JP2002204223A - Optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmission system which can correctly reproduce a conference signal and a monitor signal with only two repeaters opposite each other. SOLUTION: One or more reproducing repeaters 30 to 50 or linear repeaters 60 and 70 are connected between multiplexing terminal devices to constitute a transmission system. The repeaters 30 to 50 have local oscillators 36 to 38, 46 to 48 and 56 to 58 respectively or the linear repeaters 60 and 70 have local oscillators 62 and 72 respectively. Phase monitor parts 37, 47, 63, and 73 discriminate between a reference clock which is sent out of the multiplexing terminal device 10 or 20 and synchronized with a network and a reference clock which sent out of one of the reproducing repeaters 30 to 50 or the linear repeater 60 or 70.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission system, and more particularly, to an optical transmission system comprising a multiplexing terminal device, an optical regenerative repeater, an optical linear repeater and an optical fiber transmission line connecting these devices in a synchronous network communication system. Related to transmission systems.

[0002]

2. Description of the Related Art In a repeater of a synchronous digital communication or transmission system, a clock signal is used as an operation reference. Conventional techniques in such technical fields include, for example, "Optical repeater monitoring system" in JP-A-8-237196, "Clock switching system in intermediate relay station" in JP-A-5-235815, and JP-A-5-19925.
No. 0, “Clock switching method” and the like.

FIG. 9 is a block diagram showing a configuration of a conventional general optical transmission system. This optical transmission system
It is composed of a plurality of optical regenerative repeaters (also referred to simply as repeaters) 103, 104 and 105 connected by optical fibers between opposing multiplexing terminal equipments (line terminal multiplexers: LT-MUXs) 101 and 102. . A plurality of low-speed optical signals 108, 109, 110, 111
Is a high-speed optical signal 1 at the multiplexing terminal devices 101 and 102.
06 and 107. High-speed optical signals 106 and 107 output from multiplexing terminal devices 101 and 102
Receive signal power attenuation due to optical fiber loss.
Therefore, the repeaters 103, 104, and 105 are arranged at predetermined intervals to receive and reproduce the attenuated high-speed optical signal. And
The transmission distance between the multiplexing terminal devices 101 and 102 is increased by reducing the deterioration of the signal waveform in the optical fiber.
The high-speed optical signals 106 and 107 after transmission are again converted into a plurality of low-speed optical signals 108 and 1 by the multiplexing terminal devices 101 and 102.
09, 110, and 111.

[0004] The multiplexing terminal devices 101 and 102 have a communication function with the maintenance and operation device, and a maintenance and operation communication channel (for example, S) in the transmission frame with each of the repeaters 103 to 105.
R included in the STM frame in the DH transmission frame
Using the D1, D2, and D3 bytes in the SOH or the channel in the LSV (monitoring control signal processing unit), the communication function for transmitting and receiving the maintenance operation information and the relays 103 to 105 are monitored based on the maintenance operation information. Has functions. Each of the repeaters 103 to 105 has a function of monitoring a relay section including a connected optical fiber, and uses a maintenance operation channel in a transmission frame or a channel in an LSV (monitoring control signal processing unit) to transmit maintenance operation information. It has a communication function for transmitting and receiving. Using these functions, the multiplexing terminal equipment 101
And a regenerative repeater and a linear repeater connected between the multiplexing terminal apparatuses 101 and 102 are remotely monitored via the multiplexing terminal apparatuses 101 and 102.

[0005] The regenerative repeaters 103 to 105 are a single repeater system and include a WE (West-to-East) repeater unit and an EW repeater. Transmission signals from the multiplexing terminal devices 101 and 102 are received and demodulated, re-timed (timing-adjusted) by a reproduced clock signal reproduced by a clock extraction circuit, and converted to a transmission signal synchronized with a reference clock signal of a synchronous network. Send out. In the regenerative repeaters 103 to 105, the monitoring signal separation circuit separates the main signal and the monitoring signal in the transmission frame. The separated monitoring signal is processed in the monitoring circuit unit. It is determined whether the maintenance and operation information transferred via the communication channel provided with the other device is addressed to the own device or the other device. If the information is addressed to the own device, a monitoring control process according to the information content is performed. On the other hand, if it is addressed to another device,
It has an algorithm for transferring the maintenance and operation information to an adjacent other device.

FIG. 10 is a block diagram showing a configuration of a conventional optical transmission system when a linear repeater is inserted. The linear repeaters 203 and 204 arranged and connected between the opposing multiplexing terminal devices 201 and 202 are linear repeaters that amplify the optical signal as it is without reproducing the optical signal. The transmission signal from the reproduction relay 205 is amplified as an optical signal.

FIG. 11 shows a specific configuration example of the linear repeater (eg, 203) shown in FIG. One relay system includes a WE direction relay unit 301 and an EW direction relay unit 302. The main signal 30
Apart from 3, 304, 305, 306, wavelength multiplexed maintenance operation information signals (LSV signals) 307, 308, 30
9 and 310 perform monitoring control processing according to the information content, wavelength-multiplex the LSV signal with the main signal, and transmit it.

FIG. 12 shows a principle diagram of a clock system in the repeater. FIG. 12 includes multiplexing terminal devices 401 and 402, linear repeaters 403, 404, and 405, and reference clock generators 406 and 407. Each linear repeater 403, 404, 405 is a pair of clock oscillation circuits 408-409, 410-411, 412-, respectively.
413 and a pair of selectors 414-415, 416-
417, 418-419. The reference clock generators 406 and 407 supply clocks synchronized with the network by the clock supply device to the multiplexing terminal devices 401 and 402. Then, the linear repeaters 403 to 405 transmit signals in synchronization with the reference clock. As an operation example, when the upstream transmission signal of the linear repeater 403 is interrupted, this relay unit sends out a signal based on the clock signal from the clock oscillation circuit. The selector 414 is switched by the reception input disconnection alarm signal, and the clock oscillation circuit 40
9 to perform communication with the opposing device based on the clock signal. Since there is no synchronous relationship between the clock signal of the clock oscillation circuit 409 and the reference clock signal 407 of the synchronous network, a slip or the like occurs when the opposite multiplexing terminal device 402 receives this data. In the clock switching method in the intermediate relay station of the synchronous network communication system, when a transmission signal from the upstream in the relay unit is interrupted, the monitoring information to the downstream is switched by switching to a reproduction clock signal reproduced in another relay unit. Secure communication. Accordingly, it has been proposed that a signal synchronized with the reference clock signal is transmitted and multiplexed even in the case of a transmission line failure to the repeater. Also, a linear repeater that amplifies an optical signal without reproducing the optical signal has been developed. Therefore, as shown in FIG. 10, a linear repeater can be used as a repeater together with a conventional regenerative repeater. This linear repeater is less expensive than a regenerative repeater due to its simple configuration, and its use can reduce the cost of the optical transmission system.

FIG. 13 shows a principle diagram of a clock system of the above-described linear repeater. In this clock system, the optical amplifier 5 amplifies transmission signals 513 and 514 from the multiplexing terminal equipment.
01, 502, demultiplexer (DMUX) 503, 50
8, clock extraction circuits 504 and 509, selector 50
5, 510, multiplexers (MUX) 506, 511, and clock oscillation circuits 507, 512.

FIG. 14 shows a detailed configuration diagram of a clock system when a linear repeater is opposed. Transmission signals 601 and 602 from the multiplexing terminal equipment are transmitted to optical amplifiers 603, 604 and 60, respectively.
5 and 606, the optical signal is amplified as it is. Separately from the main signal, a wavelength multiplexed maintenance operation information signal (LSV signal)
The reproduced clock signals 611, 612, 613, and 614 extracted and reproduced from 607, 608, 609, and 610 are used as L
The SV signals are LSV signals 615, 616, 61 synchronized with the reference clock signal of the synchronous network by being retimed.
7, 618 are wavelength multiplexed with the main signal and transmitted. FIG. 15 is a block diagram showing a basic configuration of a conventional repeater monitoring system. Multiplexing terminal devices 651 and 655 arranged and connected at both ends of the optical regenerators 652 and 654 and the optical linear repeater 653 are bidirectionally connected to the maintenance and operation device 650 to monitor and control.

[0011]

In the prior art as described above, when an upstream transmission signal is interrupted by a regenerative repeater, a slip or the like occurs when the downstream multiplexing terminal equipment receives this data. To prevent this from happening, do not use a clock from a self-clocked oscillator. Instead, by turning back the clock received from the downstream multiplexing terminal device, a means for multiplexing the meeting signal and the supervisory control signal on the overhead of the main signal with the clock synchronized with the multiplexing terminal device and sending it downstream is provided. is suggesting. If this method is adopted for a linear repeater that amplifies an optical signal without regenerating an optical signal, the configuration of the clock system differs from that of the optical regenerative repeater. Can be applied to the linear repeater by replacing with the clock of the supervisory control system (LSV) signal in the linear repeater, but it has the following problems.

First, the clock switching method of the regenerative repeater and the linear repeater describes a case where one side is disconnected from the multiplexing terminal equipment due to a transmission line failure or the like. It is not possible to correctly reproduce a meeting signal or a monitoring signal when only a repeater is connected to each other. The regenerative repeater and the linear repeater have a characteristic of transmitting in synchronization with the reference clock from the multiplexing terminal device. Therefore, when the multiplexing terminal device is not connected upstream or downstream, such as at the time of construction, the reference clock is not used. For example, even when switching to a self-oscillator, opposing regenerative repeaters and linear repeaters operate with different clocks respectively, and the receiving device slips in data, and corrects the meeting signal and the monitoring signal. This is because they cannot be played.

Second, in order to solve the first problem described above, a regenerative repeater provided with a selector unit for switching between three clocks of a clock received from upstream, a return clock received from downstream, and a self-oscillator. And linear repeaters. In this case, if the selectors of the devices facing each other when only the repeaters are connected to each other select the return clock received from downstream in each repeater, the clock is lost.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide an optical transmission system capable of correctly reproducing a meeting signal and a monitoring signal by opposing only a repeater to a repeater.

[0015]

An optical transmission system according to the present invention is a system in which one or more repeaters are connected between multiplexing terminal devices each having a multiplexing unit and a reference clock generator. The repeater includes a clock switching selector and a clock generator that generates an internal clock. The selector selects an internal clock from the clock generator or a reference clock from a reference clock generator of the multiplexing terminal device.

According to a preferred embodiment of the optical transmission system of the present invention, the repeater is a regenerative repeater or a linear repeater. When the multiplexing terminal device is not connected and the reference clock is not present and only the repeater-to-repeater is connected, priority is given to the opposing repeater, and the clock generator of one of the opposing repeaters is used as the reference clock. Operate. The repeater includes a clock extracting unit that extracts a clock from a device facing the relay unit, and a phase monitoring unit that monitors a phase of a clock that is selectively output by the selector. The selector is switched according to a predetermined switching condition. Each repeater is WE
An ST-side and an EAST-side clock generator are provided, and depending on whether the selector is the WEST-side or the EAST-side, the operation time of the selector is changed to determine which clock generator operates as a reference between the opposing devices.

[0017]

Next, the configuration and operation of a preferred embodiment of an optical transmission system according to the present invention will be described in detail with reference to the accompanying drawings.

First, FIG. 1 is a basic configuration diagram centering on a clock switching unit of a preferred embodiment of an optical transmission system according to the present invention. This optical transmission system includes a pair of multiplexing terminal devices 10 and 20 arranged opposite to each other and a plurality (three in the specific example shown) of repeaters arranged and connected between these multiplexing terminal devices 10 and 20. (REP) 30, 40, 50. Multiplexing unit 1 of multiplexing terminal devices 10 and 20
2, 14, 22 and 24 are supplied with reference clocks from reference clock generators 15 and 25, respectively.
In the multiplexing terminal devices 10 and 20, the multiplexing units 12, 2
2 is an uplink multiplexing unit, and multiplexing units 14 and 24 are downlink multiplexing units. Each of the repeaters 30, 40, 50 includes a pair of selectors 32-34, 42-44, 52-54 and a pair of clock oscillation circuits 36-38, 46-48,
56-58.

FIG. 2 is a block diagram showing a more detailed configuration of the repeaters in FIG. 1, for example, the repeaters 30 and 40. The repeater 30 includes the selectors 32 and 34 described above with reference to FIG.
And clock oscillation circuits 36 and 38, demultiplexers (DMUX) 31a and 31b, and a clock extraction unit 33
a, 33b, multiplexers (MUX) 35a, 35b
And phase monitoring units 37a and 37b. Similarly, the repeater 40 includes selectors 42 and 44 and clock oscillators 46 and 4 in addition to the main signal transmission line having an optical amplifier.
8, demultiplexers 41a and 41b, clock extraction circuits 43a and 43b, multiplexers 45a and 45, and phase monitoring units 47a and 47b.

Next, referring to FIG. 3, FIG. 4 and FIG.
The operation of the optical transmission system of the present invention shown in FIGS. 1 and 2 will be described. First, FIG. 3 shows the flow of the reference clock in the optical transmission system when everything is operating normally.
In this case, as shown by the dotted line in FIG. 3, the reference clock from the reference clock generator 15 is
Of the multiplexing terminal device 20 via the multiplexing unit 12 and the repeaters 30, 40, and 50. The reference clock from the reference clock generator 25 is supplied to the multiplexing unit 14 of the multiplexing terminal device 10 via the multiplexing unit 24 of the multiplexing terminal device 20 and the repeaters 50, 40, and 30. . As described later in detail, selectors 32-34 and 42-
44, 52-54 select a clock extracted from the own device as a reference clock. At this time, each repeater 30,
Reference numerals 40 and 50 operate in synchronization with the reference clock of the connected multiplexing terminal equipment.

Next, FIG. 4 shows an operation state of the clock switching system when a transmission line failure occurs between the multiplexing terminal device 10 and the repeater 30, as indicated by the X mark. In this case, the reference clock from the reference clock generator 25 connected to the multiplexing terminal equipment 20 is looped back via the repeaters 50, 40 and 30 and further in the repeater 30, and
The process returns to the multiplexing terminal device 20 via 0 and 50. At this time, since the opposing device is operating in synchronization with the reference clock of the multiplexed terminal equipment to be connected, the opposite device operates by turning the clock back to synchronize with the reference clock of the network. FIG. 5 shows a reference clock route at the time of constructing the optical transmission system. The state between the repeater 30 and the multiplexing terminal apparatus 10 and the state between the repeater 50 and the multiplexing terminal apparatus 20 are cut off as indicated by X. In this case, as shown by the dotted line in FIG.
The reference clock 58 of the repeater 50 is looped back to the repeater 50 via the repeaters 40 and 30.

FIG. 6 is a block diagram showing optical linear repeaters (L-REPs) 60 and 70 in the optical transmission system according to the present invention. FIG. 7 is an operation explanatory diagram of the optical linear repeater of FIG. FIG. 8 is an explanatory diagram of the switching condition of the selector in FIGS. 6 and 7. In FIG. 6, a pair of linear repeaters (L-REP) 60 and 70 are connected to face each other. For example, the linear repeater 60 has the EAST side facing the linear repeater 70 and multiplexes and transmits an optical amplifier unit that amplifies the main signal transmission signal as an optical signal and a signal transmitted from the monitoring control interface unit 67. A MUX 64, a DMUX 65 that receives a monitoring control signal from the opposing device 70 and sends it to the monitoring control interface 77, and a C that receives the monitoring control signal from the opposing device 70 and extracts a clock signal
An LK extraction unit 66, a selector (SEL) 61 that determines a clock switching condition, and selects an appropriate reference clock;
A self-oscillator (OSC) 62, a clock signal extracted from a west-side monitoring control signal in the own device 60,
And a phase monitoring unit 63 that compares the clock signals extracted from the monitoring control signal from the CPU and generates a part of the switching condition. On the other hand, the linear repeater 70 has the same constituent elements 71 to 77 as the linear repeater 60 described above, with the WEST side facing the linear repeater 60.

Next, the operation of the embodiment of the clock switching system according to the present invention will be described in detail. Under the conditions shown in the normal reference clock route diagram in FIG. 3, the selector 61 of the linear repeater (L-REP) 60 in FIG. 6 selects the clock C16 extracted from the EAST side as the reference clock. In addition, the selector 71 of the linear repeater 70
The clock C22 extracted from the T side is selected as a reference clock. At this time, the linear repeaters 60 and 70 in FIG. 6 operate in synchronization with the reference clocks of the multiplexing terminal devices connected to the west side and the east side, respectively.

Under the conditions shown in the reference clock route diagram at the time of transmission line failure in FIG. 4, the selector 61 of the linear repeater 60 in FIG. 6 uses the clock C16 extracted from the EAST side of the linear repeater 60 as a reference clock. select. The selector 71 of the linear repeater 70 selects the clock C22 extracted from the west side of the linear repeater 70 as a reference clock. At this time, the linear repeaters 60 and 70 in FIG. 6 operate in synchronization with the reference clock signal of the multiplexing terminal equipment connected to the EAST side.

Under the conditions shown in the reference clock route diagram at the time of constructing the optical transmission system in FIG. 5, the selectors 61 and 71 of the linear repeaters 60 and 70 in FIG. Is selected as a reference clock. At this time, the linear repeater 6 in FIG.
0 and 70 operate in synchronization with the clock C23 from their own oscillators 62 and 72, respectively.

The switching condition of the selector 61 at the time of the basic operation will be described with reference to FIG. Linear repeater 60
, The clock of the opposing device, the clock of the own device, and the clock of the OSC 62 are input to the selector 61.
The selector 61 is configured to select and output an optimum clock from among these clocks. The linear repeater 60 performs internal processing based on the selected clock and sends out a monitoring control signal. The clock of its own device and the reference clock selected by the selector 61 are transmitted to the phase monitor 6.
3 and a clock input to the selector 61;
The slip of the reference clock after the selection is monitored. The phase monitoring unit 63 for switching the selector 61 is connected to the WEST side or the E side.
There is a time control circuit that switches to the OSC clock and makes a transition according to a determination signal on the AST side.

Next, under the conditions shown in the normal reference clock route diagram in FIG. 3, the selector 61 in FIG.
The clock extracted from the own device is selected as a reference clock. At this time, the linear repeater 60 operates in synchronization with the reference clock of the multiplexed terminal equipment to be connected. Also,
Under the conditions shown in the reference clock route diagram at the time of transmission line failure in FIG. 4, the selector 61 in FIG.
A clock of 0 is selected as a reference clock. At this time, since the opposing device 70 is operating in synchronization with the reference clock of the multiplexed terminal equipment to be connected, it operates in synchronization with the reference clock of the network by turning the clock back. FIG. 8 shows the switching conditions of the selector 61. The operation at this time corresponds to a in the state transition diagram of FIG. 8B, and when a transmission line failure occurs, the clock extracted from the own device is switched to the clock of the opposite device 70.

Under the conditions shown in the reference clock route diagram at the time of constructing the optical transmission system in FIG. 5, the selector 61 in FIG. 7 adopts a different clock selection method depending on whether it is the WEST side or the EAST side. The detailed operation will be described below. When the linear repeater 60 is initially started up and the optical cable is not connected, the clock extracted from the own device and the clock of the opposite device 70 input to the selector 61 do not exist. At this time, selector 61
The OSC clock is selected according to the sequence indicated by b or f in (B). That is, the linear repeaters 60 and 70 in FIG. 6 are in a state where the OSC clock is selected by the selectors 61 and 71, respectively.

Next, the linear repeaters 70 to 6 in FIG.
When the optical signal is connected to 0, the phase monitoring unit 63 of the linear repeater 60 transmits the clock from the OSC 62 of its own device,
The clock from the OSC 72 of the opposing device 70 is compared, and an error is detected. At that time, the selector 61
Selects the clock of the opposing device 70 according to the sequence shown in c of FIG. 8B.

Next, the linear repeaters 60 to 70 shown in FIG.
When the optical signal is connected to the optical repeater 70, the phase monitoring unit 73 of the linear repeater 70 compares the clock from the OSC 72 of the own device with the OSC clock of the own device which is turned back by the opposite device 70. Not detected. then,
The selector 61 enters a state in which the OSC clock is selected according to the sequence shown in g of FIG.

Next, the linear repeaters 60 and 70 in FIG.
If any of the devices (repeater 60 or 7
With reference to 0), one is synchronized with the self-oscillator clock, and the other is synchronized with the oscillator clock of the opposing device, so that the devices can be synchronized. As a special operation, when the selectors 61 and 71 of both devices (repeaters 60 and 70) simultaneously select the clock of the opposing apparatus, the WEST side and the EAST determine which of the linear repeaters 60 and 70 operates as a reference. By giving a time lag to the switching on the WEST side, the WEST side is prioritized.

Next, the linear repeaters 60 and 70 in FIG.
The operation when a multiplex relay device is connected to one device and a reference clock is input from a clock supply device from a state where one device is synchronized with the other device as a reference will be described. . In FIG. 6, the linear repeaters 60 and 70 are connected to face each other, and the OSC 72 on the linear repeater 70 side is connected.
, The selector 61 of the linear repeater 60 has selected the clock of the opposing device. Further, the linear repeater 70 is in a state where the OSC clock is selected. At this time, when the linear repeater 70 is connected to the multiplex repeater and a reference clock is input from the clock supply device, the selector 71 of the linear repeater 70
Is switched with the highest priority to the clock extracted from the own device by the switching sequence e of FIG. 8B. At the same time, the selector 61 of the linear repeater 60 does not change the state from the state where the clock of the opposing device is selected. Therefore, the linear repeaters 60 and 70 synchronize with the reference clock of the multiplexing terminal equipment connected to the linear repeater 70.

In FIG. 6, when the linear repeaters 60 and 70 are connected to each other and operate based on the OSC 72 of the linear repeater 70, the selector 61 of the linear repeater 60
The clock of the opposing device 70 has been selected. Further, the linear repeater 70 is in a state where the OSC clock is selected. At this time, the selector 61 of the linear repeater 60
By the switching sequence e in (B), the clock is switched to the clock extracted from the own device with the highest priority. At the same time, the selector 61 of the linear repeater 60 selects the OSC clock according to the switching sequence c of FIG. 8B, and the transmitted clock and the received clock have different phases. Then, the clock of the opposing device 70 is selected. That is, the linear repeaters 60 and 70 synchronize with the reference clock of the multiplexing terminal equipment connected to the linear repeater 60.

The configuration and operation of the preferred embodiment of the optical transmission system according to the present invention have been described above in detail. However, it should be noted that such preferred embodiments are merely examples of the present invention and do not limit the present invention in any way. It will be readily apparent to those skilled in the art that various modifications can be made in accordance with the particular application without departing from the spirit of the invention.

[0035]

As will be understood from the above description, according to the optical transmission system of the present invention, the following remarkable practical effects can be obtained. First, when a transmission error occurs on one side of the linear repeater, the linear repeater operates in synchronization with the reference clock of the multiplexed terminal equipment on the other side, so that the monitoring control signal can be accurately obtained. Can be transmitted to The reason is,
The reference clock of the linear repeater is the clock from the own device,
This is because the configuration is such that a clock from the clock of the opposing device can be selected.

Second, in the regenerative repeater and the linear repeater, the self-oscillator of either the opposite regenerative repeater or the linear repeater is operated as a reference clock in a state where the multiplexing terminal device is not connected, so that monitoring is performed. Control signals can be transmitted accurately. The reason is that the reference clock of the regenerative repeater and the linear repeater can be selected from the clock from the own device, the clock from the clock of the opposite device and the clock from the self-oscillator, and has a phase monitoring circuit and a switching condition circuit. This is due to the configuration.

Third, the structure can be simplified. The reason is that the clock from the opposite device is distinguished from the clock synchronized with the network sent from the multiplexing terminal device or the clock sent from the regenerative repeater and the linear repeater, and the phase difference of the phase monitoring unit is determined. Because the configuration is realized by the detection circuit,
This is because the state of the opposing device can be determined without defining a fixed bit for information transfer.

[Brief description of the drawings]

FIG. 1 is a principle diagram of a clock system in an optical transmission system according to the present invention.

FIG. 2 is a detailed control diagram of a clock system when linear repeaters face each other.

FIG. 3 is a reference clock route diagram when the transmission path is normal in the optical transmission system of FIG. 1;

FIG. 4 is a reference clock route diagram at the time of a transmission line failure in the optical transmission system of FIG. 1;

FIG. 5 is a reference clock route diagram when constructing the optical transmission system.

FIG. 6 is a block diagram showing a detailed configuration of an optical transmission system according to the present invention.

FIG. 7 is an explanatory diagram of selector switching conditions at the time of basic operation in the linear repeater shown in FIG. 6;

8A and 8B are explanatory diagrams of selector switching conditions shown in FIG. 7, wherein FIG. 8A is a configuration diagram and FIG. 8B is a state transition diagram.

FIG. 9 is a basic configuration diagram of a general optical transmission system.

FIG. 10 is a configuration diagram of an optical transmission system when a linear repeater is inserted.

11 is a configuration diagram of the linear repeater shown in FIG.

FIG. 12 is a principle diagram of a clock system in the repeater.

FIG. 13 is a detailed control diagram of a clock system of the linear repeater.

FIG. 14 is a detailed diagram of a clock system when linear repeaters face each other.

FIG. 15 is a basic configuration diagram of a conventional optical repeater monitoring system.

[Explanation of symbols]

10, 20 Multiplexing terminal equipment (LT-MUX) 12, 14, 22, 24 Multiplexing unit 15, 25 Reference clock generator 30, 40, 50 Regenerative repeater (REP) 32, 34, 42, 44, 61 , 71 selector (SE
L) 33, 43, 66, 76 Clock extraction unit 36, 38, 46, 48, 56, 58, 62, 72 Clock generator (OSC) 60, 70 Linear repeater 63, 73 Phase monitoring unit 64, 74 Multiplexer ( MUX)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04B 17/02 H04B 9/00 B H04J 3/08 F term (Reference) 5K002 AA05 AA05 CA13 DA01 DA05 EA05 FA01 5K028 AA14 BB08 NN32 PP11 5K042 AA08 CA10 CA15 DA21 FA01 FA15 JA01 5K047 AA11 BB02 CC02 GG02 GG09 GG45 KK03 KK15 MM49

Claims (6)

[Claims] 1. An optical transmission system in which one or more repeaters are connected between multiplexing terminal devices each having a multiplexing unit and a reference clock generator, wherein the repeaters include a clock switching selector and an internal clock. Wherein the selector selects the internal clock from the clock oscillator or the reference clock from the reference clock generator of the multiplexing terminal device. 2. The optical transmission system according to claim 1, wherein said repeater is a regenerative repeater or a linear repeater. 3. When the multiplexing terminal device is not connected and only a repeater-to-repeater having no reference clock is connected, priority is given to the opposing repeaters, and one of the opposing repeaters is assigned a priority. The optical transmission system according to claim 1, wherein the optical transmission system operates using the clock oscillator as a reference clock. 4. The repeater according to claim 1, further comprising: a clock extracting unit that extracts a clock from a device facing the unit, and a phase monitoring unit that monitors a phase of a clock selected and output by the selector. 4. The optical transmission system according to 2 or 3. 5. The optical transmission system according to claim 1, wherein said selector is switched according to a predetermined switching condition. 6. Each of the repeaters includes a west side and an EAS side.
A T-side clock oscillator;
6. The light according to claim 1, wherein an operation time of the selector is changed depending on whether the operation is performed on one side or the EAST side, and which clock oscillator operates between the opposing devices is determined as a reference. Transmission system.