JP2002359629A - Distance measurement method and program in atm-pon system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the occupancy of a band by a distance measurement window generated in a distance measurement operation to the utmost and to ensure the reliabil ity of a result of the distance measurement. SOLUTION: When distance measurement processing is started, whether the starting results from an initial connection operation from application of an ONU (Optical Network Unit) power supply or from restarting after the ONU in an operating state has fallen into a fault state is discriminated, in restarting, number of times (SUC) for success to delay measurement is regarded to obtain one success and the processing is started, and a delay reference value (d0) is used for a delay in a preceding operating state. Then the distance measurement window is open, a PLOAM (Physical Layer Operation Administration and Maintenance) grant is sent, a PLOAM cell sent from the ONU is received and when the delay is obtained, the delay measurement result is set to (d). When the difference between the delays d and d0 is within a phase limit, the SUC is incremented. When the SUC reaches a maximum value (SUC- NUM) of number of delay measurement success times specified in advance, a delay adjustment instruction value is calculated from the measured delay and the distance measurement operation is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an OLT.
(Optical Line Terminal) and multiple optical subscriber units ON
A PON (Passive Optical Network) that connects to a U (Optical Network Unit) in a star configuration via an optical coupler
k) The present invention relates to a system, particularly to an ATM-PON system that performs communication based on ATM cells.

[0002]

2. Description of the Related Art ATM-PON systems are now being widely used as one means for economically increasing the capacity and speed of access networks using optical fibers. FIG. 3 shows an example of a subscriber access network of the ATM-PON system.

A subscriber access network of the ATM-PON system includes an OLT 1 and a plurality of optical subscriber units O.
NUs 2-1 to 2-3, an optical coupler 3, and an optical fiber connecting them. The OLT 1 is installed in a station building, the optical coupler 3 is installed in a subscriber's house, an apartment house, a building, or the like remote from the station building, and a plurality of ONUs 2-1 to 2-3 are installed.
To accommodate subscriber lines.

Downlink cells to be transmitted from the OLT 1 to a plurality of ONUs 2-1 to 2-3 connected to the optical coupler 3 are multiplexed on the same optical fiber transmission line, transmitted to the optical coupler 3, and transmitted to the optical coupler 3. All ONUs 2-1 connected to
Each ONU is configured to extract only cells destined for itself and discard cells destined for other ONUs.

On the other hand, when cells are transmitted from each ONU to the OLT 1, since each upstream cell transmitted from a plurality of ONUs 2-1 to 2-3 joins at the optical coupler 3, the cells are transmitted from different ONUs. In order to prevent collision between cells, uplink cells from each ONU are time-division multiplexed.

[0006] At this time, in the ATM-PON system, in order to time-division multiplex upstream cells transmitted from a plurality of ONUs 2-1 to 2-3 installed at various distances, the ATM-PON system is turned on.
It is necessary to adjust the cell transmission timing on the U side,
Therefore, it is necessary to measure the distance from the OLT 1 to each of the ONUs 2-1 to 2-3.

This distance measurement is performed, for example, in Japanese Patent Application Laid-Open No. 2001-7.
As described in Japanese Patent Application Laid-Open No. 832, there is provided a timing called a distance measurement window in which cells are not transmitted from any ONU in the upstream direction.
And send the ONU for this PLOAM grant
This is performed by measuring the delay time until the PLOAM cell is returned from.

FIG. 2 is a flowchart showing a processing procedure of a conventional distance measuring operation. Hereinafter, a conventional distance measuring operation will be described with reference to FIG.

When the distance measurement process is started (f1), a distance measurement window is opened and PLAOM g is opened.
send (f4), and P sent from ONU
If the delay value can be obtained by receiving the LOAM cell, the delay measurement result is set to d (f4, f5).

If the number of successful delay measurements (SUC) is not 0, the current delay measurement result (d) and the delay reference value (d0)
Is confirmed to be within the allowable value (phase_limit), and the number of successful delay measurements (SUC) is counted (f).
7, f13, f9).

The number of successful delay measurements (SUC) is the maximum value (SUC_NU) of the predetermined number of successful delay measurements.
M), the delay adjustment instruction value is calculated from the measured delay value, and the distance measurement operation ends (f10, f11, f).
12).

In the case of failure, the number of times (FAIL) is counted up by +1. If the number reaches the maximum value (FAIL_NUM) of the number of delay measurement failures, the distance measurement operation is failed (f15, f16, f17).

When the difference between the current delay measurement result (d) and the delay reference value (d0) is larger than the allowable value (phase_limit), the delay reference value (d0) is obtained based on the current delay measurement result (d). ) Is updated, the count value (SUC) of the number of successful delay measurements is updated to 1 again, and the number of failed delay measurements (FAIL) is incremented by +1 (f1).
3, f14, f15).

As an example, the maximum value (S
A case where the system is operated with UC_NUM) being 2 will be described.

[0015] The distance measurement process starts, a distance measurement window is opened, and a PLAOMgrant is transmitted (f4). And PLOAM sent from ONU
The cell is received, and the obtained delay measurement result is set as d (f5, f
6).

When the first delay measurement is successful,
Since the number of successful delay measurements (SUC) is 0, the current delay measurement result (d) is used as the delay reference value (d0), and the number of successful delay measurements (SUC) is set to 1 (f7, f8,
f9). However, at this point, the SUC is SUC_NUM =
Since the distance does not reach 2, the distance measurement window is opened again and the PLAOM grant is transmitted. Let the delay measurement result obtained here be d (f4, f5).

The number of successful delay measurements (SUC) is now 0
(Count value = 1), the difference between the current delay measurement result (d) and the delay reference value (d0) is an allowable value (phase_li).
mit), and counts the number of successful delay measurements (SUC) (f7, f13, f9).

Since the number of successful delay measurements (SUC) reaches the maximum value of the number of successful delay measurements (SUC_NUM = 2), a delay adjustment instruction value is calculated from the measured delay value.
The distance measurement operation ends (f10, f11, f12).

As described above, in the conventional distance measurement operation, the reliability of the distance measurement result is ensured by once again performing the delay measurement on the result of the delay measurement and comparing the results.

[0020]

In the conventional distance measurement,
In order to measure the distance of one ONU, it is necessary to open the distance measurement window at least twice, but while the window is opened to perform the distance measurement, the bandwidth of the PON in the upstream direction is limited by the system itself. Will be occupied by
During that time, no ONU can transmit cells in the upstream direction.

For this reason, if the number of times the window is opened for performing the distance measurement increases, the bandwidth that each ONU can use for cell transmission decreases, and the transmission efficiency decreases accordingly.

An object of the present invention is to provide an AT
It is an object of the present invention to provide a distance measuring method that can reduce the occupation of a band by a distance measuring window generated when performing a distance measuring operation in an M-PON system as much as possible, and can ensure the reliability of the distance measuring result.

[0023]

As described above, the conventional A
In the distance measurement operation performed in the TM-PON system, first, delay measurement is performed once, and the delay measurement is again performed using the delay measurement as a reference delay value. For example, the reliability of the measurement result is ensured by using the value as a result of the delay measurement.

Therefore, when the ONU in a certain operation state is deactivated from the operation state due to some kind of failure, if the distance information measured before the failure can be used as the first distance information, the distance measurement window Can be reduced by one, and the same reliability as conventional distance measurement can be ensured.

According to the present invention, an ONU that has been in an operation state is deviated from the operation state due to some failure, and the ONU is
The distance measurement operation when the LT is restarted is treated separately from the initial connection operation from power ON, and in the case of the former, attention is paid to the fact that the possibility that the distance to the ONU suddenly changes is low, The number of times the distance measurement window is opened is reduced by one by using the delay value used up to the operation state immediately before the occurrence of the failure as the reference delay value.

As a result, the number of times the distance measurement window is opened when the ONU is restarted can be reduced by one per ONU. In other words, the system is PON for one delay measurement
Time occupying the upstream bandwidth can be reduced.
Therefore, there is an advantage that the influence on the band used by other ONUs can be reduced as compared with the conventional method, and the reliability of the measurement result can be assured as before.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a flowchart showing a procedure of a distance measuring operation according to the present invention. Also, FIG.
It is an example of an ATM-PON system to which the distance measuring method of the present invention is applied.

As described above, in the ATM-PON system, in order to time-division multiplex the upstream cells transmitted from a plurality of ONUs installed at different distances, distance measurement is performed and the timing at which the ONU transmits cells is determined. If not adjusted, cells will collide and communication will not be possible.

Therefore, in the distance measurement operation, the OLT opens the distance measurement window, and simultaneously sets the PLOAM grand.
Send t. The ONU responds to the PLOAM grant and returns a PLOAM cell. The distance measurement window refers to a timing at which the cell is not transmitted from any ONU in order to receive the upstream PLOAM cell whose timing is unknown.

OLT is PLOA sent from ONU.
The M cell is received, and the delay after grant is measured. The OLT calculates a delay adjustment value from the delay measurement result, and instructs the ONU to this value. Then, the ONU generates an uplink cell transmission timing according to the delay adjustment instruction value. In the ATM-PON system, by such a mechanism, uplink cells transmitted from a plurality of ONUs installed at various distances are prevented from overlapping in time.

The present invention makes it possible to reduce the number of times the distance measurement window is opened by adopting the processing procedure shown in FIG. 1 in the distance measurement. Hereinafter, the distance measuring operation according to the present invention will be described with reference to FIGS.

When the distance measurement process is started, the OLT
The processing device on the first side determines whether the operation is an initial connection operation from ONU power ON or a restart after the ONU in the operation state is removed from the abnormal state. In the case of the restart, the delay measurement is successful. The process is started by assuming that the number of times (SUC) has succeeded once, and the delay reference value (d0) is set as the delay value in the previous operation state (f2, f3).

Next, while opening the distance measurement window,
The PLAOM grant is transmitted (f4), the PLOAM cell transmitted from the ONU is received, and if a delay value can be obtained, the delay measurement result is set to d (f5, f
6).

If the number of successful delay measurements (SUC) is not 0, the current delay measurement result (d) and the delay reference value (d0)
Is confirmed to be within the allowable value (phase_limit), and the number of successful delay measurements (SUC) is counted (f).
7, f13, f9).

The number of successful delay measurements (SUC) is the maximum value (SUC_NU) of the predetermined number of successful delay measurements.
M), the delay adjustment instruction value is calculated from the measured delay value, and the distance measurement operation ends (f10, f11, f).
12).

In the case of failure, the number of times (FAIL) is counted, and if the maximum number (FAIL_NUM) of delay measurement failures is reached, the distance measurement operation fails (f15, f16, f17).

When the difference between the current delay measurement result (d) and the delay reference value (d0) is larger than the allowable value (phase_limit), the delay reference value (d0) is obtained based on the current delay measurement result (d). ) Is updated, the count value (SUC) of the delay measurement success count is updated to 1, and the delay measurement failure count (FAIL) is incremented by +1 (f13,
f14, f15).

As an example, a case where the system is operated with the maximum value of the number of successful delay measurements (SUC_NUM) set to 2 will be described.

First, the distance measurement operation will be described for the case of the initial connection operation after the ONU power is turned on.

When the distance measurement processing is started and it is determined that the operation is an initial connection operation after the ONU is turned on, the processing is started by setting the number of successful delay measurements (SUC) to 0 (f2).

Next, while opening the distance measurement window,
A PLAOM grant is transmitted (f4). And O
The PLOAM cell transmitted from the NU is received, and the obtained delay measurement result is set as d (f5, f6).

Since the number of successful delay measurements (SUC) is 0, the number of successful delay measurements (SUC) is counted using the present delay measurement result (d) as the delay reference value (d0) (f7, f8, f9). . But SUC is SUC_NUM
= 2, the distance measurement window is opened again and the PLAOM grant is transmitted. Let the delay measurement result obtained here be d (f4, f5).

Since the number of successful delay measurements (SUC) is not 0, the current delay measurement result (d) and the delay reference value (d0)
Is confirmed to be within the allowable value (phase_limit), and the number of successful delay measurements (SUC) is counted (f).
7, f13, f9).

Since the number of successful delay measurements (SUC) reaches the maximum value of the number of successful delay measurements (SUC_NUM = 2), a delay adjustment instruction value is calculated from the measured delay value.
The distance measurement operation ends (f10, f11, f12).

That is, in this case, the distance measurement window is opened at least twice as in the conventional example. Performing the delay measurement twice in this manner increases the reliability of the measured value.

Next, a description will be given of a measurement operation in the case where the ONU once in the operating state is restarted after being removed from the abnormal state.

If the distance measurement processing is started and it is determined that the ONU in the operating state is restarted after being out of the abnormal state, the processing apparatus for distance measurement determines the number of successful delay measurements (SUC). The processing is started assuming that the operation has succeeded once, and the delay reference value (d0) is set as the delay value used in the previous operation state (f2, f3).

Next, a distance measurement window is opened and P
The LAOM grant is transmitted (f4). If a PLOAM cell transmitted from the ONU is received and a delay value can be obtained, the delay measurement result is set to d (f4, f5).

Since the number of successful delay measurements (SUC) is 1, it is confirmed that the difference between the current delay measurement result (d) and the delay reference value (d0) is within an allowable value (phase_limit). (SUC) is counted (f
7, f13, f9).

Since the number of successful delay measurements (SUC) reaches the maximum value of the number of successful delay measurements (SUC_NUM = 2), a delay adjustment instruction value is calculated from the measured delay value d, and the distance measurement operation ends. (F10, f11, f1
2).

In other words, in this case, it is considered that the connection state of the ONU has not changed since it was in the previous operation state, so the delay value in the previous operation state should be used as the reference delay value. Thus, the processing can be completed with one distance measurement.

Therefore, when the number of connected ONUs is large, the number of times of setting the distance measurement window can be greatly reduced, and the transmission efficiency of uplink cells can be increased. In addition, the delay value in the previous operation state is used as a reference delay value and compared with the current delay measurement value to confirm that the delay value is equal to or within the allowable range.
This is equivalent to performing the measurement twice, and the reliability of the measured value can be secured.

Note that the distance measurement according to the present invention is performed by an in-station device (OL).
T) It can be executed by a processing means (computer) provided in 1, and the processing means stores a program for executing the present invention.

[0054]

According to the present invention, the distance measurement operation at the time of the initial connection after the power is turned on and the distance measurement operation at the time of the restart from the abnormal state are treated separately. Since the delay value in the state is used, the number of times of opening the distance measurement window can be reduced by one, and the reliability of the distance measurement result can be secured as before.

As a result, it is possible to reduce the occupation of the upstream band caused by opening the distance measurement window by the system without impairing the reliability of the distance measurement result, and to reduce the influence on the band used by other ONUs. can do.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a conventional example.

FIG. 3 is a diagram showing an outline of a PON system to which the present invention is applied.

[Explanation of symbols]

 1 OLT (Optical Line Terminal) in the office 2 Optical ONU (Optical Network Unit) 3 Optical coupler

Claims (4)

[Claims] 1. A distance measuring method in a PON system in which an OLT and a plurality of optical network units (ONUs) are connected in a star configuration between the OLT and the plurality of ONUs via an optical coupler. Before starting the distance measurement processing, the start of the distance measurement processing is activation by an initial connection operation from ON power ON, or restart after the ONU in the operation state is removed from the abnormal state. When the restart is determined, the delay measurement value in the previous operation state is set as the delay reference value, and the count value of the number of successful delay measurements is set to 1
To open the distance measurement window and set the PLAOM
send grant and PLOA sent from ONU
When the delay value is obtained by receiving the M cell, a delay measurement result is output, and the difference between the current delay measurement result and the delay reference value is confirmed to be within an allowable value, and the delay measurement success count is determined. After incrementing the count value of +1 by one, the distance measurement window is opened again and the distance measurement is repeated, and when the count value of the number of successful delay measurements reaches the predetermined number of successful delay measurements, the delay is adjusted from the delay value. A distance measuring method in a PON system, comprising calculating an indicated value. 2. When it is determined that the start of the distance measurement process is an activation by an initial connection operation from ONU power ON, the distance measurement window is immediately opened to open the P
A LAOM grant is transmitted, the PLOAM cell sent from the ONU is received, a delay measurement result is output when a delay value is obtained, and the delay measurement result is output when the count value of the number of successful delay measurements is 0. Is held as a delay reference value, and the count value of the number of successful delay measurements is set to 1, and when the count value of the number of successful delay measurements is not 0, the difference between the current delay measurement result and the delay reference value is within an allowable value. 2. The distance measuring method according to claim 1, wherein the count value of the number of successful delay measurements is incremented by +1 after confirming that: 3. A distance measurement is performed in an intra-office device (OLT), a plurality of optical subscriber units (ONUs), and a PON system that connects the OLT and the plurality of ONUs in a star configuration via an optical coupler. A step of starting a distance measurement process and a step of starting the distance measurement process are started by an initial connection operation from ON power ON, or turned ON in an operation state.
A step of judging whether or not the restart has occurred after U has gone out of the abnormal state; and, if it has been judged that the restart has occurred, the delay measurement value in the previous operation state is set as a delay reference value and the number of times of delay measurement success Setting the count value to 1 and opening the distance measurement window and setting the PLAOM gr
transmitting a PLOAM cell sent from the ONU and outputting a delay measurement result when a delay value is obtained; and calculating a difference between the current delay measurement result and the delay reference value. A step of counting up the count value of the number of successful delay measurements by confirming that it is within an allowable value by +1; a step of repeating the step of opening the distance measurement window and performing the distance measurement; A step of calculating a delay adjustment instruction value from the delay value when the count value reaches a predetermined delay measurement success count value.
A program for executing distance measurement in the ON system. 4. When it is determined that the activation of the step of starting the distance measurement processing is an activation by an initial connection operation from ONU power ON, a distance measurement window is immediately opened and the PLAOM grant is transmitted. Receiving a PLOAM cell sent from an ONU and outputting a delay measurement result when a delay value is obtained, and, when the count value of the number of successful delay measurements is 0, using the delay measurement result as a delay reference value And setting the count value of the number of successful delay measurements to 1; and when the count value of the number of successful delay measurements is not 0, the difference between the current delay measurement result and the delay reference value is within an allowable value. Confirming that the delay measurement has succeeded, and counting up the count value of the number of successful delay measurements by +1. Program for executing the distance measurement in a PON system 3 according.