JP2000341311A - Optical access changeover system for optical subscriber line terminator and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid replacement of a terminator even when the communication system is changed from the PDS system to the SS system or vice versa and to eliminate the need for replacing the terminator even when the communication system is changed from the PDS system to the SS system or vice versa. SOLUTION: The optical access changeover switch system for an optical subscriber line terminator to make optical access to an installation center, is provided with single star transmission/reception circuits 103, 202 that attain optical access of single star, passive double star transmission/reception circuits 104, 203 that access optical access by passive double start and a subscriber signal identification circuit 102. Thus, the subscriber signal identification circuit 102 identifies synchronizing signals different from each other and used by the optical access of single star and the optical access of passive double star as to the subscriber input signal sent from the installation center to alternatively select the single star transmission/reception circuit or the passive double star transmission/reception circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical network unit. In particular, the present invention relates to SS (Single Sta)
r: single star, PDS (passive)
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical access switching system and method for an optical network unit that facilitates switching between a Double Star (Passive Star) system.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing a configuration of an SS system and a PDS system. As shown in the figure, the optical access system includes an SS (Single Star; Single Star) system and a PDS (Passive Double Sta).
r; passive double star) system. This figure (a)
As shown in FIG. 1, in the SS system configuration, the optical network unit (ONU; Opt;
The optical fiber 402 is laid in a one-to-one star shape on the I.C. This SS
In the scheme, one subscriber occupies one optical fiber.

As shown in FIG. 1B, in the configuration of the PDS system, an optical branching element 404 is provided between an equipment center 401 and an optical network unit 403 as a subscriber.
The optical splitter 404 splits and combines optical signals. An optical fiber 402 for multiplexing a signal is laid between the equipment center 401 and the optical branching element 404, and each optical fiber is connected between the optical branching element 404 and the optical network unit 403 as in the SS system. Optical fiber 4 for each subscriber line termination device 403
02 is laid. In this PDS system, the equipment center 4
Many subscribers from 01 to the optical branching element 404 share one optical fiber from the standpoint of effective use of the optical fiber.
At present, in order to realize low cost, an optical access system of the PDS system is becoming the center. On the other hand, the SS system is also mixed for the reason that a large band is required.

[0004]

[Problems to be solved by the invention] By the way, in the future, PD
If the bandwidth required by S-type subscribers increases, PDS
In the case of the system, since the band per optical fiber of the PDS system is determined, it becomes difficult to accommodate many subscribers with one optical fiber. For this reason,
In the future, it is expected that it will be necessary to change the PDS system to the SS system. However, the current optical network unit of the PDS system and the optical network unit of the SS system are completely different devices, and when changing from the PDS system to the SS system, the optical network unit is required. There is a problem that the device itself must be replaced for each device.

[0005] Further, when it is desired to temporarily switch to the SS system and return to the PDS system for some reason, it is necessary to replace the optical network unit itself for each device. Therefore, the present invention has been made in view of the above-mentioned problems, and therefore, even if the PDS system is changed to the SS system and conversely, the SS system is changed to the PDS system, there is no need to replace each device. It is an object to provide an access switching system and method.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention enables a single-star optical access in an optical access switching system of an optical network unit for optical access to an equipment center. A single-star transmitting / receiving circuit, a passive double-star transmitting / receiving circuit that enables passive double-star optical access, and the single-star optical access, the passive double, for a subscriber input signal transmitted from the facility center. And a subscriber signal identification circuit for selectively selecting a transmission / reception circuit for a single star or a transmission / reception circuit for a passive double star by identifying different synchronization signals used in optical access of a star. An optical access switching system for an optical network unit is provided.

By this means, even if the PDS system is changed to the SS system, and conversely, the SS system is changed to the PDS system,
There is no need to replace each device. That is, there is no need to prepare two types of devices, and switching can be automatically performed.
It is not necessary to go to the subscriber to switch the maintenance staff, and the maintenance cost can be reduced. Preferably, a synchronous digital hierarchy system is used for the single-star optical access, an asynchronous transfer mode system is used for the passive double-star optical access, or an asynchronous transfer mode system is used for the single-star optical access. A synchronous digital hierarchy method is used for the passive double star optical access.

By this means, SDs with different synchronization
Since the H system and the ATM system are used, it is possible to switch between the single star optical access and the passive double star optical access. Preferably, when the synchronous digital hierarchy method is used for the optical access, the subscriber signal identification circuit detects frame synchronization by comparing bit strings of A1 and A2 bytes in a regenerator section overhead, and asynchronously transfers the frame to the access. When the mode method is used, the cell synchronization is detected by the HEC function of the cell header.

By this means, the frame period of the synchronous digital hierarchy system is 125 μs, and the cell synchronization period of the asynchronous transfer mode system is 2.7 μs.
Different synchronizations can be identified. Preferably, the cell synchronization detection is performed including detection of synchronization of a physical layer maintenance operation management cell inserted in the cell. By this means, the physical layer maintenance operation management cell is also included in the synchronization detection, so that synchronization is easily established, and synchronization is hardly lost.

Further, the present invention relates to a method for optical access switching of an optical network unit for optical access to an equipment center, comprising the steps of: performing single-star optical access to a single-star transmitting / receiving circuit; Performing a passive double star optical access to the transmitting and receiving circuit, and for a subscriber input signal transmitted from the equipment center, the single star optical access, a different synchronization signal used in the passive double star optical access. Discriminating and selectively selecting a transmission / reception circuit for a single star or a transmission / reception circuit for a passive double star. By this means, there is no need to replace each device even when the PDS system is changed to the SS system and conversely, the SS system is changed to the PDS system. That is, there is no need to prepare two types of devices, and switching can be performed automatically. Therefore, it is not necessary to go to the subscriber to switch, and maintenance costs can be reduced.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram showing an optical line terminal according to the present invention. As shown in the figure, an optical network unit (ONU; Optical)
al Network Unit) 403 has O / E
An (optical / electrical) conversion circuit 101 is provided. The O / E conversion circuit 101 converts a subscriber optical input signal 1 into an electric signal from a terminal A connected to the optical fiber 402 and outputs a subscriber signal 2.

The subscriber optical input signal 1 is a downlink signal from the equipment center (see FIG. 5) 401 to the optical network unit 403. The O / E conversion circuit 101 includes a subscriber signal identification circuit 102, an SS (Single Star; single star) receiving circuit 103, and a PDS (Passive).
Double Star (Passive Double Star) receiving circuit 104 is connected. Subscriber signal identification circuit 102
Performs a subscriber signal 2 identification process and outputs a subscriber signal identification signal 3.

The SS receiving circuit 103 converts the subscriber signal 2 to SS
The reception processing is performed and the SS reception signal 4 is output. The PDS receiving circuit 104 performs a PDS receiving process on the subscriber signal 2 to perform a PDS
The receiving signal 5 is output. A reception selection circuit 105 and a transmission selection circuit 204 are connected to the subscriber signal identification circuit 102. A reception selection circuit 105 is connected to the SS reception circuit 103 and the PDS reception circuit 104, and the reception selection circuit 105
The SS reception signal 4 and the PDS reception signal 5 are selectively processed and a selected reception signal 6 is output.

The reception selection circuit 105 includes a subscriber reception circuit 1
The subscriber reception circuit 106 processes the selected reception signal 6 and outputs a subscriber reception signal 7 to a terminal C. The terminal C is connected to a subscriber interface. Next, a subscriber transmitting circuit 201 is connected to the terminal D, the subscriber transmitting circuit 201 processes the subscriber transmitting signal 8 input from the terminal D, and terminates the interface on the subscriber side.
An output signal 9 is output. SS is included in the subscriber transmission circuit 201.
The transmission circuit 202 and the PDS transmission circuit 203 are connected,
The S transmission circuit 202 converts the output signal 9 into the format of the SS system, outputs the SS transmission signal 10,
The S transmission circuit 203 converts the output signal 9 into a PDS system format and outputs a PDS transmission signal 11.

SS transmission circuit 202, PDS transmission circuit 20
3, a transmission selection circuit 204 is connected.
04 selects the SS transmission signal 10 and the PDS transmission signal 11 and outputs a selected transmission signal 12. Transmission selection circuit 20
4 is connected to an E / O (electric / optical) conversion circuit 205,
The E / O conversion circuit 205 converts the selected transmission signal 12 into an optical signal and outputs a subscriber optical output signal 13 to a terminal B connected to the optical fiber 402. The subscriber optical output signal 13
Is an upstream signal from the optical network unit 403 to the equipment center 401 (see FIG. 5).

FIG. 2 is a schematic block diagram illustrating a configuration example of the subscriber signal identification circuit 102 of FIG. As shown in the figure, an SS frame synchronization detection circuit 301 and a PDS frame synchronization detection circuit 302 are provided on the input side of the subscriber signal identification circuit 102, and each receives a subscriber signal 2. S
The S frame synchronization detection circuit 301 detects the SS from the subscriber signal 2
A process for detecting frame synchronization is performed, and an SS frame synchronization detection signal 21 is output. The PDS frame synchronization detection circuit 302 performs a process of detecting PDS frame synchronization from the subscriber signal 2 and outputs a PDS frame synchronization detection signal 22. The SS frame synchronization detection circuit 301 and the PDS frame synchronization detection circuit 302 are provided with a subscriber signal determination circuit 303 on the output side, and the subscriber signal determination circuit 303 determines the SS frame synchronization detection signal 21 and the PDS frame synchronization detection signal 22. The processing is performed to output the subscriber signal identification signal 3.

FIG. 3 is a diagram for explaining the subscriber optical input signal 1 or the subscriber optical output signal 13 of FIG. The subscriber optical input signal 1 of the O / E conversion circuit 101 and the subscriber optical output signal 13 of the E / O conversion circuit 205 determine whether the access network to be synchronized is SS.
In the case of the system, generally, SDH (Synchronous)
When an optical transmission format of Digital Hierarchy (Synchronous Digital Hierarchy) is used and an access network to be synchronized is a PDS system, ATM (Asy) is used.
An optical transmission format of an nchronous transfer mode (asynchronous transfer mode) is used.

As shown in FIG. 3A, in the SDH method, one frame is represented by a two-dimensional byte array of 9 rows and 270 columns, and the first 9 rows and 9 bytes include a section overhead (SOH) and the like. , The next 261 bytes in 9 rows are called a payload containing multiplexed information. The section overhead is provided with a regenerator section overhead (RSOH), and the regenerator section overhead is provided with A1 and A2 bits as fixed bits for establishing frame synchronization. Also, the frame period is set to a transfer rate of 1
If it is 55.52 Mb / s, it will be 125 μs.

As shown in FIG. 3B, in the ATM system, information is divided and multiplexed and transferred into cells of a fixed-length block of 53 bytes. One cell is composed of a 5-byte header and a 48-byte cell. And information data. In addition,
The cell cycle is 2.7 μs when the transfer rate is 155.52 Mb / s. In the ATM system, a header of a cell is HEC (Header Error Controller).
ol; header error control) function, and cell synchronization is required by the HEC function.

The SS frame synchronization detecting circuit 30 shown in FIG.
No. 1 collates the bit strings of A1 and A2 bits of the generator section overhead in SDH. If the collation matches, the SS frame synchronization detection circuit 301
The S frame synchronization detection signal 21 is set to a high (high) level. The PDS frame synchronization detection circuit 302 shown in FIG.
Uses the HEC function of the cell header in FIG.
The PDS frame synchronization detection signal 22 is obtained as follows.

The HEC function includes a CRC (Cyclic Redundan) that detects and corrects a header error in the last one byte of the five bytes of the header in the cell.
A cyCheck (cyclic redundancy code) operation function is provided. That is, the received bit is temporarily regarded as the head bit of the cell, the CRC operation is performed on the 4 bytes (32 bits) by shifting one bit at a time, and the result is compared with the value of the 5th byte (hunting state). It is assumed that the calculation is repeated while shifting the leading bit one bit at a time as it is, and that the matching result indicates that the leading position of the cell has been identified (quasi-synchronous state).

Next, a CRC operation is performed on the next 4 bytes every 53 bytes, and the CRC is checked against the value of the 5th byte. Once the synchronization is established, even if there is an error in the CRC calculation, the synchronization is not immediately lost, and the error returns to the above-mentioned hunting state only after an error has occurred consecutively M times.
The ATM cells include PLOAM (Physical L).
eyer Operations, Administr
An insertion and maintenance (physical layer maintenance and operation management) cell is inserted. The synchronization is also detected for the PLOAM cell.

When cell synchronization is established, the PDS frame synchronization detection circuit 302
To a High level. As described above, the subscriber signal identification circuit 102 uses the difference between the frame synchronization detection of the SS system and the frame synchronization detection of the PDS system to determine whether the signal is an SS system signal or a PDS system signal. Is performed. FIG. 4 is a flowchart illustrating an operation example of the subscriber signal identification circuit 102. As shown in the figure, in step S1, the subscriber signal identification circuit 102 inputs the subscriber signal 2. Step S2
Here, the SS frame synchronization detection circuit 301 performs the process of detecting the SS frame synchronization.

In step S3, the PDS frame synchronization detection circuit 302 performs a PDS frame synchronization detection process. In step S4, it is determined whether SS frame synchronization has been detected. In step S5, P
It is determined whether DS frame synchronization has been detected. In step S6, when SS frame synchronization is detected in step S4, the SS frame synchronization detection signal 21 is set to a high (high) level. Proceed to step S10.

In step S7, P in step S5
When DS frame synchronization is detected, the PDS frame synchronization detection signal 22 is set to High level. In step S8, if SS frame synchronization is not detected in step S4, the SS frame synchronization detection signal 21 is set to L level.
ow (low) level. Proceed to step S10. In step S9, if PDS frame synchronization is not detected in step S5, the PDS frame synchronization detection signal 22 is set to Low level. Proceed to step S11.

In step S10, the SS signal synchronizing detection signal 21 is set to Hig in the subscriber signal judgment circuit 303.
It is determined whether or not the level is the h level. When the SS frame synchronization detection signal 21 is at a high level, the subscriber signal identification signal 3 is set at a high level. Proceed to step S13. S
If the S-frame synchronization detection signal 21 is at the low level, the process ends. In step S11, the subscriber signal determination circuit 303 determines whether the PDS frame synchronization detection signal 22 is at a high level. If it is at the low level, the process ends.

In step S12, the subscriber signal determination circuit 303 sets the subscriber signal identification signal 3 to low level when the PDS frame synchronization detection signal 22 is high level in step S11. Proceed to step S13. In step S13, it is determined whether or not the subscriber signal identification signal 3 is at a high level. In step S14, the subscriber signal identification signal 3 is set to Hig in step S13.
In the case of the h level, the SS reception signal 4 is selected by the reception selection circuit 105. That is, the subscriber optical input signal 1
Is the signal of the SS system, the SS receiving circuit 103 is selected as the terminating circuit, the SS system is correctly terminated, and the subscriber reception signal 7 that terminates the SS system is output from the terminal C.

In step S15, the transmission selection circuit 2
04 selects the SS transmission signal 10. When the subscriber optical input signal 1 is a signal of the SS system, the SS transmission circuit 202 is selected as the transmission circuit, the conversion to the SS system is correctly performed, and the subscriber optical output signal 13 converted to the SS system is output from the terminal B. Is done. In step S16, if the subscriber signal identification signal 3 is at the low level in step S13, the PDS reception signal 5 is selected. When the subscriber optical input signal 1 is a signal of the PDS system, the PDS receiving circuit 104 is selected as the termination circuit, the termination of the SS system is correctly performed, and the subscriber reception signal 7 that terminates the PDS system is output from the terminal C. You.

In step S17, the transmission selection circuit 2
04 selects the PDS transmission signal 11. When the subscriber optical input signal 1 is a PDS system, P
The DS transmission circuit 203 is selected, the conversion to the PDS system is correctly performed, and the subscriber optical output signal 13 converted to the PDS system is output from the terminal B. In the above explanation,
The SS system uses the SDH system and the PDS system uses the ATM system.
The M system may be used, and the SDH system may be used for the PDS system.

[0030]

As described above, according to the present invention,
Switching from SS system to PDS system is also possible from PDS system to SS
Switching of the system does not require replacement of devices, so there is no need to prepare two types of devices, and switching can be performed automatically, so that maintenance personnel do not have to go to the subscriber to switch. Cost can be reduced. In addition, it is necessary to add a subscriber signal identification circuit, a reception selection circuit, a transmission selection circuit, and to have a PDS type termination circuit and an SS type termination circuit in duplicate, but since a logic circuit is added,
From the current LSI technology, the increase in cost can be ignored in consideration of the above effects.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing an optical network unit according to the present invention.

FIG. 2 is a schematic block diagram illustrating a configuration example of a subscriber signal identification circuit 102 in FIG.

FIG. 3 is a diagram illustrating a subscriber optical input signal 1 or a subscriber optical output signal 13 of FIG. 1;

FIG. 4 is a flowchart illustrating an operation example of a subscriber signal identification circuit 102;

FIG. 5 is a diagram showing a configuration of an SS system and a PDS system.

[Explanation of symbols]

 1 ... Subscriber optical input signal 2 ... Subscriber signal 3 ... Subscriber signal identification signal 4 ... SS reception signal 5 ... PDS reception signal 6 ... Selection reception signal 7 ... Subscriber reception signal 8 ... Subscriber transmission signal 9 ... Output signal DESCRIPTION OF SYMBOLS 10 ... SS transmission signal 11 ... PDS transmission signal 12 ... Selection transmission signal 13 ... Subscriber light output signal 21 ... SS frame synchronization detection signal 22 ... PDS frame synchronization detection signal 101 ... O / E conversion circuit 102 ... Subscriber signal identification circuit 103 ... SS receiving circuit 104 ... PDS receiving circuit 105 ... Reception selecting circuit 106 ... Subscriber receiving circuit 201 ... Subscriber transmitting circuit 202 ... SS transmitting circuit 203 ... PDS transmitting circuit 204 ... Transmission selecting circuit 205 ... E / O conversion circuit 301 ... SS frame synchronization detection circuit 302 ... PDS frame synchronization detection circuit 303 ... subscriber signal judgment circuit 401 ... facility center 402 … Optical fiber 403… Optical subscriber line termination A, B, C, D… Terminal

Claims (6)

[Claims] 1. An optical access switching system for an optical line terminal for optical access to an equipment center, comprising: a single-star transmission / reception circuit enabling single-star optical access; and a passive double-star optical access. A passive double-star transmission / reception circuit that enables, for a subscriber input signal transmitted from the facility center, identifying the single-star optical access, different synchronization signals used in the passive double-star optical access, An optical access switching system for an optical network unit, comprising: a transmission / reception circuit for a single star or a transmission / reception circuit for a passive double star. 2. The optical system according to claim 1, wherein a synchronous digital hierarchy system is used for the single star optical access, and an asynchronous transfer mode system is used for the passive double star optical access. Optical access switching system for subscriber line termination equipment. 3. The optical device according to claim 1, wherein an asynchronous transfer mode system is used for the single star optical access, and a synchronous digital hierarchy system is used for the passive double star optical access. Optical access switching system for subscriber line termination equipment. 4. The subscriber signal identification circuit, when using a synchronous digital hierarchy system for the optical access, a regenerator section overhead A1,
4. The method according to claim 2, wherein frame synchronization is detected by collating a bit string of A2 bytes, and when the asynchronous transfer mode is used for the access, cell synchronization is detected by an HEC function of a cell header. An optical access switching system for an optical network unit according to claim 1. 5. The optical network unit according to claim 1, wherein the cell synchronization detection includes detection of synchronization of a physical layer operation and maintenance management cell inserted in the cell. Optical access switching system. 6. An optical access switching method of an optical line terminal for optical access to an equipment center, comprising: a step of performing single-star optical access to a single-star transmission / reception circuit; Performing a passive double star optical access, and for a subscriber input signal transmitted from the equipment center, identifying the single star optical access, a different synchronization signal used in the passive double star optical access, Selectively selecting a transmission / reception circuit for a single star or a transmission / reception circuit for a passive double star.