JP2778704B2 - Optical communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an optical communication system constituting a ring optical network, and more particularly to an improvement in an information transmission system.

(Prior Art) There are two types of optical communication systems constituting a ring optical network: a regenerative relay system based on regenerative relay at each terminal station and a non-regenerative relay system without regenerative relay at each terminal station. There is.

An example of the regenerative relay system is shown in FIG. In FIG. 10, A is a management station, and B, C and D are terminal stations. Each of the stations A to D includes an optical transmitter OS and an optical receiver OR, and is coupled to each other in a loop by optical fibers a to d. This method has an advantage that the transmission efficiency is high because each station can freely edit the signal on the loop such as erasing. But,
Uninterruptible countermeasures are required for each terminal station, and furthermore, a countermeasure for a failure in the event of even one station is also required.

FIG. 11 shows an example of the reproductionless relay system. In FIG. 11, A is a management station, B, C, and D are terminal stations. Each of the stations A to D includes an optical transmitter OS and an optical receiver OR. The management station A couples the optical transmitter OS and the optical receiver OR to both ends of the optical bus OB by optical fibers. This forms an optical loop. Each station B~D couples the optical combining unit OT _B2 ~OT _D2 for merging the optical splitter OT _B1 ~OT _D1 and the optical signal splitting the optical signal to the optical loop bus OB, respectively in accordance with the transmission direction OT _{B1 to} OT _D1
Attached to the input end, it is pulled out of the input end of the optical combiners OT _B2 ~OT _D2 is coupled to the output of the optical transmitter OS. According to this method, there is no problem as in the regenerative relay method, so that it can be applied to a network such as a subscriber optical network in which the loop manager cannot manage the power supply of each station, but the transmission efficiency is high. Is low.

That is, in the optical communication system of the regenerationless relay system, the optical signals on the optical loop bus cannot be erased at each terminal station, and while the optical signal transmitted from one terminal station is being transmitted, the other terminal station is not transmitting. When an optical signal is transmitted from a station, the signal overlaps in the optical loop bus, making it impossible to identify the signal at the time of reception. Therefore, a polling method is generally employed as an information access control method.

The polling method is a method in which a request signal is sequentially transmitted from a management station to each terminal station, and a response signal corresponding to the request signal is transmitted from each terminal station to the management station. In this polling method, a no-signal time, that is, a guard time is set in consideration of the maximum distance between the management station and the terminal station so that optical signals do not collide. This guard time must be increased in proportion to the light propagation distance, that is, the optical loop length. At this time, in order for the management station to receive an optical signal from each terminal station, each terminal station forms a preamble portion for clock recovery and reception level setting before a signal to be actually transmitted. The length of this preamble depends on the signal transmission speed,
The faster the information speed, the longer the preamble needs to be.

As described above, when the polling method is adopted, the guard time particularly increases as the number of terminal stations increases, so that the information transmission time given to one station is shortened accordingly. That is, since the transmission efficiency is determined by the size of the optical loop, the number of terminal stations, and the signal transmission speed, the transmission efficiency is extremely poor as compared with the regenerative relay system. Further, the conventional ring-shaped optical communication system has a fatal disadvantage that communication becomes impossible if a part of the loop is cut.

(Problems to be Solved by the Invention) As described above, in the conventional ring-shaped optical communication system, there is a problem that the regenerative repeater system requires measures against uninterruptible power failures and failures, resulting in poor maintenance efficiency. Since the regenerative relay system uses the polling system, there is a problem that the guard time becomes longer with an increase in the number of terminal stations, resulting in poor transmission efficiency. In addition, both methods have a fatal drawback that communication becomes impossible due to breakage of the loop.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a first object of the present invention is to increase transmission efficiency even in a non-playback relay, and a second object of the present invention. However, an object of the present invention is to ensure a communication state even when a loop is broken.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the first object, an optical communication system according to the present invention comprises a first optical transmitter for transmitting an optical signal of a first wavelength, A management station having a first optical receiver for receiving an optical signal having a second wavelength different from the first wavelength; an output end of a first optical transmitter of the management station; and a first optical receiver An optical loop bus formed by coupling a first optical fiber to an input end of the optical loop bus to form a first optical transmission line having a loop shape, and an optical branching / joining means coupled to an arbitrary portion of the optical loop bus; An optical receiver for receiving an optical signal of a first wavelength from the management station which is branched from the optical loop bus by the optical branching / joining means, and an optical signal of the second wavelength is transmitted, and the optical signal is transmitted to the optical Light to be sent to the optical receiver of the management station on the optical loop bus through the branching and joining means A plurality of terminal stations each having a transceiver, wherein the management station forms a communication period with the plurality of terminal stations as a frame, and within each frame period, transmits the transmission period of each of the plurality of terminal stations to the optical station. On the loop bus, allocation is performed so as to be continuous without any gaps in the order of being arranged in the transmission direction, transmission instruction information for instructing each terminal station on a transmission start position and a transmission period is generated in accordance with the allocation, and the transmission instruction information is framed. The first optical transmitter transmits the optical signal at the first wavelength to the optical loop bus by the first optical transmitter, and the plurality of terminal stations transmit a first signal from the management station transmitted through the optical loop bus. The optical receiver according to the wavelength of the received by the optical receiver to determine the transmission instruction information,
A transmission signal based on an optical signal of a second wavelength is transmitted from the optical transmitter during the transmission period designated from the transmission start position designated for itself in the transmission designation information, and placed on the optical loop bus, and the management is performed. The first feature is that the station extracts an optical signal having a second wavelength from among the optical signals obtained from the optical loop bus by the first optical receiver and extracts a signal from each terminal station. I do.

In order to achieve the second object, the management station of the optical communication system according to the first aspect further comprises: an optical branching and joining means for branching and joining an optical signal at both ends of the optical loop bus; A second optical transmitter for transmitting an optical signal having the same first wavelength as that of the first optical transmitter, the output end of which is coupled to a branch terminal of an optical loop bus opposite to the first optical transmitter;
And an optical transmitter for receiving an optical signal of the same second wavelength as the first optical receiver, the input end of which is the first optical receiver.
A second optical receiver coupled to the branch terminal of the optical loop bus on the opposite side of the optical receiver, and disconnection detecting means for detecting disconnection of the optical loop bus, the first optical transmitter and First
The optical receiver is used as a service system, the second optical transmitter and the second optical receiver are used as standby systems, and the optical signal is transmitted during the transmission period of the transmission instruction information and the entire transmission period allocated to each of the plurality of terminal stations. The frame period is set so as to be longer than a total value obtained by adding a time twice as long as the optical transmission time required from one end to the other end of the loop bus, and usually only the service system is operated, and the disconnection detecting means When a disconnection of the optical loop bus is detected, the standby system is driven together with the service system,
Optical branching and joining means provided in each of the plurality of terminal stations,
The optical signal from the optical transmitter is bidirectionally merged on the optical loop bus, and capturing both optical signals transmitted bidirectionally on the optical loop bus and guiding the optical signal to the optical receiver. 2.

Alternatively, the optical loop bus of the optical communication system according to the first aspect is a double optical transmission line further provided with a second optical fiber, and the management station further includes the same first optical transmitter as the first optical transmitter. A second optical transmitter for transmitting an optical signal of one wavelength, a second optical receiver for receiving an optical signal of the same second wavelength as the first optical receiver, and the first and second optical transmitters; A first optical transmitter coupled to both ends of the first optical fiber; and a first optical transmitter coupled to both ends of the first optical fiber.
The second optical transmitter and the second optical receiver at both ends of the second optical fiber so as to be opposite to the transmission direction of the first optical fiber. Is used as a standby system, and is twice as long as the optical transmission time required from one end to the other end of the optical loop bus during the transmission period of the transmission instruction information and the total transmission period allocated to each of the plurality of terminal stations. The frame period is set so as to be longer than the total value obtained by adding the above. Normally, only the service system is operated, and when only the disconnection of the first optical fiber is detected by the disconnection detecting means, the drive of the service system is performed. To the drive of the standby system, and when the disconnection of the first and second optical fibers is detected together, the service system and the standby system are simultaneously driven, and the optical branching / joining means provided in each of the plurality of terminal stations is provided. Then, the first And an optical branching / combining device coupled to each of the second optical fibers, an optical signal branched by each optical branching / combining device is guided to the optical receiver, and an optical signal from the optical transmitter is transmitted by each optical branching / combining device. A third feature is to join the first and second optical fibers according to their transmission directions.

According to a second or third aspect, the disconnection detecting means of the management station includes an optical receiver for receiving an optical signal of a first wavelength in parallel with an optical receiver for receiving an optical signal of a second wavelength of a detection system. A fourth characteristic is that the optical receiver is connected to the optical receiver and the optical receiver is determined to be normal while the optical signal of the first wavelength is being received, and is determined to be disconnected when reception becomes impossible.

(Operation) In the above-described optical communication system, in the configuration according to the first feature, an optical signal from the management station to the terminal station is transmitted at the first wavelength, and an optical signal from the terminal station to the management station is transmitted at the second wavelength. Therefore, both signals can be identified even if the optical loop bus is common. In addition, since the management station frames the optical signal to be transmitted and allocates the transmission periods of each terminal station in each frame so as to be continuous without any gap, and transmits the signals in the transmission period allocated to each terminal station, at least the guard No time is required, and transmission efficiency is significantly improved.

In the configuration according to the second aspect, the first optical transmitter and the second optical receiver are coupled to both ends of one optical loop bus, and conversely, the second optical transmitter and the second optical receiver are coupled. The receiver is combined to form a service system and a standby system, and the disconnection of the optical loop bus is always detected. Normally, only the service system is operated, and when the disconnection of the optical loop bus is detected, the service system is used. In addition, since control is performed to drive the standby system, even if a part of the optical loop bus is disconnected, an optical signal from the management station can be transmitted to all terminal stations. At this time, the transmission time is longer than the total value obtained by adding twice the optical transmission time required from one end to the other end of the optical loop bus to the transmission period of the transmission instruction information and the total transmission period allocated to each of the plurality of terminal stations. Since the frame period is set at each terminal station, the optical signal from the optical transmitter is merged in both directions of the optical loop bus at each terminal station.
The optical signal transmitted from each terminal station can be transmitted to the management station without collision between the terminal stations. For this reason, the communication state between the management station and each terminal station can be secured.

In the configuration according to the third aspect, a first optical transmitter and a first optical receiver are coupled to both ends of the first optical fiber with respect to the first and second optical fibers constituting an optical loop bus. And a second optical transmitter and a second optical receiver are coupled to both ends of the second optical fiber in a direction opposite to the transmission direction of the first optical fiber, and a standby system is provided. Normally, the disconnection of the first and second optical fibers is always detected and only the service system is operated, and when only the disconnection of the first optical fiber is detected by the disconnection detecting means, the drive of the service system is performed. To the drive of the standby system, and when the disconnection of the first and second optical fibers is detected, control is performed to simultaneously drive the service system and the standby system. Therefore, one of the first and second optical fibers or Even if both are disconnected, the optical signal from the management station is transmitted to all terminal stations. It is possible. At this time, the transmission time is longer than the total value obtained by adding twice the optical transmission time required from one end to the other end of the optical loop bus to the transmission period of the transmission instruction information and the total transmission period allocated to each of the plurality of terminal stations. Since the optical signal is transmitted from the terminal stations to the first and second optical fibers according to the transmission direction, the optical signals transmitted from the terminal stations collide between the terminal stations. It can be transmitted to the management station without performing. For this reason, the communication state between the management station and each terminal station can be secured.

In the configuration according to the fourth feature, the management station can receive both the optical signal of the first wavelength and the optical signal of the second wavelength in each system. It is possible to determine that the optical fiber has been disconnected, thereby enabling the selection control of the system.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows the configuration of an optical communication system which achieves the first object of the present invention, wherein A is a management station, B, C and D are terminal stations, and O is a terminal station.
B is an optical loop bus by the optical fiber, the management station A optical signal according to a second wavelength different from lambda ₂ and the optical transmitter OS _A and the first wavelength transmits the optical signal by the first wavelength lambda ₁ It has an optical receiver OR _A for receiving and an optical transmitter OS _A
Of the optical loop bus OB to one end of the optical loop bus
The input end of the OR _A is connected to the other end of the optical loop bus OB.

The terminal station B, C, D is (hereinafter referred to as optical tap) any optical branching device coupled to portions of the respective optical loop bus OB OT _B,
OT _C, and OT _D, optical tap OT _B, OT _C, the first optical receiver OR _B for receiving the optical signal of the wavelength lambda ₁ that is branched by the OT _D, OR _C, and OR _D, the second wavelength comprising optical tap OT _B sends the lambda ₂ of the optical signal, OT _C, OT _D optical transmitter placed on the optical loop bus OB via OS _B, OS _C, and OS _D.

Communication between the management station A and each of the terminal stations B, C, and D is performed by a polling method. At this time, the management station A frames the optical request signal of the first wavelength λ ₁ transmitted from the optical transmitter OS _A as shown in FIG.
The transmission periods of the terminal stations B, C, and D are allocated so as to be continuous without any gap in the order in which they are arranged in the transmission direction of the OB, and only the period allocated to each of the terminal stations B, C, and D with a predetermined time shift from the beginning of the frame. Transmission period instruction information for instructing transmission is assigned. The first wavelength lambda ₁ of the optical request signal generated in this way take the optical loop bus OB, some optical tap OT _B, OT _C, is branched at OT _D.

Each terminal station B, C, D are receive and transmit optical request signal by the first wavelength lambda ₁ from the management station A transmitted through the optical loop bus OB optical receiver OR _B, OR _C, with OR _D determine the time indication information, the optical transmitter OS _B, OS _C, a second optical response signal of the wavelength lambda ₂ transmits within the period instructed by the OS _D, optical tap OT _B, OT _C, OT _D
Put on the optical loop bus OB. At this time, the management station A
Since the wavelengths of the optical signal from the optical network and the optical signals from the terminal stations B, C, and D are different from each other, the signals are not disturbed even when the two signals merge. In addition, the response signals from the terminal stations B, C, and D are also loaded on the optical loop bus OB at timings shifted from each other, so that they are not affected by each other.

Response signals from the terminal stations B, C, and D are sent to the management station A on the optical loop bus OB. Administration second wavelength in the transmission signal from the optical loop bus OB by A in the optical receiver OR _A lambda ₂
And receives response signals from the terminal stations B, C, and D. At this time, the response signals from the terminal stations B, C, and D are optical signals of the same wavelength, and are transmitted for a predetermined period at a time determined from the beginning of the frame. It is.

Therefore, according to the optical communication system having the above configuration, the optical request signal from the management station A to the terminal stations B, C, and D is transmitted to the first wavelength λ ₁
Performed, the end station B, C, since the optical response signals from the D to the management station A at the second wavelength lambda _2, can be optical loop bus OB is a common identifying both signals, also , Management A
Then, the optical request signal to be transmitted is framed, and each frame is assigned to each of the terminal stations B, C, and D so as to be continuous for a predetermined period, and the optical response signal is transmitted during a predetermined period. This is unnecessary, so that the transmission efficiency can be remarkably improved.

FIG. 3 shows a configuration of an optical communication system for achieving the second object of the present invention, wherein A is a management station, B, C, and D are terminal stations, and O
B is an optical loop bus.

The management station A includes a first optical transmitter OS _A1 for transmitting an optical signal of the first wavelength λ ₁ and a second optical transmitter OS having the same configuration as the first optical transmitter OS _A1.
Comprising a _A2, first second optical receiver which the same structure with the optical receiver OR _A1 for receiving the second wavelength lambda ₂ of the optical signal OR _A2
Is provided. Then, the first optical transmitter OS _A1 and the second optical receiver OR _A2 are coupled to one end of the optical loop bus OB via the branching device BR _A1 , and the first optical receiver ORA _A1 and the second optical receiver OR _A2 are coupled. Optical transmitter OS _A2
The via splitter BR _A2 constituted by coupled to the other end of the optical loop bus OB.

Although not shown in detail, the management station A has a function of detecting disconnection of the optical loop bus OB, and normally uses the first optical transmitter OS _A1 and the first optical receiver OR _A1 ( When a loop disconnection is detected by the function described above, the second optical transmitter OS _A2 and the second optical receiver ORA _A2 are similarly used (standby system). That is, normally, only the normal system operates and the optical signal is transmitted only in the direction of arrow a. However, when the disconnection of the optical loop bus OB is detected, the standby system also operates and the optical signal also operates in the direction of arrow b. Transmitted.

The terminal B couples the bidirectional optical tap OT _B ′ to the optical loop bus OB, and connects the input / output terminal of the bidirectional optical tap OT _B ′ to the branching device B.
Optical receiver for receiving the first wavelength lambda ₁ of the optical signal through the R _B
Optical transmitter OS _B for delivering the OR _B and the second wavelength lambda ₂ of the optical signal
Are combined. Similarly, the terminal station C two-way optical taps OT _C ', splitter BR _C, the optical receiver OR _C, consists of an optical transmitter OS _C, the terminal station D is bidirectional optical tap OT _D' turnout BR _D optical receiver OR _D, comprised of the optical transmitter OS _D. That is, each terminal B,
C and D can receive an optical request signal from any direction on the optical loop bus OB, and send an optical response signal to the optical loop bus OB in both directions.

In the management station A, the optical request signal is generated in the same configuration as that shown in FIG. 2, and the frame length _{TF at} this time is different from the transmission direction of the optical request signal on the optical loop bus OB in normal use. At least twice the transmission time T _D in the optical loop bus OB is required as shown in the following equation so that the optical response signal from each terminal station going backward does not collide with the optical response signal of the next frame.

T _F −2T _D ≧ 0 Further, since the optical response time of each of the terminal stations B, C, and D is required, it is preferable that (T _F −2T _D ) / T _F ≧ 1/2 in consideration of the transmission efficiency. That is, by satisfying this condition,
At least half of the frame length can be secured as the data transmission period.

FIGS. 4 and 5 show the timing relationship between the optical request signal and the optical response signal in the optical communication system. In each figure,
The horizontal axis represents the distance from the management station A on the optical loop bus OB, and the vertical axis represents time. FIG. 4 shows a case where only the ordinary system is operating, and FIG. 5 shows a case where the optical loop bus OB is disconnected between the terminal stations C and D and the standby system is also operated.

In Figure 4, the light request signal transmitted from the management station A time T _D only takes to return to the management station A. Upon receiving the optical request signal, each of the terminal stations B, C, and D reads the transmission period instruction information at the head of the signal, and identifies the waiting time and the transmission period specified by the management station A. Here, the waiting time instructed from the management station A to each of the terminal stations B, C, D is t _B , t _C , t _D , respectively, and the transmission time of each of the terminal stations B, C, D is S _B , S _C , S _D. Here, the transmission times S _B , S _C , S _D of the respective terminal stations B, C, D can be set to any lengths as required. Also, the waiting time t _B ,
t _C and t _D are waiting times from when the transmission period instruction information is obtained to when the transmission of the immediately preceding terminal station is completed. As shown in FIG. 4, t _B = 0, t _C = S _B , t _D = S _B + S _C Therefore, the waiting times t _B , t _C , t _D of the terminal stations B, C, D are arbitrarily specified according to the transmission periods S _B , S _C , S _D. The optical response signals transmitted from the terminal stations B, C, and D are transmitted sequentially and continuously in the same direction as the optical request signal, but all are transmitted in the opposite direction. At this time, the optical response signals do not collide with each other as shown.

Here, as shown in FIG. 5, when the optical loop bus OB is disconnected between the terminal stations C and D, the first optical transmitter
The optical request signal transmitted from OS _A1 is transmitted to terminal station C, but does not reach terminal station D. Therefore, management station A
Is the standby system to detect loops break even is operated to deliver light request signal in the opposite direction from the second optical transmitter OS _A2. This optical request signal is transmitted to the terminal station D, but cannot proceed any further due to the loop disconnection. Therefore, the first optical transmitter OS _A1
Does not collide with the output of the second optical transmitter OS _A2 . The optical response signal transmitted from the terminal stations B and C is an optical loop bus O
Since it is merged bidirectionally on B, it is transmitted in the direction opposite to the arrow a and received by the second optical receiver OR _A2 of the management station A. Similarly, the optical response signal transmitted from the terminal station D is transmitted in the direction opposite to the arrow b, it is received by the first optical receiver OR _A1.

Therefore, the optical communication system having the above configuration enables a bidirectional transmission by forming a standby system using a part of a normal system,
Moreover, since the frame is set so that the collision of the optical signal does not occur on the optical loop bus OB, the communication state can be ensured even when the loop is broken.

FIG. 6 shows another embodiment of the optical communication system for achieving the second object of the present invention, wherein A is a management station, B, C, D are terminal stations, OB ₁ and OB ₂ are first, This is a second optical loop bus. The first and second optical loop buses can be realized by a two-core optical fiber.

The management station A includes a first optical transmitter OS _A1 for transmitting an optical signal of the first wavelength λ ₁ and a second optical transmitter OS having the same configuration as the first optical transmitter OS _A1.
Comprising a _A2, first second optical receiver which the same structure with the optical receiver OR _A1 for sending a second wavelength lambda ₂ of the optical signal OR _A2
Is provided. The first optical transmitter OS _A1 and the first light receiver OR _A1 first conventional system attached to both ends of the optical loop bus OB ₁ (transmission direction arrow a) to form a second the optical receiver oR _A2 and a second optical transmitter OS _A2 as the transmission direction is reversed, conventional system a second auxiliary system linked to both ends of the optical loop bus OB ₂ (transmission direction arrow b Direction).

The terminal station B is coupled to the first and second optical loop buses OB ₁ and OB ₂ , respectively, and the first and second optical taps OT _B1 and OTB ₂ having a single branching and joining direction are provided. First and second optical receivers OR _B1 and OR _B2 for receiving an optical signal of wavelength λ ₁ , second wavelength λ
First it sends the _second optical signal, a second optical transmitter OS _B1, OS _B2
Is provided. Then, a first optical receiver OR _B1 is coupled to the branch output side of the first optical tap OT _{B1, and} a first optical transmitter OS _B1 is coupled to the merging input side to form a service system. Light tap OT
_A second optical receiver OR _B2 is coupled to the branch output side of _B2 , and a second optical transmitter OS _B2 is coupled to the merging input side to form a standby system. Similarly, terminal station C has first and second optical taps OT
_C1 , OT _C2 , first and second optical receivers OR _C1 , OR _C2 , first and second optical receivers
The terminal D is composed of first and second optical taps OT _D1 and OT _D2 , and first and second optical receivers O _C1 and O _C2.
R _D1 , OR _D2 , and first and second optical transmitters OS _D1 and OS _D2 .

In the above arrangement, since the regular and standby systems are completely independent, if the optical loop bus OB ₁ conventional system is broken it is possible to ensure the communication state by switching to the spare system. However, in this configuration, two sets of optical transmitters and optical receivers must be provided in the terminal station, and the burden on the terminal station is large. Therefore, if the configuration of each terminal station is as shown in FIG. 7 (representing terminal station B), the burden on the terminal station can be reduced.

In Figure 7, the optical receiver OR _B is coupled to the first, each branch output of the second optical tap OT _B1, OT _B2 via the first splitter BR _B1, the optical transmitter OS _B Part the first through the second splitter BR _B2, are coupled to each merging input of the second optical tap OT _B1, OT _B2. That is, the optical receiver OR _B can receive branches input light signal transmitted through any of the optical loop bus OB _1, OB ₂ above, the optical transmitter OS _B is either an optical signal optical loop bus OB ₁ and OB ₂ can be merged in a predetermined transmission direction.

That is, even in this configuration, since bidirectional communication is possible by the first and second optical loop buses OB ₁ and OB ₂ , the third
By forming a frame in the same manner as in the system shown in the figure, a communication state can be ensured even when both optical loop buses OB ₁ and OB ₂ are disconnected. That is, normally, only the normal system is operated, and the standby system is switched by detecting disconnection of the normal system. Further, when the standby system disconnection is detected, both systems are operated. At this time, the first light request signal sent from the optical transmitter OS _A1 of the management station A is transmitted to the terminal station that is coupled to a broken point through the first optical loop bus OB _1. The terminal receiving this optical request signal transmits the optical response signal to the first and second optical response signals.
To the optical loop buses OB ₁ and OB ₂ , so that the management station A can receive the signal at the second optical receiver ORA ₂ . Similarly,
Second optical request signal sent from the optical transmitter OS _A2 of the management station A is transmitted to the terminal station that is coupled to a broken point through the second optical loop bus OB _2. The terminal receiving this optical request signal transmits the optical response signal to the first and second optical loop buses OB ₁ and OB.
₂ , the management station A can receive the first optical receiver OR _A1 .

Therefore, the optical communication system having the above-described configuration can perform bidirectional transmission by the first and second optical loop buses OB ₁ and OB _{2 and} prevent collision of optical signals on the optical loop buses OB ₁ and OB _2. The communication state can be ensured not only when the normal system is disconnected but also when the standby system is disconnected.

In the configuration of FIGS. 3 and 6 (or FIG. 7), the detection of the loop disconnection can be realized by the configuration of FIG. 8 and FIG.

FIG. 8 shows a configuration in a case where the optical communication system shown in FIG. 3 has an optical loop bus disconnection detection function. The Figure 3 the same parts in FIG. 8 are denoted by the same reference numerals, and description thereof is omitted, the system an optical splitter BR ₂ of the management station A and a third branch, OR _A1, OS other _A2, the third optical receiver for receiving the first wavelength lambda ₁ of the optical signal
Composed of OR _A3 . According to this configuration, since the optical signal from the first optical transmitter OS _A1 is continuously transmitted by the third optical receiver OR _A3 , the optical signal can be simply detected. When the detection becomes impossible, it can be determined that the loop is broken.

FIG. 9 shows a configuration in the case where the optical communication system shown in FIG. 6 has an optical loop bus disconnection detection function. In FIG. 9, the same parts as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted. This system, each splitter BR _1, BR ₂ to the input terminals of said first and second optical receiver OR _A1, OR _A2 provided, two optical signals from the optical loop bus OB _1, OB ₂ And third and fourth optical receivers OR _A3 and ORA _A4 for receiving an optical signal of the first wavelength λ ₁ at each branch end. According to this configuration, the optical request signals from the optical transmitters OS _A1 and OS _A2 can be detected for each frame by the third and fourth optical receivers OR _A3 and ORA _A4 , so that the third optical receiver OR _A3 first optical loop bus OB ₁ when it is no longer able to detect the light request signal can be determined to have been disconnected, the first time is no longer able to detect the light request signal by the fourth optical receiver OR _A4 It can be determined that the _second optical loop bus OB2 is disconnected.

With the above configuration, even if a loop disconnection is detected, it is possible to perform control so as to automatically detect the loop disconnection and secure the communication state.

[Effects of the Invention] As described above, according to the present invention, transmission efficiency can be increased even in the case of non-playback relay, and a communication state can be ensured even if a loop is broken.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical communication system for achieving the first object according to the present invention, and FIG. 2 is a diagram for explaining an optical request signal framing means of the embodiment. FIG. 3 is a block diagram showing an embodiment of an optical communication system for achieving the second object according to the present invention, and FIGS. 4 and 5 show optical requirements when the loop is not broken and when the loop is broken, respectively. FIGS. 6 and 7 are diagrams for explaining a timing relationship between a signal and an optical response signal. FIGS. 6 and 7 are block diagrams showing another embodiment of the optical communication system for achieving the second object according to the present invention. FIG. 9 and FIG. 9 are block diagrams showing a means for detecting loop disconnection in the system of FIG. 3, FIG. 6 or FIG. 7, and FIG. 10 and FIG. 11 are block diagrams showing the configuration of a conventional optical communication system. It is. A: Management station, B, C, D: Terminal station, OB: Optical loop bus, O
S: Optical transmitter, OR: Optical receiver, OT: Unidirectional optical branching / combining device, OT ': Bidirectional optical branching / combining device, BR: Branching device.

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI H04L 12/42 (72) Inventor Taro Shibaki 1 Toshiba-cho, Komukai, Koyuki-ku, Kawasaki-shi, Kanagawa Inside the Komukai plant of Toshiba Corporation (56) References JP-A-57-142053 (JP, A) JP-A-56-69943 (JP, A) JP-A-58-34647 (JP, A) JP-A-62-86941 (JP, A) JP-A-62-222725 (JP, A) JP 60-13537 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04B 10/00-10/28 H04J 14/00-14/08

Claims (4)

(57) [Claims] 1. A management station having a first optical transmitter for transmitting an optical signal of a first wavelength and a first optical receiver for receiving an optical signal of a second wavelength different from the first wavelength. And an output end of the first optical transmitter of the management station and an input end of the first optical receiver are connected by a first optical fiber to form a loop-shaped first optical transmission line. An optical loop bus, an optical branching / joining unit coupled to an arbitrary portion of the optical loop bus, and receiving an optical signal of a first wavelength from the management station branched from the optical loop bus by the optical branching / joining unit. And a plurality of optical transmitters each of which transmits an optical signal of the second wavelength and transmits the optical signal to the optical receiver of the management station by passing the optical signal on the optical loop bus through the optical branching / joining means. And the management station frames communication periods with the plurality of terminal stations. Within each frame period, the transmission periods of the plurality of terminal stations are allocated so as to be continuous on the optical loop bus in the order in which they are arranged in the transmission direction without any gaps. Transmission instruction information for instructing a transmission period is generated.
The optical transmitter transmits the optical signal to the optical loop bus, and the plurality of terminal stations receive the optical signal having the first wavelength from the management station transmitted through the optical loop bus by the optical receiver. The transmission instruction information is determined, and a transmission signal of an optical signal of a second wavelength is transmitted from the optical transmitter during a transmission period instructed from a transmission start position instructed to the self in the transmission instruction information, and So that the management station extracts an optical signal of a second wavelength from among the optical signals obtained from the optical loop bus by the first optical receiver and extracts a signal from each terminal station. An optical communication system, comprising: 2. The management station further includes an optical branching / joining means for branching / joining an optical signal at both ends of the optical loop bus, and an optical signal having the same first wavelength as the first optical transmitter. A second optical transmitter whose output end is coupled to a branch terminal of an optical loop bus opposite to the first optical transmitter, the second optical transmitter being the same as the first optical receiver. A second optical receiver for receiving an optical signal of two wavelengths, the input end of which is coupled to a branch terminal of an optical loop bus opposite to the first optical receiver; Disconnection detecting means for detecting disconnection of the loop bus, using the first optical transmitter and the first optical receiver as a normal system, and using the second optical transmitter and the second optical receiver as a standby system, One of the optical loop buses is used during a transmission period of the transmission instruction information and a total transmission period allocated to each of the plurality of terminal stations. From setting the frame period to be longer than the total value obtained by adding twice the time of light transmission time required to the other end, usually activates only the conventional system,
When the disconnection of the optical loop bus is detected by the disconnection detecting means, the standby system is driven together with the service system, and the optical branching / joining means provided in each of the plurality of terminal stations,
An optical signal from the optical transmitter is bidirectionally merged on the optical loop bus, and both optical signals transmitted bidirectionally on the optical loop bus are taken and guided to the optical receiver. The optical communication system according to claim 1, wherein 3. The optical loop bus is a double optical transmission line further provided with a second optical fiber, and the management station further comprises a first optical transmitter same as the first optical transmitter.
A second optical transmitter for transmitting an optical signal having a wavelength of
A second optical receiver for receiving an optical signal having the same second wavelength as the optical receiver, and a disconnection detecting means for detecting disconnection of the first and second optical fibers; A first optical transmitter and a first optical receiver coupled to both ends of a fiber are used as a normal system, and the transmission direction of the first optical fiber is opposite to the transmission direction of the first optical fiber at both ends of the second optical fiber. The second optical transmitter and the second optical receiver are combined and used as a standby system, and the optical loop bus is used during a transmission period of the transmission instruction information and a total transmission period allocated to each of the plurality of terminal stations. The frame period is set so as to be longer than a total value obtained by adding a time twice as long as the optical transmission time required from one end to the other end, and normally only the normal system is operated, and the first line is detected by the disconnection detecting means. When only the disconnection of the optical fiber is detected, Switching from the driving to the driving of the standby system, and when the disconnection of the first and second optical fibers is detected together, the normal system and the standby system are simultaneously driven; In the means, an optical branching / combining device is coupled to each of the first and second optical fibers, an optical signal branched by each optical branching / combining device is guided to the optical receiver, and an optical signal from the optical transmitter is transmitted. The optical communication system according to claim 1, wherein each of the optical branching / joining devices joins the first and second optical fibers according to their transmission directions. 4. The disconnection detecting means of the management station includes a first line in parallel with an optical receiver for receiving an optical signal of a second wavelength of a detection system.
An optical receiver for receiving an optical signal having a wavelength of is coupled to the optical receiver, and a normal state is determined while an optical signal having a first wavelength is being received by the optical receiver, and a disconnection is determined when reception is disabled. The optical communication system according to claim 2 or 3, wherein