JP2001268103A - Subscriber access system and station side device to be applied to the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a subscriber access system for effectively utilizing a receiving area by lowering the occupancy rate of an area to be secured by a station side device at the time of delay control. SOLUTION: A distance measuring part 11 prepares position information for specifying an area to receive a delay control cell and stores it in a storage part concerning each subscriber side device, to which delay time is set. When setting the delay time to the subscriber side device again, in order to receive the delay control cell, a distance measuring window generation instructing part 14 secures an area secured at the time of initial start or area specified from the position information according to setting of a distance measuring window width determining part 13. A distance measurement failure count part 12 counts the number of times of setting failure when setting the delay time again and the distance measuring window width determining part 13 changes frequency in the case of securing the same area as the time of initial start and in the case of securing the area specified from the position information corresponding to the number of times of failure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a subscriber access system for performing communication between a station side device and a plurality of subscriber side devices, and a station side device applied to the subscriber access system.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing an example of the configuration of a star configuration communication system in which an optical line terminal and a plurality of subscriber side devices are connected by a star coupler. In FIG. 7, the optical line terminal 30 and a plurality of subscriber side devices 2a to 2d are connected via a star coupler 3, and constitute a star configuration communication system. In the following description, the OLT is referred to as an OLT.
(Optical Line Terminal), and the ONU (Opt
ical Network Unit). Communication between the OLT 30 and each ONU is performed by a cell which is a unit of data. The cell has an area for storing data for transmission control and an area for storing data.
The cell transmitted in the direction (T direction) further includes a guard cell of the cell.
It has an area used for extraction. In addition, cells are classified into data cells, PLOAM cells, and the like according to their roles. The data cell is a cell that stores data to be transmitted, and the PLOAM cell is a cell that performs communication control (delay control, which will be described later, a request to send a cell in the uplink direction, and the like). Another cell is an IDLE cell for speed adjustment inserted when there is no information to be transmitted.

Normally, the transmission path distance between the OLT 30 and each of the ONUs 2a to 2d differs for each ONU. Therefore,
The OLT 30 transmits an upstream cell transmission request instructing a plurality of ONUs to transmit cells at the same time, and each ONU
When sending back to the LT 30, the timing at which the OLT 30 receives a cell differs. So, OLT
The 30 performs delay control according to the transmission path distance for each ONU so that cells transmitted from a plurality of ONUs arrive at the OLT 30 at the same timing.

[0004] The OLT 30 performs delay control as follows. However, in the ONU connected to the OLT 30,
The longest transmission path distance is Xkm, and the time for light to reciprocate Xkm is Teqd. Also, the internal delay time from when the ONU receives the uplink cell transmission request and returns the cell is
It is constant at U, and this internal delay time is defined as Tres.

[0005] The OLT 30 transmits an upstream cell transmission request to each ONU to control the PLOAM for delay control.
An instruction to send back the cell is issued, and each ONU
Send back the OAM cell. The time from when the OLT 30 issues the uplink cell transmission request to when the OLT 30 receives the PLOAM cell is:
For an ONU with a transmission path distance of X km, (Teqd + Tre
s), and for ONUs whose transmission path distance is 0 km, T
res.

The OLT 30 measures, for each ONU, the time from when an uplink cell transmission request is issued to when a PLOAM cell is received, and calculates the difference between the measured time and the measured time for the ONU whose transmission path distance is the longest Xkm. Is calculated. This difference is 0 for ONUs with a transmission path distance of X km and Teqd for ONUs with a distance of 0 km. OLT3
0, after calculating the difference for each ONU, gives an instruction to each ONU, "Hold for a time corresponding to the difference before sending out a cell." By delaying cell transmission in the ONU in this way, the OLT 30
Can make cells arrive at the same timing.
In the following description, calculating a time (difference) to be delayed and giving a delay instruction to each ONU is referred to as “perform distance measurement”.

[0007] When measuring a distance, if a PLOAM cell and another cell are received in the same area, cell collision occurs and data is destroyed. Therefore, the OLT 30 has a plurality of ONUs.
Must secure an area for receiving the PLOAM cell returned from the. When the OLT 30 performs distance measurement for a plurality of ONUs within X km, an area for Y cells must be secured. In order to secure the area, the OLT 30 assigns a cell that instructs not to transmit a cell to the reception area of the PLOAM cell used for delay control to all O
It is transmitted to the NU in advance. Information indicating this instruction is "una
By transmitting one "unassigned grant", transmission to an area corresponding to one cell is not performed.In the above example, the OLT 30 transmits "u" to each ONU.
By transmitting Y “nassigned grants”, an area for Y cells is secured. After securing the area, an instruction to send back a PLOAM cell for delay control is issued to avoid cell collision in this area. be able to.

An area for receiving a PLOAM cell used for delay control is called a “distance measurement window”, and instructing not to transmit cells in the uplink direction to secure an area is called “open a distance measurement window” or "Create a distance measurement window."

Since it takes a time (Teqd + Tres) from transmission of an upstream cell transmission request to the furthest ONU at a distance X km to reception of a PLOAM cell, the OLT 30
Opens a distance measurement window during this time. in this way,
By securing an area for Y cells during (Teqd + Tres), PLOAM cells can be received from each ONU within the Xkm range. In the conventional star configuration optical communication system, the secured area is always the same area without distinction at the time of initial connection or restart.

[0010]

However, with respect to the area secured for the distance measurement, data cells and the like cannot be transmitted in the upstream direction. Therefore,
Of the secured areas, areas other than the area that actually receives the PLOAM cell are not effectively used and are wasted.

When the ONU enters the non-operating state due to a power failure or a transmission line failure, and the OLT 30 attempts to activate the ONU again to transition to the operating state, the OLT 30
Measures the distance while securing the same area as at the time of the initial connection.
If the failure of the distance measurement due to a transmission path failure or the like is repeated in the distance measurement at the time of the restart, the area for the distance measurement is occupied for a long time and cannot be used effectively.

The present invention provides a PLOA secured during delay control.
It is an object of the present invention to provide a star configuration communication system capable of reducing the occupation rate of an M cell reception area and effectively using the area, and a station apparatus applied to the star configuration communication system.

[0013]

A subscriber access system according to the present invention is a subscriber access system in which a station apparatus and a plurality of subscriber apparatuses are connected, wherein the station apparatus has a delay control cell. A cell transmission request for transmission is transmitted to each subscriber side device, and a delay in cell transmission to each subscriber side device based on a time from transmission of the cell transmission request to reception of a delay control cell. In a subscriber access system having delay control means for setting time, the optical line terminal creates area specifying information for specifying a reception area of a delay control cell for each of the optical network units for which a delay time has been set at the time of initial connection. It is characterized by comprising an area specifying information creating means.

Further, the station apparatus applied to the subscriber access system according to the present invention is connected to a plurality of subscriber apparatuses to form a subscriber access system, and issues a cell transmission request for instructing transmission of a delay control cell. Delay control means for setting a delay time at the time of cell transmission to each subscriber side device based on a time from transmission of a cell transmission request to each subscriber side device to reception of a delay control cell; An optical line terminal comprising: an area specifying information generating means for generating area specifying information for specifying a reception area of a delay control cell for each of the subscriber side apparatuses for which a delay time is set at the time of initial connection. I do. According to such a configuration, when the delay time is set again in the subscriber device, it is possible to realize a subscriber access system in which the occupancy of the reception area of the delay control cell is reduced and the area is effectively used. .

The delay control means, when receiving a delay control cell for setting a delay time again for the subscriber side apparatus which has set the delay time at the time of initial connection, specifies the same reception area and area as at the time of the initial connection. In this configuration, one of the reception areas specified by the information is selectively secured to receive the delay control cell. According to such a configuration, the occupation ratio of the reception area of the delay control cell can be reduced.

The delay control means sets the delay time again for the subscriber device for which the delay time was set at the time of the initial connection. And a frequency changing unit that changes the frequency of the case of securing the reception area specified by the area specifying information. According to such a configuration, when the setting of the delay time repeatedly fails, the occupancy of the reception area of the delay control cell can be changed.

For example, when the number of times that the setting of the delay time has failed exceeds a predetermined threshold value, the frequency changing means secures the same reception area as at the time of the initial connection and receives the reception area specified by the area specifying information. A configuration in which the frequency for securing the area may be changed.

The frequency changing means may be configured to increase the frequency of securing the reception area specified by the area specifying information when the setting of the delay time has repeatedly failed. According to such a configuration, the reception area of the delay control cell can be effectively used, and the delay control can be performed even when the installation position of the subscriber-side device greatly changes.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an optical line terminal applied to a subscriber access system according to the present invention. Although the star coupler 3 is omitted in FIG. 1 and only one ONU 2 is shown, the OLT shown in FIG.
1 is connected to a plurality of ONUs via a star coupler 3 as in the case shown in FIG. The OLT 1 includes a distance measuring unit 11 described below.
Distance measurement failure count unit 12, distance measurement window width determination unit 13, distance measurement window generation instructing unit 14
And

The distance measuring unit 11 transmits an uplink cell transmission request and receives a PLOAM cell for delay control from each ONU. Then, after transmitting the uplink cell transmission request, P
The distance to the ONU is measured based on the time until the LOAM cell is received (a delay instruction is given to the ONU). When the distance measurement fails due to a transmission path failure or the like, the information to that effect is notified to the distance measurement failure counting unit 12.

If the distance measurement is successful, the distance measurement unit 11 stores the transmission path distance from the OLT 1 to the ONU as position information (not shown in FIG. 1).
To memorize. The transmission path distance is measured in the distance measurement.
Time until M cell returns ".

The distance measurement failure counting unit 12
If the distance measurement to is continuously failed, the number of failures is counted. The initial value of the count value is 0, but when information indicating that the distance measurement has failed is obtained from the distance measurement unit 11, the count value is incremented. The distance measurement failure counting unit 12 has a plurality of thresholds such as thresholds P1, P2,... Each time the count value exceeds each threshold, distance measurement information is measured. Window width determination unit 1
Notify 3. Note that only one threshold may be provided.

Upon receiving a notification from the distance measurement failure counting section 12 that the count value has exceeded a predetermined threshold value, the distance measurement window width determination section 13 measures the width of the distance measurement window and the distance measurement of a plurality of types of widths. The window generation frequency is changed, and the change result is notified to the distance measurement window generation instructing unit 14.

The distance measurement window generation instructing unit 14 determines a plurality of types of ONUs based on the result of the change by the distance measurement window width determining unit 13 and the position information stored in the storage unit for the ONU for which the distance measurement has failed. Create a distance measurement window of width. The distance measurement unit 11 repeats the distance measurement using the distance measurement window in which the width and the frequency of occurrence have been changed.

In the example shown above, PLOAM cells are received from ONUs within X km by securing an area of Y cells for a time of (Teqd + Tres). Therefore, cell 1
For the individual area, the PLOAM cell can be received from the ONU within the range of X / Ykm by opening the distance measurement window for one cell for the time of (Teqd + Tres) / Y. For example, when an area of 9.6M is secured as an area for 69 cells and distance measurement is performed for ONUs within 20 km (that is, when the transmission path distance is 20 km).
When delay control is performed by calculating the delay times of a plurality of ONUs below, and the time from transmitting an uplink cell transmission request to an ONU having a transmission path distance of 20 km and returning a PLOAM cell is assumed to be approximately 200 μs, By opening the window for 200/69 = approximately 2.9 μs for the region of one cell, 20/69 = approximately 0.29 km (approximately 290 km).
m), PLOAM cells can be received from ONUs existing in the range.

In this case, for example, from 1.16 km to 1.
ON in the range up to 74 km (580 m range)
If a PLOAM cell is received only from U, an area for two cells may be secured. In addition, O existing in this range
The time for receiving a PLOAM cell from a NU is 11.6 μs at the shortest and 17.4 μs at the longest. Therefore, by securing an area for two cells as an area where the PLOAM cell returns within 17.4 μs,
Delay control can be performed on ONUs in this range.

Since the OLT 1 stores the transmission path distance to each ONU in the storage unit as position information, an area for receiving a PLOAM cell from a certain range centered on the transmission path distance is specified and secured. be able to. The position information is a transmission path distance from the OLT 1 to each ONU.
The information need not be the transmission path distance as long as the information can specify the area within the distance measurement window.

When the entire distance measurement window is opened,
An example in which only the area specified by the position information is secured and the distance measurement window is opened is shown in the figure. FIG. 2 shows a distance measurement window when the entire area of 69 cells is secured. The range indicated by the arrow in FIG. 2 is the secured area. The area to be secured becomes wider as the longest transmission path distance becomes longer. FIG. 3 is a graph centered on a transmission path distance stored as acquired position information.
An example is shown in which a reception area for receiving PLOAM cells from a range of 290 m (± 1 cell) is secured. The area corresponding to the two cells indicated by the arrows is the reserved area.

An ONU whose position information is known once in the operation state becomes non-operation state, and the OLT 1
Is started again in the operating state, the distance can be measured if the necessary area is secured. In the example shown in FIG. 3, the cells that are not opened can be effectively used as an area for receiving data cells and the like.

When the distance measuring unit 11 performs distance measurement,
The state of the distance measurement window is not always constant.
The distance measurement window illustrated in FIG. 2 and the distance measurement window illustrated in FIG. 3 may be used periodically. This control is performed by the distance measurement window width determination unit 13. The distance measurement window width determination unit 13 changes the width of the distance measurement window shown in FIG. 3, and the frequency (ratio) of generating the two types of distance measurement windows shown in FIGS. 2 and 3 is changed.

Next, the operation of the star configuration communication system at the time of initial connection will be described. The distance measuring unit 11
An uplink cell transmission request is transmitted to each ONU, and the time from the transmission to the reception of each PLOAM cell is measured. At the time of the initial connection, the distance measurement window generation instructing unit 14 secures an area of the entire distance measurement window as illustrated in FIG. By securing the entire area of the distance measurement window, PLOAM from each ONU within the longest transmission path distance range
Cells can be received. The distance measuring unit 11 calculates a time to be delayed by each ONU based on the measured time,
An instruction is given to each ONU, "Hold only the delay time before sending cells." Further, the transmission path distance to each ONU calculated from the measured time is stored in the storage unit as position information.

The condition for the successful distance measurement is that the PLOAM cell is received while the distance measurement window is open, and the deviation of the arrival fluctuation phase of the PLOAM cell is ± 2 bits.
Is within the range. When the OLT 1 transmits an upstream cell transmission request to the ONU, the phase at which the upstream cell arrives at the OLT 1 is predicted to be a specific phase based on the upstream cell transmission request. The arrival variation phase is the actual phase that deviates from this predicted phase. The success condition of the distance measurement in the present invention is not limited to “within ± 2 bits”. However, the condition “within ± 2 bits” is based on ITU's “TELECOMMUNICATION STANDARIZAT
Standard "G.983.1" by "STUDY GROUP 15" of ION SECTOR
It is desirable that this condition be a success condition of the distance measurement.

Next, a description will be given of a distance measurement operation in a case where the ONU once in the operation state and the position information is known temporarily becomes the non-operation state, and the OLT 1 restarts the ONU to put it in the operation state. The time to be delayed once is set for the ONU to be restarted. However, if the transmission path distance is changed due to replacement of an optical fiber or a change in the installation position of the ONU, the accuracy of the delay deteriorates, and it is necessary to measure the distance again. The distance measuring unit 11 issues an instruction to send back the PLOAM cell to the ONU to be restarted, and
The ONU receives the OAM cell, calculates the time to be delayed by the ONU, and notifies the ONU of the delay time. At this time, the distance measurement window generation instructing unit 14 opens the entire distance measurement window as illustrated in FIG. If the first distance measurement is successful, the distance measurement unit 11 ends the distance measurement.

However, if the ONU is turned off,
In the case of the non-operation state due to a transmission line failure or the like, the distance measurement may fail. In this case, the distance measurement unit 11 notifies the distance measurement failure counting unit 12 of information indicating that the measurement has failed, and performs the distance measurement again after a predetermined time has elapsed. This time is called a restart operation trial interval. The distance measurement unit 11 measures the distance at each restart operation trial interval until the distance measurement is successful. If the restart operation trial interval is short, the area is often occupied, and if the restart operation trial interval is long, it takes a long time to complete the distance measurement, so an optimal value is set.

The distance measurement failure counting section 12 counts the number of times the distance measurement has failed, and determines that the count value is equal to the threshold value P.
Each time it exceeds 1, P2,..., It is notified to the distance measurement window width determination unit 13.

When the count value exceeds the first threshold value P1, the distance measurement window width determination unit 13 uses the distance measurement window as shown in FIG. The setting is changed so that a distance measurement window that secures only a part of the area is used. When the distance measurement unit 11 receives a PLOAM cell used for delay control, the distance measurement unit 11 determines which of the two types of distance measurement windows to select, and determines the frequency at which each distance measurement window is selected.

The distance measurement window generation instructing unit 14 generates a distance measurement window when the distance measurement unit 11 performs distance measurement in accordance with the setting of the distance measurement window width determination unit 13. When generating a distance measurement window that secures only a part of the area as shown in FIG. 3, the distance measurement window generation instructing unit 14 determines the area to be secured based on the ONU position information.

Accordingly, the distance measurement unit 11 measures the distance by the distance measurement window as shown in FIG. 2 until the number of failures exceeds the threshold value P1, but when the number of failures exceeds P1, the distance measurement unit 11 returns to FIG. The distance measurement is also performed by the distance measurement window shown. For example, the distance measuring unit 1
1 repeatedly performs the distance measurement window shown in FIG. 2, and then performs the distance measurement window shown in FIG. 3, and then performs the distance measurement window n times.

When the number of failures in distance measurement further increases and the count value exceeds the next threshold value P2, P3,..., Each time the distance determination window width determination unit 13 It is set so that the frequency of the distance measurement window that secures only is increased.

A specific example of the above operation will be described. The longest transmission path distance is 20 km, and each ONU is 20 km from OLT1.
m. In addition, 20 at the time of initial connection
When distance measurement is performed on ONUs within a distance of km, a 9.6M area corresponding to 69 cells shown in FIG. 2 is secured, and a distance measurement window in which only a part of the area is secured is opened. Is to secure an area for two cells as shown in FIG. By securing an area corresponding to one cell, it is possible to measure the distance of an ONU existing in a range of about 290 m.
Distance measurement is possible in the range of 0 m. The restart operation trial interval when distance measurement fails is 100 ms,
The threshold is 600, 1200, 3000, 6000,
15,000, 30,000, 60000. Hereinafter, the distance measurement windows shown in FIGS. 2 and 3 are referred to as 69 cell windows and 2 cell windows, respectively.

FIG. 4 is a graph showing an example of a change in the number of times a 69-cell window is opened in 10 seconds, and the horizontal axis shows the elapse of the distance measurement continuous failure time. Restart operation trial interval is 1
00 ms, the number of failures is the first threshold 600
Is 1 minute. The distance measuring unit 11
The distance measurement is performed 600 times in one minute, and the distance measurement is performed using a 69-cell window. Therefore, 10
The number of times the 69-cell window is opened during s is 100 as shown in FIG.

Until the next threshold value 1200 is exceeded, that is, until two minutes have elapsed, the distance measurement window width determination unit 13
Is set to open the 69-cell window and the 2-cell window at the same frequency (1: 1 ratio). In the distance measurement from the 601th time to the 1200th time, each window is opened 300 times at the same frequency.
The number of times the 9-cell window is opened is 50 as shown in FIG.
Times.

Similarly, each time the number of failures exceeds each threshold, the distance measurement window width determination unit 13 reduces the frequency of the 69-cell window. Until the first threshold is exceeded, only the 69-cell window is opened. Each time the threshold is exceeded, the ratio of the 69-cell window to the 2-cell window is changed to 1/1, 1/4, 1/9, 1/24, 1 /
Change to 49, 1/99. FIG. 5 is an explanatory diagram showing a change in the generation frequency of two types of distance measurement windows. FIG.
In, the thick line indicates the 69 cell window, and the thin line indicates 2 cell window.
Shows the cell window. FIGS. 5A, 5B, and 5C show that, when the distance measurement continuous failure time is within 1 minute (the number of continuous failures is 600 times or less), from 1 minute to 2 minutes (the number of continuous failures is 601 to 1200 times). ) Indicates the frequency of the distance measurement window in the case of 5 to 10 minutes (the number of consecutive failures is 3001 to 6000). As shown in FIG. 5, the distance measurement window width determination unit 1
3 reduces the frequency of opening 69 cell windows.

The order in which the two types of distance measurement windows are generated is not limited to the case shown in FIG. For example,
In FIG. 5B, the setting may be such that the 69-cell window and the 2-cell window are opened alternately. The same applies to other cases.

FIG. 6 is a graph showing a change in the number of cells opened per 10 s. As shown in FIG. 4, if the continuous failure time of the distance measurement is within one minute, 100 cell windows are opened 100 times per 10 s, so the number of cells is 6,900. Until the elapse of 2 minutes, each window is opened 50 times per 10 seconds, so that the number of cells is 3550. In addition, it is 870 times from 5 minutes to 10 minutes. In addition, the number of times is 267 times for one 69-cell window after 100 minutes when the 2-cell window is opened 99 times.

Comparing the total number of cells opened per 10 s, the case shown in FIG. 5B is 51.4% of that shown in FIG. 5A, which is almost halved. FIG. 5 (c)
In the case of the above, it becomes 12.6%.

After 100 minutes when two cell windows are opened 99 times for one 69-cell window, this ratio decreases to about 3.87%. This is about 9
The area corresponding to 6.13% means that it can be used effectively other than for distance measurement. When an area of 9.6 M is secured as an area for 69 cells, a maximum area of about 9.2 M can be used for purposes other than distance measurement. One O
Assuming a system in which a maximum of 32 ONUs are connected to LT1 and an area of about 4.4M is assigned to each ONU, an area corresponding to two or more ONUs is effectively used after 100 minutes in FIGS. It becomes possible.

In such a star configuration communication system,
The location information is stored for the ONU once in the operating state, and in the subsequent distance measurement, a necessary reception area is secured based on the position information, so that the area occupied for the distance measurement is reduced. Effective utilization becomes possible.

When the ONU whose operation information is once known and the position information is known temporarily enters the non-operation state, and the OLT 1 activates the ONU again to enter the operation state, the distance measurement window set by the distance measurement window unit 13 is set. Is not limited to the above description, and the frequency of the narrow distance measurement window may be increased from the beginning. However, although rare, the distance between the OLT 1 and the ONU may fluctuate greatly when the ONU is put into a non-operation state due to a transmission line failure or the like. Considering such a case,
At first, it is desirable to increase the rate of opening the entire distance measurement window, and increase the frequency of the narrow distance measurement window as the number of distance measurement failures increases. Also,
When opening a narrow distance measurement window, a wider (or narrower) area may be secured instead of opening a two-cell window.

When changing the frequency of the distance measurement window, the distance measurement failure counting unit 12 does not count the number of failures, but a timer measures the time during which distance measurement failures continue. The configuration may be such that the distance measurement window width determination unit changes the frequency when the threshold value is exceeded.

Each of the above numerical values is a specific example, and the subscriber access system and the optical line terminal of the present invention are not limited by the above numerical values.

[0052]

According to the present invention, in the subscriber access system, the station-side device provides area specifying information for specifying the area for receiving the delay control cell for each of the subscriber-side apparatuses for which the delay time has been set at the time of the initial connection. This is the configuration to be created. Therefore, in the subscriber access system, when the delay time is set again in the subscriber device, the occupancy of the area for receiving the delay control cell can be reduced, and the reception area can be used effectively.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical line terminal applied to a subscriber access system according to the present invention.

FIG. 2 is an explanatory diagram showing an example of a distance measurement window in which all areas used for distance measurement are secured.

FIG. 3 is an explanatory diagram showing an example of a distance measurement window in which a part of an area used for distance measurement is secured.

FIG. 4 is a graph showing an example of a change in the number of times a 69-cell window is opened.

FIG. 5 is an explanatory diagram showing a change in generation frequency of two types of distance measurement windows.

FIG. 6 is a graph showing an example of a change in the number of cells used for distance measurement.

FIG. 7 is a block diagram illustrating an example of a configuration of a star configuration communication system.

[Explanation of symbols]

 Reference Signs List 1 station apparatus 2 subscriber apparatus 11 distance measurement unit 12 distance measurement failure count unit 13 distance measurement window width determination unit 14 distance measurement window generation instructing unit

Claims (6)

[Claims] 1. A subscriber access system in which a station apparatus and a plurality of subscriber apparatuses are connected, wherein the station apparatus comprises:
A cell transmission request instructing the transmission of a delay control cell is transmitted to each subscriber unit, and a cell transmission request is transmitted to each subscriber unit based on the time from transmitting the cell transmission request to receiving the delay control cell. In a subscriber access system provided with a delay control means for setting a delay time at the time of transmission, an optical line terminal specifies an area for specifying a reception area of a delay control cell for each subscriber side apparatus for which a delay time is set at an initial connection. A subscriber access system comprising an area specifying information creating means for creating information. 2. A plurality of subscriber units are connected to each other to constitute a subscriber access system, and transmit a cell transmission request instructing transmission of a delay control cell to each subscriber unit and transmit a cell transmission request. Station device equipped with delay control means for setting a delay time at the time of cell transmission to each subscriber device based on the time from when the delay control cell is received, and setting the delay time at the time of initial connection. A station-side apparatus applied to a subscriber access system, characterized by comprising area specifying information generating means for generating area specifying information for specifying a reception area of a delay control cell for each of the subscriber-side apparatuses. 3. The delay control means, when receiving a delay control cell for setting a delay time again for a subscriber unit having set a delay time at the time of initial connection, specifies the same reception area and area as at the time of initial connection. 3. The station-side device applied to the subscriber access system according to claim 2, wherein one of the reception areas specified by the information is selectively secured to receive the delay control cell. 4. The delay control means, when setting the delay time again for the subscriber device for which the delay time was set at the time of initial connection, if the setting of the delay time has repeatedly failed, the same reception area as at the time of the initial connection. 4. A station-side apparatus applied to a subscriber access system according to claim 3, further comprising a frequency changing means for changing the frequency when securing the reception area and when securing the reception area specified by the area specifying information. . 5. The frequency changing means, when the number of times of failure in setting the delay time exceeds a predetermined threshold value, to secure the same reception area as at the time of the initial connection, and to determine whether the reception area is specified by the area identification information. 5. The station-side device applied to the subscriber access system according to claim 4, wherein the frequency at which the area is reserved is changed. 6. The method according to claim 4, wherein the frequency changing unit increases the frequency of securing a reception area specified by the area specifying information when the setting of the delay time has repeatedly failed. An optical line terminal applied to a subscriber access system.