode in each link, the variation in transmission loss in the optical fiber, and the variation in coupling loss in the optical star coupler. This variation in the amount of received light causes distortion in the pulse width after binarizing the output of the amplifier.
Therefore, in general, ATC (Automatic Threshold Co
(ntrol) circuit automatically changes the threshold value for binarization according to the amount of received light, and the AGC (automatic gain control) circuit changes the gain of the amplifier according to the amount of received light. The reception performance is improved by restoring a small digital signal.

On the other hand, the AC coupling system is a system adopted when transmitting coded data modulated within a predetermined frequency band. In this system, since it is not necessary to regenerate the DC component corresponding to the magnitude of the received light amount, a coupling capacitor is inserted between the photoelectric converter and the amplifier, for example. The frequency band of encoded data is limited by the capacitance of the coupling capacitor and the input impedance.

By the way, in a telecommunication system for transmitting data by an electric signal through a communication line, a jam area of several bits for detecting the presence or absence of a failure such as a reception error in a frame which is a unit of transmission data. Is provided. For example, in a telecommunication system in which a plurality of nodes are connected by a bus connection method, when an abnormality occurs in a certain node, this node sends a jam signal to the bus during the jam area. As a result, all the remaining nodes are notified that an abnormality has occurred in the node. After checking whether or not a jam signal is received in the jam area, each node shifts to processing such as transmission of data of the next frame and abnormal processing.

Such a communication system is preferably applied to an optical communication system, and it is expected that the reliability of data communication will be improved by this.

[0007]

However, in any of the above-mentioned conventional techniques in which the DC coupling method or the AC coupling method is applied to the receiving unit of the optical link, the amount of light received from the node corresponding to the frame immediately before the jam area is in all cases. When there is a lot of noise, there is a problem that jam signals from other nodes are poorly received. This problem will be described in more detail.

First, a configuration in which a DC coupling system using an ATC circuit is applied to the receiving section of the optical link will be described. AT
At the input section of the C circuit, peak hold of the input signal is performed. That is, the peak value of the input signal is held by the circuit having a constant time constant. For example, when the optical data from a certain node is received with a relatively large amount of light, the electrical level corresponding to this large amount of light is held for a recovery time corresponding to the time constant of the peak hold circuit. Therefore, if a jam signal with a small amount of light is received in a jam area following a frame received with a large amount of light, this jam signal may not be detected.

When the AGC circuit is used, the gain of the amplifier in the jam area is the gain corresponding to the node that transmitted the frame received immediately before the jam area. Therefore, when another node transmits a jam signal in the jam area, reception of the jam signal from this other node may become defective. In other words, the recovery time corresponding to the time constant of the circuit of the receiving unit is required until the gain corresponding to the other node is set, so that the appropriate gain cannot be set in the jam area for a very short time. However, there is a risk that the jam signal will be received poorly.

Further, when the AC coupling system is applied to the receiving section of the optical link, the circuit of the receiving section has a constant time constant because of the coupling capacitor and the like.
The same problem as in the case of the ATC circuit will occur. That is, the electrical holding level of the circuit of the receiving unit does not change immediately, and the holding level corresponding to the node that sent a frame corresponds to the node that sends a jam signal in the jam area following the frame. A certain recovery time is required to recover the holding level. As a result, the jam signal may be poorly received, and it may not be possible to notify all nodes of the abnormality of the node.

As described above, the above-mentioned conventional technique has a problem in that it is not possible to satisfactorily notify an abnormality occurring in a certain node to a plurality of nodes connected by the star connection method or the bus connection method. there were. Therefore, an object of the present invention is to solve the above-mentioned technical problem, and when an abnormality occurs in a certain node, this is surely performed in all the remaining nodes connected by the star connection method or the bus connection method. An object is to provide an optical communication system capable of making notification.

[0012]

In order to achieve the above object, the optical communication system according to claim 1 has a plurality of nodes connected by an optical transmission line in a star connection system or a bus connection system. In the optical communication system, each node includes a receiving unit for receiving optical data from the optical transmission line, and a first light amount or a second light amount larger than the first light amount.
With a light amount of, a transmission unit capable of sending optical data to the optical transmission line, an abnormality detection unit for detecting an abnormality in the node, and the transmission unit are controlled to perform normal transmission. The data is transmitted by the first light amount, and when the abnormality detecting unit detects an abnormality of the node, the transmission control unit transmits the abnormal data by the second light amount.

Optical data from each node is received by the other remaining nodes connected by the star connection method or the bus connection method via the optical transmission line. Focusing on a certain node, the light amount of the optical data received by the receiving unit of this node is different for each node that has transmitted the data. In other words, the attenuation due to the coupling loss between the optical transmission line and the transmission unit or the reception unit of each node or the attenuation due to the transmission loss in the optical transmission line varies from node to node, so the optical data received at a certain node The amount of light is different for each transmitting node.

According to the present invention, each node transmits optical data to the optical transmission line with a first light amount required to realize communication in a normal state and a second light amount larger than the first light amount. A transmitter is provided that can be sent to. And
Under the control of the transmission control means, when transmitting normal transmission data, the optical data is transmitted with the first light amount. On the other hand, the abnormality data transmitted when the abnormality detecting unit detects that an abnormality has occurred is transmitted to the optical transmission line with a second light amount, which is a large light amount.

Therefore, the abnormal data can be reliably received with a sufficient amount of light in the receiving units of all the nodes. Therefore, when an abnormality occurs in any of the nodes, it is possible to reliably notify all the remaining nodes of the abnormality. The optical communication system according to claim 2, wherein the transmitting unit supplies one light emitting element and a first current corresponding to the first light amount to the light emitting element.
Drive means and second drive means for causing a second current corresponding to the second light amount to flow through the light emitting element, and the transmission control section transmits the normal transmission data at the time of transmission. The first driving means is driven, the second driving means is driven when the abnormal data is transmitted, and further, the second driving means is driven in a pulsed manner at a predetermined duty ratio. It is characterized by including.

With this configuration, when abnormal data is transmitted,
The second drive unit is driven to generate optical data with the second light amount from the light emitting element. In this case, the second driving means is pulse-driven at a predetermined duty ratio.
Therefore, the second current corresponding to the second light amount flows in a pulsed manner in the light emitting element. Therefore, by setting the above duty ratio so that the time period during which the second current flows through the light emitting element is sufficiently short, even if this second current is larger than the maximum rated current of the light emitting element, The problem that the light emitting element is destroyed does not occur.

In this way, in order to generate optical data with a relatively large second light quantity, one light emitting element is used for the first light emitting element without using a light emitting element with a particularly high brightness. It is possible to achieve both the transmission of normal transmission data with the light amount and the transmission of abnormal data with the second light amount.

[0018]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 2 is a block diagram showing the overall configuration of the optical communication system according to the embodiment of the present invention. In this optical communication system, a plurality of nodes N1, N2, with an optical star coupler 20 as a center and an optical fiber 21 are used.
... are connected to each other by a star connection method to form a local area network. That is,
A certain node Ni (where i is a natural number) is coupled to all other remaining nodes Nk (where k is a natural number other than i) via the optical star coupler 20. .. In this embodiment, the optical star coupler 20 and the optical fiber 21 form an optical transmission line.

Each node Ni is optically coupled to the optical fiber 21 and a receiver 4 including a photoelectric converter for receiving light from the optical fiber 21, and optical data is coupled to the optical fiber 21 by optical coupling. And a control unit 6 electrically connected to the reception unit 4 and the transmission unit 5. The control unit 6 functions as an abnormality detection unit and a transmission control unit.

Data transmission between nodes is performed in units of frames each consisting of a predetermined amount of data, and a jam area, which is a period for detecting abnormality of a node, is provided between each frame. FIG. 1 is an electric circuit diagram showing the configuration of the transmission unit 5 of each node Ni. Three types of signals are given from the control unit 6. That is, a jam signal JAM indicating that the node is abnormal is given to the first input terminal T1, and an abnormality such as a reception error or an optical fiber disconnection occurs at the node to the second input terminal T2. The error detection signal ERROR indicating that is given, and the transmission data signal DATA corresponding to the transmission data is given to the third input terminal T3.

The waveform of each signal is shown in FIG. 3, and the jam signal JAM is a pulse signal with a constant duty ratio of 1 to n (n is a value of, for example, about 10), and an error detection signal. ERROR is a signal that is normally at a low level and remains at a high level for a fixed time ΔT when an abnormality is detected. The transmission data signal DATA is a pulse signal that has been modulated according to the transmission data. The time ΔT during which the error detection signal ERROR is at a high level is selected to be, for example, the time for a few pulses of the jam signal JAM. This is because there is a possibility that the pulse cannot be detected at the receiving side node with only one pulse, so there is a margin in order to reliably notify the abnormality. In the case of 10 Mbit / sec transmission, if the duty ratio of the jam signal JAM is 1:10, pulses of the jam signal JAM signal are generated every 1 μsec, so ΔT in this case is set to about 2 to 3 μsec. Would be preferred.

The jam signal JAM given to the first input terminal T1 is given to one input terminal of the NAND gate 11. An error detection signal ERROR is applied to the other input terminal of the NAND gate 11.
The error detection signal ERROR is also inverted by the inverter 13 and then applied to one input terminal of the other NAND gate 12. And this NAND gate 1
The transmission data signal DATA is applied to the other input terminal of 2. The outputs of the NAND gates 11 and 12 are input to the drive circuit 14 for driving the light emitting diode 15 optically coupled to the optical fiber 21.

The error detection signal ERROR from the second input terminal T2 is a control signal that gates the jam signal JAM and the transmission data signal DATA, and gives only one of the signals to the drive circuit 14. That is, if the error detection signal ERROR is at high level, an inverted signal of the jam signal JAM is derived from the NAND gate 11, and if the error detection signal ERROR is at low level, NAN is output.
An inverted signal of the transmission data signal DATA is derived from the D gate 12.

The drive circuit 14 has a pair of drive NPN transistors Q1 and Q2, and the signals from the NAND gates 11 and 12 are applied as control signals to the bases of the drive transistors Q1 and Q2. The collectors of the transistors Q1 and Q2 have resistors R1, R2; R3, respectively.
The power supply voltage Vcc is applied through R4. And
The voltage dividing point 16 of the resistors R1 and R2 and the voltage dividing point 17 of the resistors R3 and R4 are commonly connected to the light emitting diode 15 via the line 18.

For example, when the error detection signal ERROR is at low level, the output of the NAND gate 11 becomes high level and the transistor Q1 becomes conductive. In this case, if a low level signal is applied from the NAND gate 12 and the transistor Q2 is cut off, the current from the power supply flows from the resistors R1, R3 and R2 through the transistor Q1. At this time, the resistance R
The current flowing through R1 and R3 is relatively small, and these resistors R
Since the voltage drop at 1 and R3 is small, the potential of the line 18 is relatively high and the light emitting diode 15 becomes conductive. Therefore, the light emitting diode 15 is turned on by the current from the line 18. On the other hand, NAND
When a high-level signal is given from the gate 12 to turn on the transistor Q2, the current from the power source is generated by the resistor R1,
R3 and R2, R4 and transistors Q1, Q2
Flowing through. Therefore, the voltage drop across the resistors R1 and R3 becomes large, and the potential of the line 18 becomes relatively low.
As a result, the light emitting diode 15 is cut off.

When the error detection signal ERROR is at a high level, the transistors Q1 and Q2 are different from the above case.
The roles of will be changed. That is, in this case, the transistor Q2 is in the conductive state from beginning to end, the transistor Q1 is turned on / off in response to the signal from the NAND gate 11, and the light emitting diode 15 is turned on / off correspondingly. ..

In the drive circuit 14, the transistor Q1,
Assuming that the resistance values of the resistors R1, R2, R3, and R4 connected to Q2 are represented by these reference numerals, the relationship between the resistance values is set as follows, for example. R1 = R3 / n ··· (1) R2 = R4 / n ··· (2) However, “n” in the above formulas (1) and (2)
Is equal to the above-mentioned “n” that determines the duty ratio of the jam signal JAM.

As a result of the resistance value being set in this way, the light emitting diode 15 is turned off when the transistor Q1 is cut off.
The current flowing through the diode is approximately n times the current flowing through the light emitting diode 15 when the transistor Q2 is cut off. That is,
The light emitting diode 15 is driven to emit light with two types of light amounts, a first light amount L1 and a second light amount L2. As described above, the driving circuit 14 includes one light emitting diode 15
Two kinds of currents can be switched and flowed to the first and second driving means and correspond to the first driving means and the second driving means.

Next, the operation of the transmission section 5 will be described with reference to FIG. In FIG. 3, there are shown waveforms of signals derived to the respective parts of the configuration shown in FIG. 3 (a) shows the jam signal JAM, and FIG. 3 (b) shows the error detection signal ERRO.
R and FIG. 3 (c) respectively show the transmission data signal DATA, and the configuration of these signals is as described above. on the other hand,
The output signal of the NAND gate 11 is shown in FIG. 3 (d), and the output signal of the NAND gate 12 is shown in FIG. 3 (e). Further, in FIG. 3 (f), the light emitting diode 1
An emission level of 5 is shown.

The error detection signal ERROR is at a low level during the periods ΔT1 and ΔT3 during which the control unit 5 (see FIG. 2) does not detect the abnormality of the node. At this time, NA
Since the output signal of the ND gate 11 is fixed to the high level, the transistor Q2 is turned on / off in response to the signal derived from the NAND gate 12. As a result, the light emitting diode 15 blinks with the first light amount L1 necessary for transmitting normal transmission data. That is, the light emission and the light extinction at the first light amount L1 are performed corresponding to the data, whereby the optical data is sent from the optical fiber 21 to the bus 1.

On the other hand, when the control section 5 detects an abnormality, the error detection signal ERROR becomes high level. In such a period ΔT2, since the output signal of the NAND gate 12 is fixed to the high level, the transistor Q1 is NANDed.
Signal from gate 11 (inverted signal of jam signal JAM)
The conduction / interruption control is performed according to. Therefore, the light emitting diode 15 blinks with the second light amount L2.
That is, the light emission and the light extinction at the second light amount L2 are repeated, and the jam signal JAM is sent to the optical star coupler 20 through the optical fiber 21.

As described above, when abnormality is detected (period ΔT
The current flowing through the light emitting diode 15 in 2) is almost n times the current flowing during the period (periods ΔT1 and ΔT3) in which no abnormality is detected, so the second light amount L2 is the first light amount L1.
Will be larger than (for example, n times, and n
= 10, the light level is almost one digit higher. ). The current of about n times may exceed the maximum rating (40 to 50 mA) of the drive current of the light emitting diode 15.
That is, since the duty ratio of the jam signal JAM is 1: n, 1 / (n + 1) of one cycle of the jam signal JAM.
Even if a current which is almost n times as large as that in the normal state flows in the period of, the time average is only a current below the allowable limit in the light emitting diode 15. Therefore, it is not necessary to prepare a special light emitting diode for generating a large amount of light.

As described above, in this embodiment, the jam signal JAM sent from the node in which the abnormality has occurred in the jam area inserted between the frames is sent as a large amount of light optical data. As a result, a sufficiently high level electric signal can be generated in the photoelectric converter of each receiving unit 4 without being affected by the electrical holding level of the receiving unit 4 of each node Ni or the recovery time. As a result, when an abnormality occurs in any of the nodes, this is surely notified to all the nodes N1, N2, ....

Further, in this embodiment, one light emitting element is used instead of two light emitting elements for the generation of optical data with two kinds of light amounts of the first light amount L1 and the second light amount L2. Transmission of optical data with two types of light quantity is achieved by switching and passing two types of currents through the light emitting diode 15. Therefore, there is an advantage that one optical fiber 21 can be shared for transmitting optical data of two kinds of light amounts, and the configuration is not complicated and the cost is not significantly increased. Moreover, at the time of abnormality detection, the second light amount L2
Since the large current flowing through the light emitting diode 15 to generate the optical data of 1 only flows in a pulsed manner, it is not necessary to apply an excessively large maximum rated current as the light emitting diode 15.

In an actual optical communication system, in order to reliably transmit normal transmission data to all of a large number of nodes, it is necessary to use light emitting diodes of considerably high brightness. However, such a high brightness LED 10
At the time of filing of the present application, a light emitting diode of higher brightness capable of generating twice as much light and reliably notifying an abnormality of any node to all the remaining nodes has not been manufactured. Therefore, as a practical matter, there is no means for realizing abnormal data transmission with a large amount of light in the related art, and in this embodiment, one light emitting diode is commonly used for both normal data transmission and abnormal data transmission. At the same time, it can be said that one feature is that a large amount of light data is generated without destroying the light emitting diode by causing a large current to flow in a pulsed manner in the light emitting diode when abnormal data is transmitted.

FIG. 4 is a conceptual diagram showing the configuration of an optical communication system according to another embodiment of the present invention. 4, parts corresponding to the respective parts shown in FIG. 2 are designated by the same reference numerals. In this optical communication system, a plurality of nodes N1, N2, ... Are connected by a bus connection method to a bus 1 constituted by an optical fiber cable via an optical connector 2 and an optical fiber 21 to provide a local area.・ Forms a network. The configuration of each node Ni is similar to that of the first embodiment described above. In this embodiment, the bus 1, the optical connector 22 and the optical fiber 21 form an optical transmission line.

Even with such a bus connection type structure, the same operational effects as those of the first embodiment can be clearly achieved. The present invention is not limited to the above embodiment. For example, in the above example,
The jam signal JAM generated by the control unit 6 is a pulse signal having a predetermined duty ratio, and when an abnormality is detected, an inverted signal of the jam signal JAM is given to the drive circuit 14 so that a large current flows in a pulsed manner in the light emitting diode 15. Is being done. However, such a jam signal does not need to be created in the control unit 6, and a similar signal is created in the transmission unit 5, and the error detection signal ERRO from the control unit 6 is generated.
The light emitting diode 15 may be pulse-driven based on the signal generated in the transmission unit 5 in response to R.

Further, in the above embodiment, one light emitting diode 15 is commonly used for transmitting normal data and abnormal data, but two light emitting elements are used for transmitting each data. May be. In this case, if the light emitting element for transmitting the abnormal data is pulse-driven so that a large current flows only during a sufficiently short time, even if the maximum rated current of this light emitting element is not very large, A large amount of light data can be generated without destroying the light emitting element. When a light emitting element capable of continuously generating a large amount of light sufficient for all nodes to receive the abnormal data can be prepared, such a large amount of light emitting element may be used for transmitting the abnormal data. Needless to say. In this case, it is not necessary to pulse drive the light emitting element having the large amount of light.

Further, in the above embodiment, the case where the data communication is performed in the unit of the frame composed of the predetermined amount of data, and the jam area for detecting the abnormality of the node is provided between the frames is taken as an example. However, other data transmission formats may be applied. That is, if the normal data is transmitted with the first light amount and the abnormal data is transmitted with the second light amount larger than the first light amount, all the nodes can receive the abnormal data well, The present invention can be easily applied to any data transmission format.

Besides, various design changes can be made without departing from the spirit of the present invention.

[0041]

According to the optical communication system of the first aspect, abnormal data is sent out to the optical transmission line in a large amount of light.
When an abnormality occurs at any of the nodes, this can be surely notified to all the remaining nodes, regardless of variations in attenuation of optical data on the optical transmission line or the like.

According to the optical communication system of the second aspect, in addition to the above effects, one light emitting element whose maximum rated current is not so large is used, and normal transmission data at the first light intensity is obtained. And the transmission of abnormal data with a second light amount larger than the first light amount can be achieved, and there is an effect that the configuration is not complicated and the cost is not excessively increased. You can

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a configuration of a transmission unit used in each node of an optical communication system according to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram showing an overall configuration of the optical communication system.

FIG. 3 is a timing chart for explaining the operation.

FIG. 4 is a block diagram showing an overall configuration of an optical communication system according to another embodiment of the present invention.

[Explanation of symbols]

20 Optical Star Coupler 21 Optical Fiber 1 Bus Composed of Optical Fiber Cable 2 Optical Connector 4 Receiver 5 Transmitter 6 Controller (Abnormality Detection Means, Transmission Control Means) 11 NAND Gate 12 NAND Gate 13 Inverter 14 Drive Circuit (No. 1) 1 driving means, second driving means) 15 light emitting diode N1, N2 ... Node Q1 driving transistor Q2 driving transistor R1 resistor R2 resistor R3 resistor R4 resistor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04L 12/42 9299-5K H04L 11/00 331

Claims (2)

[Claims] 1. In an optical communication system in which a plurality of nodes are connected by a star connection method or a bus connection method via an optical transmission line, each node has a receiving unit for receiving optical data from the optical transmission line. And a transmitter capable of sending optical data to the optical transmission line with a first light amount or a second light amount larger than the first light amount, and for detecting that an abnormality has occurred in the node. The abnormality detection means and the transmission unit are controlled so that normal transmission data is transmitted at the first light amount, and when the abnormality detection means detects an abnormality in the node, the abnormality data is changed to the second light amount. An optical communication system, comprising: 2. The transmitting section includes one light emitting element, first driving means for flowing a first current corresponding to the first light amount to the light emitting element, and the second light emitting element to the light emitting element. A second drive means for supplying a second current corresponding to the amount of light, wherein the transmission control section drives the first drive means at the time of transmitting the normal transmission data so as to detect the abnormal data. The second driving means is driven at the time of transmission, and the optical communication system further includes means for driving the second driving means in a pulsed manner at a predetermined duty ratio. The optical communication system according to claim 1.