JP5487003B2 - Optical terminal device, optical communication system, and dynamic bandwidth allocation method - Google Patents

Description

  The present invention relates to an optical terminal device, an optical communication system, and a dynamic band allocation method that dynamically allocate uplink communication time (bandwidth) in a passive optical communication network.

  In recent years, with the development of the Internet, the number of users of FTTH (Fiber To The Home) service is increasing. A PON (Passive Optical Network) is an OLT (Optical Line Terminal) installed in a communication carrier station, and an ONU (Optical Network Unit) installed in a user's home. Is a form of FTTH. The PON is an optical network in which an OLT and a plurality of ONUs are connected via an optical transmission line such as an optical fiber or a passive optical splitter, and is widely used due to its economic superiority.

  Among EPON (Ethernet (registered trademark) PON) in which OLT and ONU communicate using Ethernet (registered trademark) frames, GE-PON (Gigabit Ethernet (registered trademark) PON) having a transmission rate of 1 Gbps is high-speed, Since an inexpensive FTTH service can be provided, it is widely used especially in Japan. Recently, a standard specification of 10G-EPON having a transmission rate increased to 10 Gbps has been studied. In the standard specification of 10G-EPON, as shown in FIG. 1, it is considered that ONUs having different transmission rates of 10 Gbps and 1 Gbps are mixedly connected to the OLT.

  In general, in PON, the direction of communication from the OLT to the ONU is referred to as the downstream direction, and the opposite direction is referred to as the upstream direction. In many PONs including GE-PON, uplink communication is performed by time division multiple access. By controlling the transmission timing of each ONU by the OLT, a plurality of ONUs can perform time division communication with the OLT.

  Similarly, 10G-EPON uplink communication is performed by time division multiple access. In 10G-EPON, a method in which a plurality of ONUs having different uplink transmission rates can be connected to one OLT is being studied. At this time, uplink communication is realized by time division multiple access even between ONUs of different speeds.

  In many PONs in which upstream communication is performed by time division multiple access, in order to use the upstream bandwidth efficiently, the length of time for which upstream communication is permitted for each ONU depends on the communication status. Dynamic bandwidth allocation by changing dynamically is important. Here, the bandwidth is allocated by calculating a transmission permission amount for each ONU and exclusively securing the transmission time zone.

  GE-PON defines a protocol called MPCP (Multi Point-Control Protocol) for controlling the transmission timing of a plurality of ONUs. The OLT performs dynamic bandwidth allocation using MPCP.

  The ONU describes the amount of uplink data waiting to be transmitted as a transmission waiting amount in the transmission request signal and transmits it to the OLT. The OLT receives the transmission request signal, refers to the transmission request amount, calculates the amount of transmission permitted for each ONU and the transmission start time, writes these in the transmission permission signal, and transmits them to each ONU. At that time, control is performed so that the transmission signals of the respective ONUs do not overlap in time. The ONU starts transmission from the designated transmission start time according to the received transmission permission signal, and transmits the signal accumulated in the uplink buffer for the designated transmission permission amount.

  The method of dynamic bandwidth allocation is important in determining the performance of the PON system. The performance of the PON system can be evaluated using bandwidth utilization efficiency, delay time, and the like as indexes. In dynamic bandwidth allocation, it is important to transmit data with low delay while maintaining high bandwidth utilization efficiency. Here, the magnitude of the delay time of the actual uplink allocation band is greatly affected by the dynamic band allocation method.

  In the PON system, it can be said that the one with a shorter delay time of uplink data transmission has higher performance.

  As a method of dynamic bandwidth allocation, the OLT gives the ONU a request amount threshold that is a threshold of the transmission request amount, and causes the ONU to report the buffer accumulation amount below the threshold as the transmission request amount, and the OLT is reported from the ONU. There is a method of notifying a transmission permission amount that is matched with a transmission request amount equal to or less than the threshold value.

  Patent Document 1 discloses a method in which each ONU notifies the OLT of a transmission request amount, and the OLT permits transmission of an amount that matches the notified transmission request amount, thereby eliminating redundant bandwidth and improving bandwidth utilization efficiency. It is disclosed. At this time, a state in which a bandwidth is exclusively allocated to an ONU having a large traffic volume compared to other ONUs is prevented, and further, an upper limit value is set for the transmission request amount of each ONU in order to realize SLA (Service Level Agreement). Is supposed to be set. The allocated bandwidth can be controlled by setting the upper limit value.

JP-T-2004-528740

  However, the conventional method described above has the following two problems. Problem 1 is that band allocation cannot be performed when the round trip time (RTT) is larger than the allocation period, so if the RTT is greater than the allocation period, the allocation period needs to be greater than the RTT. As a result, when the RTT is large, the delay time is long. Further, as a problem 2, since the allocation is performed with an allocation period equal to or more than the RTT of the ONU having the maximum RTT among the connected ONUs, there is a point that the delay time of the ONU having a small RTT becomes long.

  In Patent Document 1, for the purpose of eliminating the surplus bandwidth and improving the bandwidth utilization efficiency, the OLT permits the transmission of an amount that matches the notified transmission request amount to all ONUs. In addition, when an ONU having a large RTT is connected, the delay time becomes long. Moreover, since the allocation period is determined in accordance with the ONU having the maximum RTT as in Problem 2, the delay time of the ONU having a small RTT is also increased.

  Accordingly, the present invention provides an OLT, an optical communication system, and a dynamic band allocation method capable of shortening a delay time while maintaining high band utilization efficiency when dynamically assigning an upstream band of a PON. Objective.

  In order to achieve the above object, according to the present invention, for ONUs under the OLT, an ONU that can exchange a gate and a report within a predetermined allocation period is a short-distance ONU, and an impossible ONU is a long-distance ONU. First, for the bandwidth allocation for the upstream signal from the long-distance ONU to the OLT, the estimated bandwidth based on the change in the transmission request amount from the long-distance ONU to the OLT or the actual transmission amount is allocated, and the upstream from the short-distance ONU to the OLT Signals are allocated from the remaining bandwidth in accordance with the transmission request amount from the ONU.

  Specifically, the OLT according to the present invention is connected to a plurality of ONUs through an optical transmission line, receives a report including a transmission request amount of an uplink signal requested by the ONU from the ONU, and transmits an uplink to the ONU. A transmission / reception unit that transmits a gate including a signal transmission permission amount and a transmission timing to the ONU, and an allocation period of a predetermined time are determined in advance, and the length of the optical transmission line is longer than a predetermined distance in the ONU The uplink transmission permission amount for a certain ONU is determined for each allocation cycle, and the uplink transmission permission amount of one allocation cycle for an ONU in which the length of the optical transmission line is close to less than a predetermined distance among the ONUs. The ONUs that are close to the band obtained by subtracting the uplink transmission permission amount for the ONUs in the distant destinations that are scheduled to be received in the one allocation period and are permitted to be transmitted from the entire upstream signal band Distributed according to the transmission request of al, it adjusts the transmission timing for each of the ONU so as to avoid collisions of the uplink signal, and a control unit for transmitting the gate on the transceiver. Here, “the ONU in which the length of the optical transmission path is a predetermined distance or more” and “ONU in the distance” are the long-range ONUs, and “the length of the optical transmission path is close to a predetermined distance or less. “ONU” and “close ONU” are short distance ONUs. In addition, the allocation period is determined by a request for an OLT processing time, a delay time, or the like.

  The optical communication system according to the present invention includes the OLT and a plurality of ONUs connected to the transmission / reception unit of the OLT through the optical transmission path.

  In the dynamic bandwidth allocation method according to the present invention, in the optical communication system, the OLT receives from the ONU a report including an uplink signal transmission request amount requested by the ONU, and permits transmission of the uplink signal to the ONU. When transmitting a gate including an amount and a transmission timing to the ONU, an allocation period of a predetermined time is determined in advance, and the upstream of the ONU with respect to an ONU in which the length of the optical transmission line is a predetermined distance or more A transmission permission amount is determined for each allocation cycle, and the upstream transmission permission amount of one allocation cycle for an ONU whose length of the optical transmission line is close to less than a predetermined distance among the ONUs From the ONU that is in close proximity to the ONU in the distant destination that is scheduled to be received in the one allocation cycle and has a reduced bandwidth for the upstream transmission permission amount. Distributed in accordance with the transmission demand, and adjusting the transmit timing for each of the ONU so as to avoid collisions of the uplink signal, and transmits the gate from the OLT.

  In this OLT and the dynamic bandwidth allocation method, when an upstream bandwidth is dynamically allocated to an ONU, a bandwidth predicted in advance is allocated to a remote ONU that cannot notify transmission permission for a transmission request within a predetermined time, The remaining bandwidth is allocated to the adjacent ONUs that can notify the transmission permission for the request within a predetermined time. For this reason, it is not necessary to match the allocation period to the RTT of the farthest ONU, and the delay time of the ONU having a small RTT does not become long.

  Accordingly, the present invention provides an OLT, an optical communication system, and a dynamic band allocation method capable of shortening a delay time while maintaining high band utilization efficiency when dynamically assigning an upstream band of a PON. it can.

  In the present invention, the OLT receives the report within an allocation period in which the adjacent ONU transmits the report, calculates a transmission permission amount and a transmission permission timing based on the received report, and transmits the transmission permission amount. And a length of the optical transmission line that allows the ONU to receive the gate within the same allocation cycle as the allocation cycle in which the ONU transmits the report. be able to.

  In the present invention, the predetermined distance may be the length of the optical transmission line having a round trip time (RTT) of a predetermined value.

  Further, in the present invention, the predetermined distance can be set to zero. It is also possible to perform bandwidth allocation in advance for all ONUs in the same manner as the long-distance ONU. In this case, the bandwidth utilization efficiency is slightly reduced, but the effect of shortening the delay is obtained.

  In the present invention, the uplink transmission permission amount for the remote ONU can be determined based on the change amount of the transmission request amount requested by the remote ONU.

  In the present invention, the amount of uplink signal communication from the distant ONU is monitored, and the amount of change in the transmission request amount requested by the distant ONU is set as the uplink transmission permission amount for the distant ONU. It may also be determined based on the traffic of the uplink signal being monitored.

  In the present invention, it is possible to set a maximum value of the uplink transmission permission amount for the ONU located in the distance and always set the uplink transmission permission amount for the ONU located in the distance to be equal to or less than the maximum value. SLA can be realized.

  In the present invention, the maximum value of the permitted uplink transmission amount for the remote ONU may be determined based on the number of ONUs.

  In the present invention, the maximum value of the permitted amount of uplink transmission for the ONU located far away may be determined based on the actual traffic amount received by the OLT.

  The present invention can provide an OLT, an optical communication system, and a dynamic band allocation method capable of shortening a delay time while maintaining high band utilization efficiency when dynamically assigning an upstream band of a PON.

It is a conceptual diagram explaining the standard specification of 10G-EPON. It is an example of the time diagram of the gate in the optical communication system which concerns on this invention, a report, and upstream data. 5 is a flowchart illustrating a dynamic bandwidth allocation method according to the present invention. It is the schematic which shows the relationship between the initial value of the allocation possible amount in the allocation period 2 of FIG. 2, the allocation amount already allocated to long-distance ONU, and the allocation amount which is not allocated.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(First embodiment)
The PON system of the present embodiment includes an OLT and a plurality of ONUs connected to the OLT transmission / reception unit via an optical transmission line. In this system, upstream communication is realized by TDM (time division multiple access). The ONU transmits uplink data only in accordance with transmission permission (transmission permission amount and transmission timing) from the OLT.

  The OLT is connected to a plurality of ONUs through an optical transmission line, receives a report including the requested transmission amount of the upstream signal requested by the ONU from the ONU, and includes a gate including the permitted transmission amount and transmission timing of the upstream signal for the ONU. A transmission / reception unit that transmits to the ONU and an allocation cycle of a predetermined time are determined in advance, and an uplink transmission permission amount for an ONU (far-distance ONU) in which the length of the optical transmission path is a predetermined distance or more in the ONU is allocated An uplink transmission permission amount for one allocation period for an ONU (short-distance ONU) in which the length of the optical transmission line is close to less than a predetermined distance in the ONU is determined from the entire bandwidth of the upstream signal. Distributes the bandwidth obtained by reducing the upstream transmission allowance for distant ONUs that are scheduled to be received periodically and according to the transmission request amount from nearby ONUs to avoid upstream signal collisions It adjusts the transmission timing for each ONU in so that comprises a control unit for transmitting a gate to the transceiver unit.

  In addition, the control unit receives the report within the allocation cycle in which the near-field ONU has transmitted the report, calculates the transmission permission amount and the transmission permission timing based on the received report, and sends a gate describing these, The length of the optical transmission line in which the ONU can receive the gate within the same assignment period as the assignment period in which the ONU has transmitted the report can be a predetermined distance. In addition, the control unit may set the predetermined distance as the length of the optical transmission line that has a predetermined value of RTT.

  FIG. 2 shows an example of the exchange of gates and reports and upstream data between the OLT and the ONU. In FIG. 2, Rx and Tx are a receiver and a transmitter of the OLT and ONU transmission / reception units, respectively. FIG. 3 is a diagram for explaining a dynamic bandwidth allocation method performed by this system, and shows a procedure for the OLT to notify each ONU of transmission permission.

  The exchange of gates and reports and uplink data between the OLT and ONU shown in FIG. 2 will be described. An ONU that can exchange a gate and a report within a predetermined allocation cycle (108) is called a short-distance ONU, and an ONU that cannot exchange a gate and a report within the allocation cycle is called a long-distance ONU. In this method, for a short-distance ONU, the OLT receives the report (101), calculates the transmission permission amount based on the transmission request amount notified by the report, and then transmits the transmission permission by the gate (103). Notify the amount and transmission permission timing. The short distance ONU transmits the uplink data (105) according to the notified transmission permission amount and transmission permission timing. For long-distance ONUs, allocation is performed in advance so that data can be transmitted every allocation period. At this time, the transmission permission amount allocated to the long-distance ONU is not based on the transmission request amount notified by the report, and notifies the value calculated by the OLT independently.

  The gate (104) to the long-distance ONU transmits at every assigned period, such as 104-1, 104-2, 104-3. The uplink data (107) permitted to be transmitted by the gates 104 is transmitted from the ONU according to the transmission permission timing notified by the respective gates. Here, the transmission permission timing notified by the gate 104 is designated to be received in the allocation period (preceding period) three cycles ahead of the gate transmission. That is, the long-distance ONU transmits the upstream data 107-4 by the transmission permission of the gate 104-1. It should be noted that how far in advance the preceding cycle (three cycles ahead) is set by the operator according to the connection distance of the long-distance ONU, and the present invention is limited by this value. is not.

  A procedure for the OLT shown in FIG. 3 to notify each ONU of transmission permission will be described. This procedure is performed for each period in which bandwidth allocation is repeated. This procedure starts from the time when report reception from the ONU is completed. Also, according to this procedure, the transmission permission amount and transmission timing of the next allocation cycle are calculated and notified to each ONU. If it is the 2nd period of FIG. 2, a procedure will be started from the time when reception of the reports 101-2 to 102-2 was completed, and the calculated results will be notified to each ONU as gates 103-2 to 104-2.

A specific procedure will be described below. First, the OLT subtracts from the initial value the sum ΣG _F ′ of the allocation amount already allocated to the long-distance ONU from the initial allocation value r ₀ of the next allocation cycle, and calculates the remaining allocation r. (Step S11). That is, r = r ₀ −ΣG _F ′. For example, in the case of the time in the second period of FIG. 2, as shown in FIG. 4, the current time is 201 and a part of the third period excluding the report allocation (202) (allocation to the long-distance ONU) The sum ΣG _F ′ (203) of the quantity G _F ′ has already been assigned to the long-distance ONU. Here, the data D _l (205) from the long-distance ONU _l has already been allocated. Therefore, the remaining unassigned r (204) is assigned as the uplink data transmission band of the short-distance ONU in the following procedure.

  Next, the OLT determines the allocation order P (i) for all ONUs (step S12). The allocation order P (i) is determined based on a cumulative average of actual transmission amounts of each ONU, a transmission request amount, an SLA such as a contract bandwidth, and the like.

Thereafter, the steps from Step S15 to Step S22 are repeated for all ONUs in the order of younger ONUs in the allocation order P (i). In the loop, first, it is determined whether or not the RTU of the ONU in the corresponding allocation order is larger than a predetermined value T (step S15). If RTT is equal to or less than T in step S15, it is determined whether a report from the corresponding ONU has been received (step S16). When receiving the report in step S16, it reads the transmission demand _{R k} (step _{S17), R k,} calculates a transmission permission amount _{G Nk} than r (step S18). If r> R _k, G _Nk = R _k , and if r ≦ R _k, G _Nk = r. When G _Nk is determined, the remaining allocatable amount r is updated as r = r−G _Nk (step S19), and then the transmission permission timing of the short-distance ONU is calculated (step S20). The initial value of the transmission permission timing of the short-distance ONU is the time when the time for receiving the allocation to the long-distance ONU that has already been allocated before the previous period has elapsed from the start time of the allocation cycle. It is calculated by adding the time required to transmit the permitted transmission amount. The calculation method of the transmission permission timing shown here shall be determined by the business operator according to the service provision policy, and the present invention is not limited to the calculation method of the transmission permission timing. After calculating the transmission permission timing, the process proceeds to the ONU of the next allocation order P (i) (step S23, step S24).

  In step S15, an upstream data transmission band is allocated several cycles ahead to a long-distance ONU having an RTT larger than T. Specifically, the OLT determines the allocation amount to the long-distance ONU (step S21), calculates the transmission permission timing of the long-distance ONU (step S22), and proceeds to the ONU of the next allocation order P (i). (Step S23, Step S24). The transmission permission timing of the long-distance ONU has an initial value of the start time of the allocation cycle in which uplink data from the long-distance ONU can be received by the transmission permission notified by the gate transmitted in the current allocation cycle. It is calculated by adding the transmission permission amount to.

  Further, the short distance ONU that has not received the report in step S16 does not perform the data transmission permission allocation, and proceeds to the ONU in the next allocation order P (i) (step S23, step S24). After following the above procedure for all ONUs connected to the OLT, gates are sent to all ONUs (step S25), and the process ends.

  In addition to the uplink data transmission band, an uplink band for causing each ONU to transmit a report may be allocated.

  When the RTT is larger than T, there are the following two methods for calculating the transmission permission amount when the OLT calculates the transmission permission amount in step S21. In Method 1, the uplink transmission permission amount for the long-distance ONU is determined based on the change amount of the transmission request amount requested by the long-distance ONU. In the method 2, the traffic amount of the upstream signal from the long-distance ONU is monitored, and the upstream transmission permission amount for the long-distance ONU is determined by the change amount of the transmission request amount requested by the long-distance ONU and the upstream signal being monitored. It is determined based on the traffic volume.

  In either method, in order to realize SLA, the control unit sets a maximum value Gmax and a minimum value Gmin of the uplink transmission permission amount for the long-distance ONU, and always sets the uplink transmission permission amount for the long-distance ONU to Gmin or more Gmax. The following. That is, the transmission permission amount G calculated by the method 1 or 2 is G = Gmin when G <Gmin, and G = Gmax when G> Gmax. The control unit may determine the value of Gmax based on the number of registered ONUs, the actual traffic amount observed by the OLT, or both the registered ONU number and the actual traffic amount.

An example of the allocation amount calculation method in Method 1 is shown below. The report amount received in the previous cycle is R0, the report amount received in the current cycle is R, and the time change amount of the report amount is DR = R−R0. For example, in the second period of FIG. 2, R0 is the transmission request amount notified from the long-distance ONU _{1 at} 102-1 and R is the transmission request notified from the long-distance ONU _{1 at} 102-2. Means quantity. When the absolute value of DR is larger than the absolute value of a predetermined value (A or B), the allocation amount G of the current cycle is changed from the allocation amount G0 of the previous cycle by DG _A or DG _B.
In particular,
G = G0 + DG _A (DR> A (A> 0))
G = G0−DG _B (DR <B (B <0))
G = G0 (B ≤ DR ≤ A)
And
With this method, the allocation amount can be changed in accordance with the change in the transmission request amount, and the frame loss prevention effect due to the buffer overflow can be obtained.

An example of the allocation amount calculation method in Method 2 is shown below. Similarly to the above, let DR = R−R0 be the amount of time change in the report amount. In addition, the amount actually transmitted by the ONU in the previous cycle excluding report transmission is U0, and the difference between the request amount and the actual transmission amount in the previous cycle is RE = R0−U0. If the second period in FIG. 2 is taken as an example, the actual transmission amount U0 means the data amount of the uplink data 107-1. Further, R and R0 mean the transmission request amount notified in 102-1 and the transmission request amount notified in 102-2, respectively, as described above. When DR and RE are larger than a predetermined value (C or D), the allocation amount G of the current cycle is changed from the allocation amount G0 of the previous cycle by DG _C or DG _D.
In particular,
G = G0 + DG _C (DR> C (C> 0))
_{G = G0 - DG D (RE} > D (D> 0))
G = G0 (DR ≦ C and RE ≦ D)
And

DG _A , DG _B , DG _C, and DG _D are set in advance by the operator so that buffer overflow does not occur and bandwidth utilization efficiency is not significantly reduced. For the purpose of preventing buffer overflow, it is desirable that DG _A > A and DG _C > C. As a specific setting example, DG _A = 1522, DG _B = 500, A = 1000, and B = −600 are set in order to cope with a certain amount of traffic change. With this method, it is possible to obtain the effect of preventing frame loss due to buffer overflow and the effect of preventing reduction in bandwidth utilization efficiency by preventing excessive allocation.

(Other embodiments)
In the optical communication system according to the first embodiment, as shown in FIG. 2, the ONU is divided into a long-distance ONU and a short-distance ONU, and a band is dynamically allocated. On the other hand, the control unit may set the predetermined distance divided into the long distance ONU and the short distance ONU to zero. Bandwidth allocation can be performed in advance by setting all ONUs as long-distance ONUs. In this case, the band use efficiency is lowered, but the effect of shortening the delay is obtained.

101, 101-1, 101-2, ...: Reports 102, 102-1, 102-2, ...: Reports 103, 103-1, 103-2, ...: Gates 104, 104-1 , 104-2,...: Gates 107, 107-1, 107-2,...: Uplink data 108: Allocation cycle 201: Current time 202: Report allocation bandwidth 203: Allocation bandwidth amount to long-distance ONU Sum 204: Remaining bandwidth 205: Upstream data from long-distance ONU

Claims (19)

It is connected to a plurality of optical subscriber units (ONU: Optical Network Unit) through an optical transmission line, receives a report including the requested transmission amount of the upstream signal requested by the ONU from the ONU, and transmits the upstream signal to the ONU. A transmission / reception unit for transmitting a gate including a transmission permission amount and a transmission timing to the ONU;
An allocation cycle for a predetermined time is determined in advance, and the uplink transmission permission amount for an ONU in which the length of the optical transmission line is far beyond a predetermined distance among the ONUs is determined for each allocation cycle, The transmission permitted for the ONU whose transmission path length is close to less than a predetermined distance is scheduled to be received in the one allocation period from the entire upstream band of the uplink signal. The transmission timing is distributed to each ONU so as to avoid a collision of uplink signals by distributing a band obtained by reducing the uplink transmission permission amount for the ONU located in the distance according to the transmission request amount from the adjacent ONU. And a control unit that causes the transmission / reception unit to transmit the gate;
An optical terminal device (OLT: Optical Line Terminal). The controller is
The report is received within the allocation period in which the adjacent ONU has transmitted the report, the transmission permission amount and the transmission permission timing are calculated based on the received report, and the transmission permission amount and the transmission permission timing are described. The length of the optical transmission line in which the ONU can receive the gate within the same allocation period as the allocation period in which the ONU transmits the report is defined as the predetermined distance. Item 2. The OLT according to Item 1. The controller is
2. The OLT according to claim 1, wherein the predetermined distance is a length of the optical transmission line having a round trip time (RTT) having a predetermined value. The controller is
The OLT according to claim 1, wherein the predetermined distance is 0. The controller is
5. The OLT according to claim 1, wherein the uplink transmission permission amount for the remote ONU is determined based on a change amount of the transmission request amount requested by the remote ONU. . The controller is
The amount of upstream signal transmission from the remote ONU is monitored, and the upstream transmission permission amount for the remote ONU is monitored by monitoring the amount of change in the transmission request amount requested by the remote ONU. The OLT according to any one of claims 1 to 4, wherein the OLT is determined based on a traffic amount of an uplink signal. The controller is
The maximum value of the uplink transmission permission amount for the remote ONU is set, and the uplink transmission permission amount for the remote ONU is always equal to or less than the maximum value. OLT as described in. The controller is
The OLT according to claim 7, wherein a maximum value of the permitted amount of uplink transmission for the ONU located far away is determined based on the number of the ONUs. The controller is
The OLT according to claim 7, wherein a maximum value of the uplink transmission permission amount for the ONU located in a distant place is determined based on an actual traffic amount received by the transmission / reception unit. OLT according to any of claims 1 to 9,
A plurality of ONUs connected to the transmission / reception unit of the OLT via the optical transmission line;
An optical communication system. In a dynamic bandwidth allocation method of a communication system in which an OLT and a plurality of ONUs are connected by an optical transmission line,
When the OLT receives a report including the requested transmission amount of the uplink signal requested by the ONU from the ONU and transmits a gate including the permitted transmission amount and transmission timing of the uplink signal to the ONU to the ONU.
An allocation cycle for a predetermined time is determined in advance, and the uplink transmission permission amount for an ONU in which the length of the optical transmission line is far beyond a predetermined distance among the ONUs is determined for each allocation cycle, The transmission permitted for the ONU whose transmission path length is close to less than a predetermined distance is scheduled to be received in the one allocation period from the entire upstream band of the uplink signal. The transmission timing is distributed to each ONU so as to avoid a collision of uplink signals by distributing a band obtained by reducing the uplink transmission permission amount for the ONU located in the distance according to the transmission request amount from the adjacent ONU. A dynamic bandwidth allocation method for adjusting the frequency and transmitting the gate from the OLT.   The OLT receives the report within an allocation period in which the ONU whose length of the optical transmission path is close to less than a predetermined distance transmits the report, and sets the transmission permission amount and the transmission permission timing based on the received report. Calculating and sending a gate that describes the transmission permission amount and the transmission permission timing, and the ONU can receive the gate within the same allocation cycle as the allocation cycle in which the ONU has transmitted the report. The dynamic bandwidth allocation method according to claim 11, wherein a length is set as the predetermined distance.   The dynamic band allocation method according to claim 11, wherein the predetermined distance is a length of the optical transmission line having a round trip time (RTT) having a predetermined value.   The dynamic band allocation method according to claim 11, wherein the predetermined distance is set to zero.   The operation according to any one of claims 11 to 14, wherein the uplink transmission permission amount for the remote ONU is determined based on a change amount of the transmission request amount requested by the remote ONU. Bandwidth allocation method.   The amount of upstream signal transmission from the remote ONU is monitored, and the upstream transmission permission amount for the remote ONU is monitored by monitoring the amount of change in the transmission request amount requested by the remote ONU. The dynamic band allocation method according to claim 11, wherein the dynamic band allocation method is determined based on a traffic amount of an uplink signal.   17. The maximum uplink transmission permission amount for the remote ONU is set, and the uplink transmission permission amount for the remote ONU is always equal to or less than the maximum value. The dynamic bandwidth allocation method described in 1.   The dynamic band allocation method according to claim 17, wherein a maximum value of the uplink transmission permission amount for the remote ONU is determined based on the number of the ONUs.   18. The dynamic band allocation method according to claim 17, wherein the maximum value of the uplink transmission permission amount for the ONU located in a distant place is determined based on the actual traffic amount received by the OLT.

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