JP2000078177A - Subscriber terminating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide subscriber terminating device capable of avoiding the problem of delay of ATM cells. SOLUTION: Concerning the subscriber terminating device which contains plural pieces of subscriber equipment and applies the right of transmission to the specified subscriber equipment, this device is provided with plural band generating means 32 for generating first polling signal corresponding to the bands of respective pieces of subscriber equipment, an FIFO 33 for storing the first polling signals generated by the plural band generating means 32, a read control means 34 for performing reading from the FIFO 33 when inhibit signal is inactive and stopping reading from the FIFO 33 when the read inhibit signal is active, a polling signal generating means 35 for generating a second polling signal instructing a response to the specified subscriber equipment, and a polling control means 36 for making the read inhibit signal active and instructing the generation of the second polling signal to the polling signal generating means 35 when the number of first polling signal stored in the FIFO 33 gets not more than a fixed number.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a subscriber termination device, and more particularly to window control.

[0002]

2. Description of the Related Art An ATM (Asynchronous Transfer Mobility) that divides various multimedia services (voice, video, data) into fixed-length cells and enables integrated processing.
de: Asynchronous transfer mode) technology and PO that reduces the price of the system by sharing optical transmission equipment among multiple users
N (Passive Optical Network)
An ATM-PON is an access communication system that makes use of both features of the technology.

FIG. 7 is a diagram showing a network configuration of an ATM-PON. As shown in this figure, a subscriber terminating device (hereinafter, OLT) 2 installed in a telephone station and a plurality of subscriber devices (hereinafter, ONU (Optic) installed in a building or a home.
al NetworkUnit)) 4 # 1 to 4 # x are connected through an optical fiber by a splitter called a star coupler 6 which is a passive element.

[0004] Information is accommodated in ATM cells and is transferred in units of cells to which additional bytes necessary for communication on the PON of the optical transmission line are added. OLT2 to ONU4 # 1 ~ 4 # x
Is transmitted by a continuous signal of ATM cells, and each ONU performs communication by receiving information addressed to itself.

On the other hand, OLT2 from ONUs 4 # 1-4 # x
As for the upstream signal, the OLT 2 transfers a polling signal for granting a transmission right to a specific downstream ONU, performs polling, and performs one ONU 4 # i in one time slot.
The ONU 4 # i sets an ATM cell in the assigned time slot and transfers information.

In the ATM-PON, polling is
PLO at a specific position in a frame (eg, 56 cells)
A cell dedicated to polling called an AM cell is prepared, and an identifier (for example, an ONU serial number) of the ONU 4 # i that gives a transmission right to the PLOAM cell is set.
U4 # j (j = 1 to x) and ONU4 that gives transmission right to the area preceding the header of each ATM cell.
This is performed by a method of setting and transferring the #U ONU serial number and the like.

Then, OLT2 → ONU4 # i → OLT
2 round trip delay to all ONU4 # i
(I = 1 to x) is fixed so that communication is performed while avoiding collision between upstream ATM cells.

FIG. 8 is a diagram showing a round trip delay of the ATM-PON. However, under normal conditions,
As shown in FIG. 8, the round trip delay Di differs depending on the distance from the OLT 2 to each ONU 4 # i and the processing in each ONU 4 # i. Therefore, the land trip delay D _max of the furthest ONU is closer to the closest ONU 4 # i.
By giving the delay Xi (= _Dmax- Di) electrically in order to provide the same land trip delay, the delay of all subscribers can be made the same.

[0009] Therefore, in the ATM-PON system,
It is necessary to measure the round trip delay Xi from the OLT 2 to each ONU 4 # i before starting communication, and to electrically delay each ONU 4 # i so as to be the same as the maximum allowable delay _Dmax . This delay measurement is performed each time a new ONU is connected to the OLT.

FIG. 9 is a configuration diagram of a conventional OLT. FIG. 10 is a configuration diagram of the ONU in FIG. FIG. 11 is a diagram showing conventional window control.

FIG. 12 is a diagram showing a conventional window opening timing. ONU band generator 8 # i (i = 1
To x) correspond to ONU4 # i according to the band of ONU4 # i.
Generates a polling signal for giving the right to transmit an upstream ATM cell. The MUX 10 multiplexes the polling signal generated by the ONU band generation unit 8 # i, and performs FIFO (First In)
First Out) 12. The read control unit 14
The polling signal written in O12 is read.

To measure the delay of the ONU 4 # n, the window control unit 16 sends the read control unit 14 a FIFO 14
To activate the read stop signal. Read control unit 14
When the read stop signal becomes active,
Stop reading from.

The window control unit 16 includes a read control unit 14
After a read stop signal is activated for a certain period of time, the polling signal generator 18 for delay measurement is instructed to generate a polling signal.

[0014] The certain time period means that cells transmitted by a plurality of ONUs 4 # i that have obtained a transmission right by a polling signal included in the time period are transmitted by ONUs with no delay in response cells to polling signals for delay measurement and the like. The time that does not reach from D _min to D _max with reference to the time that has been performed.

The delay measurement polling signal generator 18 includes:
A polling signal for delay measurement of the ONU 4 # n is generated. This polling signal is transferred from OLT 2 to ONU 4 #n. When the receiving unit 24 receives a polling signal for delay measurement via the WDM coupler 22, the ONU 4 #n generates an ATM cell for delay measurement response in the control unit 26, and transmits the WDM coupler 22 from the transmitting unit 28. Via O
Transfer to LT2.

The OLT 2 calculates a delay time Dn from the arrival time when the ONU with no delay responds to the arrival of the delay measurement response ATM cell, and calculates (D _max -Dn) as the delay to be inserted by the ONU 4 #n. Is set as a downstream ATM cell, and the ONU 4 # n is notified.

As shown in FIG. 11, while measuring the delay time of the ONU 4 # n, the upstream A
The transfer of TM cells must be stopped. The stop time is, for example, the distance from the OLT 2 to the ONU is 0 to 2
Assuming 0 km, a delay variation of (D _max −D _min ) = about 200 μs is considered, during which time (for example, 155.52 M
In the case of bps, 73 cells), the transfer of the upstream ATM cell is stopped.

Therefore, the distance to ONU2 # n is 0 to 2
If the distance is only known as a distance between 0 km, as shown in FIG. 11, a delay measurement area (window) is opened during uplink communication of another ONU, and delay measurement is performed. After measuring two to five times to check the accuracy of the delay measurement, etc.,
The difference from the maximum distance delay time is electrically delayed to start communication.

[0019]

However, conventionally,
If delay measurement is necessary, a polling signal for delay measurement is transferred, and communication of other ONUs is stopped while the window is opened. The cells during that time are accumulated in the transmission waiting buffer 30 in the ONU, and the delay increases. Furthermore,
If the operation is performed continuously two to five times, the delay is further accumulated, and the possibility that the delay increases is large. Moreover, as shown in FIG. 12, this window was opened periodically.

ATM has a service class such as a CBR service having a limited delay time, such as a telephone, and a UBR service, such as a data communication, which allows a certain delay, such as data communication. Therefore, if the delay measurement window is continuously opened two to five times, a cell from the ONU to the OLT is delayed, and there is a problem that a delay variation of a service whose delay time is limited such as a CBR service becomes large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and provides a subscriber terminating device which can control the influence of a window so as not to remain in the next window, thereby avoiding the problem of delay of ATM cells. It is intended to provide.

[0022]

FIG. 1 is a diagram illustrating the principle of the present invention. As shown in this figure, according to the present invention, a plurality of subscriber devices (for example, ONUs, hereinafter referred to as ONUs) 31 # i (i = 1 to x) are accommodated, and a specific ONU 3
In the subscriber terminating device 22 that gives the transmission right to 1 # j,
A plurality of band generating means 32 # i (i = 1 to x) for generating a first polling signal for giving a transmission right to each ONU 31 # i in accordance with the band of each ONU 31 # i;
FIF for storing the first polling signal in which 2 # i has occurred
When O33 and the read inhibit signal are inactive,
The first polling signal is read from O33, and when the read inhibit signal is active, the read control means 34 for stopping reading of the first polling signal from the FIFO 33, and the polling signal generating means 35 for generating the second polling signal.
After the polling signal generating means 35 generates the second polling signal, if the number of the first polling signals stored in the FIFO 33 becomes equal to or less than a certain number, the read inhibition signal is activated and the polling signal generating means 35 2 Polling control means 36 for instructing generation of a polling signal
And a subscriber terminating device provided with the following.

According to the above configuration, the plurality of band generating means 32 # i (i = 1 to x) provide the ONU 31 # i with a transmission right in accordance with the band of each ONU 31 # i. Generate a signal. This first polling signal is F
The data is sequentially stored in the IFO 33. Polling control means 36
If the number of the first polling signals is less than a certain number in the FIFO 33 after the polling signal generating means 35 generates the second polling signal for delay measurement or the like, the second polling signal is generated last time. ONU31 # i
It is determined that the influence of the delay of the transmission from is suppressed.

Then, the polling control means 36 activates the read inhibit signal and activates the polling signal generation means 3.
5 is instructed to generate a second polling signal. Thereby, the ONU by generating the second polling signal
Delay fluctuation of the transmission signal from 31 # i can be suppressed.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 2 is a configuration diagram of an OLT according to a first embodiment of the present invention.

As shown in FIG. 1, the OLT includes an interface unit 42, a band setting unit 44, and an ONU band generation unit 46.
#I (i = 1 to x), MUX 48, FIFO 50, read control unit 52, window request unit 54, window control unit 56, empty flag 58, window prohibition flag 6
0, delay measurement polling signal generator 62, selector 6
4, a PLOAM cell generator 66, a FIFO 68, a frame generator 70, and a selector 72.

The interface unit 42 receives the band of each ONU 82 #i (i = 1 to x) specified by the control system 40 and outputs the band to the band setting unit 44. It controls the interface between the two. The control system 40 notifies the OLT interface unit 42 of the bandwidth of each ONU 82 # i.

The timing at which the bandwidth is notified to the interface unit 42 is determined when each ONU 82 # i joins or when the ONU
82 #i. When the band is notified when the ONU 82 # i subscribes, for example, the ONU
In this case, the band of 82 # i is used by a PVC (Permanent Virtual Call), and the control system 40 is a switching center device or the like. The case where the ONU 82 # i is notified of the band at the time of outgoing / incoming calls is, for example, SVC (Signaling Virtual
Call) (for example, telephone service), and the control system 40 is an exchange.

The band setting unit 44 includes an interface unit 42
It receives the band information of the ONU 82 # i and sets the band in the ONU band generating section 46 # i. The ONU band generation unit 46 # i synchronizes with the clock CLK and, in accordance with the band of the ONU 82 # i set by the band setting unit 44, generates a polling signal (for example, if the band is 1 Mbps, the ONU 82 # i And grants a transmission right so that the ATM cell can be transferred at the transmission rate).
X48.

The MUX 48 includes an ONU band generator 46 #
The polling signal output from i is stored in a buffer, multiplexed, and written to the FIFO 50. FIFO 50 is a FIFO that stores a polling signal.
O memory.

The read controller 52 stops reading the polling signal from the FIFO 50 when the read inhibit signal is active, and reads the polling signal from the FIFO 50 at a constant speed when the read inhibit signal is inactive. Output. The read control unit 52
When the FIFO 50 becomes empty, the empty flag 58 is turned on ("1"), and when the polling signal is stored in the FIFO 50, the empty flag 58 is turned off.

The window request unit 54 requests the window control unit 56 to open a window. The window request is automatically searched for the ONU serial number of an unspecified ONU newly connected to the OLT,
In order to assign an ON-ID, a new connection is made and the PON-
This is the case where the delay measurement of the ONU 82 # n to which the ID is given is performed again, and when the OLT is restarted, the delay measurement of the ONU 82 # i is performed again. For these reasons, requests for windows are made at regular intervals. Below,
A case for delay measurement will be described as an example. Window control unit 5
6 has the following functions.

When the window request signal becomes active, when the window prohibition flag 60 is off, the window prohibition flag 60 is turned on (“1”), the read prohibition signal is activated for a certain period of time, and then the generation instruction signal is activated. I do. After that, the read inhibition signal is made inactive.

When the window request signal becomes active, when the window prohibition flag 60 is on, a wait is performed until the window prohibition flag 60 is turned off.
The window prohibition flag 60 is turned on, the read prohibition signal is activated for a certain period of time, and then the generation instruction signal is activated. After that, the read inhibition prohibition signal is made inactive.

When the wind prohibition flag 60 is on,
When the empty flag 58 is turned on, the window prohibition flag 60 is turned off. Whether or not the empty flag 58 is turned on may be periodically monitored by an interval timer or the like, and an interrupt signal may be sent to the window control unit 56 when the empty flag 58 is turned on. .

The selector 64 outputs a selection signal for selecting any one of the output of the FIFO 50 and the polling signal for delay measurement. Empty flag 58
Is a flag that is turned on by the read control unit 52 when the FIFO 50 is empty. The window prohibition flag 60 is turned on when prohibiting opening of a window.

Here, the window prohibition flag 60 is turned on when a polling signal for opening a window is transferred, and turned off when the polling signal for opening a window is activated when the OLT is started. This is when the empty flag 58 is turned on after the transfer.

As described above, in the next window, since the FIFO 50 is empty after the previous window is opened (the bandwidth of all ONUs 82 #i is secured), another window is opened. The delay fluctuation of ONU cell transmission can be suppressed.

In the present embodiment, the next window is opened when the FIFO 50 becomes empty. However, when the polling signal of the FIFO 50 becomes less than a certain number, the next window is opened. You may do it.

The polling signal generator for delay measurement 62
When the generation request signal becomes active, a polling signal for delay measurement is generated. The selector 64 selects the output of the FIFO 50 or the polling signal for delay measurement according to the selection signal. The PLOAM cell generator 66 generates a PLOAM cell from the polling signal output from the selector 64. Here, the case where the polling signal is transferred by the PLOAM cell is described. However, the case where the polling signal is transferred in another format may of course be used.

The FIFO 68 is a FIFO memory for storing a main signal (down cell). Read control unit 67
Is for reading out a downstream main signal from the FIFO 68 at a constant speed. The frame generator 70 receives the clock CLK
In synchronization with the above, a selection signal for selecting a PLOAM cell and a main signal cell is generated in accordance with a prescribed frame format. The selector 72 selects a PLOAM cell or a main signal according to a selection signal.

FIG. 3 is a time chart of FIG. Hereinafter, the operation of FIG. 2 will be described. (A) Bandwidth generation The bandwidth of each ONU 82 #i (i = 1 to x) is applied at the time of contract, and is notified from the control system 40 to the bandwidth setting unit 44 via the interface unit 42. Alternatively, each ONU
82 #i (i = 1 to x) to the control system 40
To the band setting unit 44 via the interface unit 42.

The band setting section 44 includes an interface section 42
Then, the bandwidth of each ONU 82 # i (i = 1 to x) is input and set in the ONU bandwidth generation unit 46 # i. The ONU band generator 46 # i synchronizes with the clock CLK so that the ONU 82 generates a bit rate equal to the set band.
#I, an upstream polling signal (for example, ONU8
2 # i) and outputs it to the MUX 48.

The MUX 48 is an ONU band generator 46 # i
Is input to the buffer, multiplexed, and written to the FIFO 50. Read control unit 5
2 if the read inhibit signal is inactive, the FIFO
The polling signal is read out from the register 50 and output to the selector 64.
The reading of the polling signal is stopped from 0. Also, F
If the IFO 50 is empty, the empty flag 58
Is turned on, and if not empty, the empty flag 58 is turned off.

(B) Window Request The window request unit 54 is a newly connected unspecified ON.
The ONU serial number of U82 # n is obtained and the PON-
As shown in FIG. 3, the window request signal is activated periodically to measure the delay time of the ONU 82 # n to which the PON-ID has been assigned in order to automatically assign the ID.

(C) Window Control FIGS. 4 and 5 are flowcharts of the window control unit in FIG. In step S2 in FIG. 4, it is checked whether there is a window request from the window request unit 54. If there is a window request, the process proceeds to step S4.
If there is no window request, the process waits in step S2.

In step S4, it is checked whether the window prohibition flag 60 is on. If the window prohibition flag 60 is on, a wait is made in step S4.
If the window prohibition flag 60 is off, step S6
Proceed to.

For example, at times Ta and Tc at which a window request is made in FIG. 3, the window prohibition flag 60 is off, so that the process proceeds to step S6. Waiting is performed until the flag 60 is turned off.

In step S6, the window prohibition flag 60 is turned on. In step S8, the read prohibition signal is activated as shown in FIG. In step S10, it is checked whether a certain time has elapsed. If the certain time has not elapsed, the process waits until the certain time has elapsed, and if the certain time has elapsed, the process proceeds to step S12. When the read prohibition signal becomes active, the read control unit 52 stops reading the polling signal from the FIFO 50.

In step S12, the generation request signal is activated. Polling signal generator 6 for delay measurement
2 generates a delay measurement polling signal and outputs it to the selector 64 when the generation request signal becomes active.

In step S14, the read inhibit signal is made inactive. When the read inhibition signal becomes inactive, the read control unit 52 sets the FIFO5 at a constant speed.
The polling signal is read from 0.

The window control section 56 outputs a polling signal for delay measurement when the read inhibit signal is active, and outputs a FIFO5 signal when the read inhibit signal is inactive.
The selection signal is output to the selector 64 so as to select the output of 0.

The selector 64 sets the FI in accordance with the selection signal.
The output of the FO 50 or the polling signal for delay measurement is selected and output to the PLOAM cell generator 66. PLOAM
The cell generator 66 outputs the PLOAM
A cell is generated and output to the selector 72.

On the other hand, in step S20 in FIG.
8 is monitored, and if the empty flag 58 is on, the window prohibition flag 60 is turned off. If the empty flag 58 is off, the process ends.

As a result, once the window is opened, the next window is not opened until the empty flag 58 is turned on. Therefore, at the time of opening the next window, the cell delay caused by opening the previous window is set. Fluctuations have been reduced.

(D) Transfer of ATM cells ATM cells, which are main signals, are stored in the FIFO 68. The read control unit 67 reads out the down cell from the FIFO 68 at a constant speed, and outputs it to the selector 72. The frame generating unit 70 outputs the output of the FIFO 68 or a selection signal for selecting a PLOAM cell according to a specified frame format.

The selector 72 sets the FI in accordance with the selection signal.
Select output of FO68 or PLOAM cell. The cell selected by the selector 72 is converted into an optical signal by an electric / optical converter (not shown), and
82 # i (i = 1 to x).

(E) Transmission of Cell Upon receiving a polling signal that matches its own PON-ID, the ONU 82 # n generates a delay measurement cell,
For example, after a lapse of the time defined by the time slot number from the upstream first frame, the frame is transferred to the OLT.

The OLT is an ONU when the delay time is zero.
The delay time Dn from the time when the delay measurement cell is received from the time to the time when the delay measurement cell is actually received is measured. The measurement of the delay time Dn is repeated several times, an average value is calculated, and ( _Dmax- Dn) is notified to the ONU 82 # n. At the time of communication, the ONU 82 # n sets (D _max
−Dn), and output an upstream cell with an electrical delay.

According to the first embodiment described above, once a window is opened, the next window is not opened until the empty flag 58 is turned on.
Delay variation of M cells can be suppressed.

Second Embodiment FIG. 6 is a block diagram of an OLT according to a second embodiment of the present invention, wherein substantially the same elements as those in FIG. 2 are denoted by the same reference numerals.

The difference between the OLT according to the second embodiment and the OLT according to the first embodiment is that, for a band of a CBR service class whose delay time is limited (hereinafter, a CBR band), a delay caused by opening a window is provided. For a band of the UBR service class (hereinafter, referred to as UBR band) in which fluctuation is suppressed and a certain delay is allowed such as data communication, etc., when there is a margin in the band, that is, a polling signal and delay measurement for the CBR band A polling signal for the UBR band is generated when a polling signal for the UBR band is not transferred.

In the first embodiment, the polling signal of the band combining the CRR band and the UBR band is transmitted by one FIFO.
50, the overall bandwidth of these is large,
This is because, when the available bandwidth is small, the polling signal is accumulated in the FIFO 50, and the FIFO 50 is unlikely to be empty, and the transfer of the delay measurement polling signal or the like may be delayed.

As shown in this figure, the OLT includes an interface unit 42, a band setting unit 44, an ONUCBR band generation unit 90 # i (i = 1 to x), a MUX 48, and a FIFO 5
0, read control unit 93, window request unit 54, window control unit 56, empty flag 58, window inhibit flag 60, delay measurement polling signal generation unit 62, selector 64, PLOAM cell generation unit 66, read control unit 6
7, FIFO 68, frame generator 70, selector 7
2. ONUUBR band generation section 92 # i (i = 1 to x),
It includes a MUX 94, a FIFO 96, a read control unit 98, and a selector 100.

The interface unit 42, the band setting unit 44,
MUX 48, FIFO 50, window request unit 54, window control unit 56, empty flag 58, window prohibition flag 60, polling signal generation unit 6 for delay measurement
2, the selector 64, the PLOAM cell generator 66, the read controller 67, the FIFO 68, the frame generator 70, and the selector 72 are substantially the same as those in FIG.

ONUCBR band generating section 90 # i (i = 1
To x) generate a polling signal in accordance with the CRR band of the ONU 82 # i. The ONUUBR band generation unit 92 # i (i = 1 to x) outputs the UR of the ONU 82 # i.
A polling signal is generated according to the R band.

The read control unit 93 corresponds to the read control unit 5 shown in FIG.
In addition to the functions similar to those of the second embodiment, when the read inhibit signal is inactive and the FIFO 50 is empty, the read controller 9
8, when the read permission signal is active, the output of the FIFO 96 is selected, and when the read permission signal is inactive, the selection signal is output to the selector 100 so as to select the output of the FIFO 50. Having.

The MUX 94 is connected to the ONU 82 #i (i = 1 to
The polling signal of the UBR band of x) is input to the buffer, multiplexed, and written to the FIFO 96. When the read permission signal is active, the read control unit 98 controls the FIFO at a constant speed in synchronization with the clock CLK.
96, the UBR band polling signal is read out, and the FI
When the free space of the FO 96 becomes equal to or less than a certain value and there is a possibility of overflow, the ONUUBR band 92 # i (i = 1 to 1)
x) reducing the band or temporarily prohibiting the generation of the band. The selector 100 selects the outputs of the FIFOs 50 and 96 according to the selection signal.

The operation of FIG. 6 will be described below. (A) Band setting The band of each ONU 82 # i (i = 1 to x) is set to C at the time of contract.
Apply for BR band, UBR band and service class,
The control system 40 notifies the bandwidth setting unit 44 via the interface unit 42 for each service class. Or,
By the SVC to each ONU 82 #i (i = 1 to x), the control system 40 notifies the band setting unit 44 via the interface unit 42 for each service class.

The band setting section 44 includes an interface section 42
Then, the bandwidth for each service class of each ONU 82 #i (i = 1 to x) is input, the CBR band is set in the ONUCBR band generation unit 90 #i, and the UBR band is set in the ONUUBR band generation unit 92 #i. .

(B) CBR Band Generation ONUCBR band generation section 90 # i generates an upstream polling signal (eg, serial number of ONU 82 # i) for ONU 82 # i so as to have a bit rate equal to the CBR band. And outputs it to the MUX 48. In addition, CB
Information indicating that the service class is CBR may be added to the polling signal of the R band. MUX
48, a polling signal from the ONUCBR band generating section 90 # i is input to a buffer, multiplexed, and
Write to FO50.

If the read inhibit signal is inactive, the read control unit 93 reads the polling signal from the FIFO 50 at a constant speed and outputs it to the selector 100. If the read inhibit signal is active, the read control unit 93 reads the polling signal from the FIFO 50. Stop. Further, the reading control unit 93
Makes the read control unit 98 activate the read permission signal when the read inhibit signal is inactive and the FIFO 50 is empty, and otherwise deactivates the read permission signal.

(C) UBR Band Generation ONU UBR band generation section 92 # i generates an upstream polling signal (eg, serial number of ONU 82 # i) for ONU 82 # i so as to have a bit rate equal to the UBR band. And outputs it to the MUX 94. UB
Information indicating that the service class is UBR may be added to the polling signal of the R band. MUX
94 inputs a polling signal from the ONUUBR band generation unit 92 # i to a buffer, multiplexes the polling signal, and
Write to FO96.

The read control unit 98 reads the UBR band polling signal from the FIFO 96 at a constant speed if the read permission signal is active, and stops reading from the FIFO 96 if the read permission signal is inactive.

The read enable signal becomes active, and the UBR
The band polling signal is output when there is no polling signal in the CBR band and the window is not opened, and there may be a case where the delay fluctuation of the cell in the UBR band occurs. There is no problem because it is greatly allowed.

When the free space of the FIFO 96 becomes equal to or smaller than the lower limit, the read control unit 98 sets the ONUUBR band generation unit 92
#I temporarily reduce the UBR band or ONU
The UBR band generation unit 92 # i is instructed to temporarily stop the generation of the UBR band. As a result, the occurrence of the UBR band is suppressed by opening the window,
Even if the UBR polling signal continues to accumulate in the FIFO 96, the FIFO 96 does not overflow.

The selector 100 operates according to the selection signal to output F
The outputs of the IFOs 50 and 96 are selected and output to the selector 64. (D) Window Request The window request unit 54 is a newly connected unspecified ON.
The ONU serial number of U82 # n is obtained and the PON-
In order to automatically assign an ID, a window request is periodically sent to the window control unit 56 to measure the delay time of the ONU 82 # n to which the PON-ID has been assigned.

(E) Window Control The window control unit 54 operates in the same manner as in the first embodiment, and when the window prohibition flag 60 is off, activates the read prohibition signal for a certain period of time, and then controls the delay measurement. The generation of the polling signal is instructed to the delay measurement polling signal generator 62. As a result, for the CBR band, the cell delay fluctuation due to the opening of the window can be minimized, and the delay fluctuation for opening the delay measurement window can be minimized.

(F) Transfer of ATM Cell The ATM cell, which is the main signal, passes through the coupler 80 and the ONU 82 #i (i = 1 to 1) in the same manner as in the first embodiment.
x).

(G) Cell Transmission Upon receiving a polling signal that matches its own PON-ID, the ONU 82 # n generates a delay measurement cell,
For example, after a lapse of time specified by the time slot number from the head frame of the downlink, the frame is transferred to the OLT.

The OLT is an ONU when the delay time is zero.
The delay time Dn from the time when the delay measurement cell is received from the time to the time when the delay measurement cell is actually received is measured. The delay time Dn from the transfer of the polling signal to the reception of the delay measurement cell is measured.

The measurement of the delay time Dn is repeated several times.
To calculate the average, and (D_max−Dn) to ONU82
#N. At the time of communication, ONU 82 # n
(D _max−Dn) with an electrical delay, and
Is output.

Also, the polling signal causes an upstream ATM
The ONU 82 # i that has obtained the transmission right of the cell gives priority to the cell of the CBR band, for example, according to the priority of the cell transmission,
Send the cell. When a service class is set in the polling signal, a cell matching the set service class may be transmitted.

According to the second embodiment described above, the AT
We can perform polling corresponding to each service of M,
It is possible to minimize the delay variation that opens the delay measurement window.

[0085]

As described above, according to the present invention,
After the second polling signal is generated, the second polling signal is generated when the number of the first polling signals stored in the FIFO becomes equal to or less than a certain number. Transmission delay fluctuation can be suppressed.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a configuration diagram of an OLT according to the first embodiment of the present invention.

FIG. 3 is a time chart of FIG. 2;

FIG. 4 is a flowchart of a window control unit in FIG. 2;

FIG. 5 is a flowchart of a window control unit in FIG. 2;

FIG. 6 is a configuration diagram of an OLT according to a second embodiment of the present invention.

FIG. 7 is a network configuration diagram of an ATM-PON.

FIG. 8 is a diagram showing a round trip delay.

FIG. 9 is a configuration diagram of a conventional OLT.

FIG. 10 is a configuration diagram of an ONU in FIG. 7;

FIG. 11 is a diagram showing conventional window control.

FIG. 12 is a diagram showing a conventional timing for opening a window.

[Explanation of symbols]

 31 # i (i = 1 to x) ONU 32 # i (i = 1 to x) Band generator 33 FIFO 34 Read controller 35 Polling signal generator 36 Polling controller

Claims (7)

[Claims] 1. A subscriber terminating device which accommodates a plurality of subscriber devices and gives a transmission right to a specific one of the subscriber devices, wherein a transmission right is given to the subscriber device in accordance with a band of each of the subscriber devices. A plurality of band generating means for generating a first polling signal to be given; a FIFO for storing the first polling signal generated by the plurality of band generating means; and a first signal from the FIFO when the read inhibit signal is inactive. Reading a polling signal, when the read inhibit signal is active, generating read control means for stopping reading of the first polling signal from the FIFO; and generating a second polling signal for instructing a response to the specific subscriber device. Polling signal generating means, and after the polling signal generating means generates the second polling signal, the first stored in the FIFO. Polling control means for activating the read inhibit signal when the number of polling signals becomes less than a certain number and instructing the polling signal generation means to generate the second polling signal. Terminal equipment. 2. A subscriber terminating device accommodating a plurality of subscriber devices and giving a transmission right to a specific one of the subscriber devices, comprising: A plurality of first band generating means for generating a first polling signal for giving a transmission right to the subscriber device of a first service class; a first FIFO for storing the first polling signal generated by the first band generating means; When the read inhibit signal is inactive, the first FIFO
A first read control means for stopping reading of the polling signal from the first FIFO when a read inhibit signal is active; and a second polling signal for instructing a specific subscriber unit to respond. Generating polling signal generating means, and after the polling signal generating means generates the second polling signal, the first polling signal stored in the first FIFO.
When the number of polling signals becomes equal to or less than a certain number, polling control means for activating the read prohibition signal and instructing the polling signal generation means to generate the second polling signal; and a second service of each of the subscriber units. A plurality of second band generating means for generating a third polling signal for giving a transmission right to the subscriber device of the second service class in accordance with a second band of the class; A second FIFO for storing the third polling signal obtained by the first FIFO;
A second reading means for reading the second polling signal from the second FIFO when O is empty. 3. The method according to claim 2, wherein the second reading means includes a second FIFO.
3. The subscriber terminating device according to claim 2, wherein when the free space of the third band becomes equal to or less than a predetermined value, the plurality of second band generating means are instructed to suppress or stop the occurrence of the third polling. 4. The first FIFO according to a selection signal.
And a selection unit for selecting an output of the second FIFO, wherein the first reading unit outputs the selection signal.
Subscriber termination device as described. 5. The system according to claim 1, further comprising request means for periodically requesting the generation of the second polling signal, wherein the polling control means transmits the second polling signal to the polling signal generation means based on a request from the request means. 3. The subscriber terminating device according to claim 1, which indicates generation of a signal. 6. A first flag, a second flag, and if the first polling signal is not present in the FIFO, the first flag is turned on. If the first polling signal is present in the FIFO, the first flag is turned on. First flag setting means for turning off a first flag; and a second flag for turning on the second flag when the second polling signal is generated and turning off the second flag when the first flag is on. 2. The subscriber termination device according to claim 1, further comprising setting means, wherein said polling control means instructs said polling signal generation means to generate said second polling signal when said second flag is off. 7. A first flag, a second flag, and if the first FIFO does not have the first polling signal, the first flag is turned on and if the first FIFO has the first polling signal. A first flag setting unit for turning off the first flag, a second flag for turning on the second flag when the second polling signal is generated, and turning off the second flag when the first flag is on. 3. The subscriber termination device according to claim 2, further comprising: a second flag setting unit, wherein the polling control unit instructs the polling signal generation unit to generate the second polling signal when the second flag is off. .