JP5421306B2 - Data communication system, buffer control device, and buffer control method - Google Patents

Description

  The present invention relates to a data communication technique, and more particularly, to a buffer control technique for data transmitted from a transmission source network apparatus to a transmission destination network apparatus.

  In an optical data communication system such as a PON system, in many cases, the communication speed of the UNI (User Network Interface) in the network device on the data receiving side is lower than the communication speed in the optical communication section. It is necessary to provide a large-capacity buffer in the network device on the side.

FIG. 7 is an explanatory diagram showing a buffer configuration in a conventional PON system.
An ONU (Optical Network Unit: subscriber side device) is provided with an upstream buffer and a downstream buffer, and data (packets) received via the UNI are transmitted via the upstream buffer to an OLT (Optical Line Terminal: station). The data received from the OLT and transmitted from the OLT is transmitted to the UNI via the downlink buffer. Similarly, the OLT is provided with an upstream buffer and a downstream buffer, and data received from the ONU is transmitted to the NNI (Network Network Interface) via the upstream buffer, and data received from the NNI. Is transmitted to the ONU via the downlink buffer.

  The ONU downstream buffer requires a particularly large buffer and consumes a large amount of power. As a method for saving power in the ONU downstream buffer, the method of Non-Patent Document 1 has been proposed. This method consists of two methods: a combined buffer method applied to the ONU downstream buffer and a bandwidth control method applied to the OLT downstream buffer.

FIG. 8 is an explanatory diagram showing a downlink buffer configuration in a PON system to which the conventional bandwidth control method and the combined buffer method are applied.
The ONU downstream buffer includes an internal buffer with a small capacity and a low power consumption, an external buffer with a large capacity and a high power consumption, and a buffer control circuit for controlling accumulation in both buffers. In the non-patent document 1, the ONU combined buffer method saves power in the downstream buffer of the ONU by switching the buffer according to the sum of the accumulated amounts of both buffers (hereinafter referred to as the buffer accumulated amount).

  The internal buffer has a specified capacity and a start-up area capacity. The capacity of the specified value is the capacity that the ONU provides for power saving. When the buffer storage amount is small, the downlink data addressed to the ONU is stored only by the capacity, the external buffer is stopped, and the ONU download Save power in the buffer. The capacity for the activation area is the capacity of the activation area used for the ONU to accumulate data input during the activation process of the external buffer.

  In this combined buffer method, the buffer control circuit measures the buffer accumulation amount, and when the measured value exceeds a specified value, the buffer control circuit instructs the activation of the external buffer. When receiving the instruction, the external buffer starts the activation process. During the activation process of the external buffer, the ONU accumulates data in the activation area, and accumulates data in the external buffer when activation of the external buffer is completed. In Non-Patent Document 1, in addition to using this combined buffer method, a band control method is applied to the OLT in order to further reduce the activation area and minimize the internal buffer capacity that is a factor of cost increase.

  In the bandwidth control method, when an external buffer included in an ONU is being activated, the OLT limits the downlink data rate addressed to the ONU. With this method, when the external buffer included in the ONU is in the process of starting, the amount of downlink data received by the ONU decreases, and the amount of data stored in the ONU buffer decreases. Can be reduced.

FIG. 9A is an explanatory diagram showing the operation of the OLT downlink buffer (normal time), and FIG. 9B is an explanatory diagram showing the operation of the OLT downlink buffer (when the external buffer is activated).
As shown in FIG. 9A, the OLT normally transmits downlink data to the ONU without limiting the downlink data rate to the ONU. On the other hand, when the OLT determines that the external buffer included in the ONU is being activated, as shown in FIG. 9B, the downlink data rate addressed to the ONU is measured until the pre-measured activation time of the external buffer elapses. Limit.

  The OLT calculates an estimated value of the ONU buffer accumulation amount. The estimated value of the ONU buffer storage amount is calculated from the integrated value (unit: Bytes) of downlink data addressed to the ONU, and the amount of Bytes that the ONU can output to the UNI per unit time (8 × UNI transmission rate [ bit / s] × unit time). However, the unit time is, for example, one clock cycle time of the ONU protocol control LSI.

  When the estimated value calculated in this way exceeds the specified value, the OLT determines that the external buffer included in the ONU is being activated, and starts limiting the downlink data rate. The limitation on the downlink data rate is maintained until the activation processing time of the external buffer elapses, and the limitation on the downlink data rate is terminated after the activation processing time has elapsed.

FIG. 10 is an explanatory diagram showing the buffer accumulation operation of the ONU to which the conventional bandwidth control method and the combined buffer method are applied. FIG. 10 (a) is the downlink data received by the ONU, and FIG. 10 (b) is the ONU. The type of buffer in which data is stored and the buffer storage amount are shown. In FIG. 10, the horizontal axis represents time, and the vertical axis in FIG. 10B represents the buffer accumulation amount.
When the OLT applies the bandwidth control method, the downlink data rate is limited while the external buffer included in the ONU is being activated, and the amount of increase in the ONU buffer accumulation amount is reduced. As a result, the ONU can reduce the capacity of the internal buffer by reducing the activation area. If the communication speed at the time of limiting the downlink data rate is Sshap [Byte / s] and the startup processing period length of the external buffer is Tw, the capacity [byte] of the startup area can be obtained by Sshap × Tw.

Published by Hiroyuki Serizawa et al., “Examination of ONU buffer power saving method”, B-8-19, 2010 Society Conference, IEICE, 2010-8-31.

  In the bandwidth control method of Non-Patent Document 1 described above, it is important in the OLT to accurately grasp whether or not the ONU external buffer is being activated. This is because if the start time of the external buffer start-up process in the ONU does not match the limit start time of the downlink data rate in the OLT, it cannot be accumulated in the start-up area provided in the ONU, and data loss occurs in the ONU. Because.

For this reason, in Non-Patent Document 1, when the ONU receives a PAUSE frame from the UNI and the ONU stops data transmission to the UNI, the OLT can accurately grasp whether or not the external buffer included in the ONU is being activated. However, there is a problem that data loss occurs.
When the ONU stops data transmission to the UNI, the start time of the external buffer start processing at the ONU is earlier than the start start time of the downlink data rate at the OLT, and the ONU is in the process of starting the external buffer. This occurs because it is impossible to store all the data input to the area only with the activation area.

  That is, in the conventional bandwidth control method, the OLT calculates an estimated value of the ONU buffer accumulation amount, and when the estimated value exceeds a specified value, the external buffer included in the ONU is determined to be in the startup process and the downlink data rate is set. Restrict. In the calculation of the estimated value, the ONU is always calculated on the assumption that data is continuously transmitted to the UNI at the UNI transmission rate. For this reason, when the ONU receives a PAUSE frame from the UNI and the ONU stops data transmission to the UNI, the above assumption is not satisfied, so the time when the actual buffer storage amount exceeds the specified value is It is earlier than the time when the estimated value of the buffer accumulation amount in the OLT exceeds the specified value.

  This means that the external buffer activation process start time in the ONU is earlier than the downlink data rate restriction start time in the OLT, and there is a time during which the downlink data rate is not limited even during the external buffer activation process. For this reason, in the activation area alone, the capacity is insufficient to accumulate all data input during the activation process of the external buffer, and data loss occurs.

FIG. 11 is a diagram illustrating an example of ONU buffer accumulation operation (when the activation area is insufficient).
In FIG. 11, Tw [s] is the length of the external buffer activation processing period included in the ONU, ΔT [s] is the time difference between the actual ONU buffer accumulation amount and its estimated value exceeding the specified value, and Spon [Byte / s] is the maximum value of the downlink data rate communication speed, and Sshap [Byte / s] is the communication speed when the downlink data rate is limited. When the bandwidth control method is applied, while the external buffer provided in the ONU is in the startup process, the downstream data rate of the ONU is limited by the OLT, and the communication speed of the downstream data rate received by the ONU becomes Sshap. Based on the premise, the capacity of the activation area is determined.

  However, as shown in FIG. 11, when the limit start time of the downlink data rate in the OLT is delayed by ΔT from the start time of the external buffer activation process in the ONU, the downlink received by the ONU during the ΔT The maximum data rate is Spon. For this reason, in order for the ONU to accumulate all data input during the activation process of the external buffer, in addition to the activation area, an additional capacity required for preventing data loss is required. The capacity ΔN is a value obtained by (Spon−Sshap) × ΔT.

  As described above, in Non-Patent Document 1, the capacity provided for the ONU to store data input during the startup process of the external buffer is only the startup area. Since ΔN is not provided, the capacity is insufficient and data loss occurs.

  The present invention is to solve such a problem, and the data loss caused by the time difference between the start time of the external buffer activation process at the receiving side network device and the start time of the downlink data rate limit at the transmitting side network device. An object of the present invention is to provide a buffer control technique capable of preventing the occurrence.

  In order to achieve such an object, a data communication system according to the present invention includes a first network device that sequentially reads and transmits data temporarily stored in a transmission buffer, and a first network device via a transmission line. When the arrival data received from the network device is sequentially accumulated in the reception buffer, the arrival data from the first buffer to the second buffer in the reception buffer is increased in accordance with the increase in the data accumulation amount in the reception buffer. A second network device that switches a storage destination of the second network device, and the first network device monitors the data read from the transmission buffer and transmitted to the second network device, thereby receiving the second network device. Data accumulation estimated by the transmission side accumulation amount estimation unit that estimates the data accumulation amount in the buffer and the transmission side accumulation amount estimation unit An activation detection unit that detects when the estimated value indicating the value exceeds a predetermined specified value as the activation process start time of the second buffer in the second network device, and from the activation process start time detected by the activation detection unit A data rate control unit for limiting a transmission data rate of data to be read from the transmission buffer and transmitted to the second network device over an activation process period length required for the activation process of the second buffer; The device monitors the arrival data input to the reception buffer to estimate the data accumulation amount in the reception buffer, and the accumulation amount measurement to measure the actual data accumulation amount in the reception buffer. And the estimated value of the data accumulation amount estimated by the accumulation amount estimation unit and the measurement value of the data accumulation amount measured by the accumulation amount measurement unit The reserve capacity for accumulating arrival data input during these times is calculated, and the reference value obtained by subtracting the reserve capacity from the specified value is used as the estimated or measured value. When at least one of them exceeds the activation control unit for starting the activation process for changing the second buffer from the disabled state to the usable state, and the storage destination of the arrival data from the first buffer to the second buffer A switching control unit that switches the storage destination to the second buffer when the measured value exceeds the specified value and the activation process is completed.

  At this time, the start control unit calculates the time change amount S1 of the measured value and the time change amount S2 of the estimated value during the predetermined time Ts for each predetermined time Ts. If S1 is 0 or less, the reference value If S1 is greater than 0 and S2 is greater than 0, the difference between the time T1 when the measured value reaches the specified value and the time T2 when the estimated value reaches the specified value is expressed as a time difference ΔT. When S1 is larger than 0 and S2 is 0 or less, the activation processing period length Tw of the second buffer is set as the time difference ΔT, and the maximum transmission data rate Spon in the first network device and the first network The spare capacity ΔN is calculated by multiplying the difference from the transmission data rate Sshap under the restriction of the transmission data rate in the apparatus by the time difference ΔT, and the obtained spare capacity ΔN is subtracted from the specified value. You may make it set as a quasi-value.

  Further, when the estimated value exceeds the specified value by the activation detection unit, a limit start notification indicating the start of limiting the transmission data rate is transmitted to the second network device, and the switching control unit receives the limit start notification. In response, an activation process for making the second buffer usable is started.

  In addition, the buffer control device according to the present invention sequentially reads and transmits the data temporarily stored in the transmission buffer, and sets the estimated data storage amount in the reception buffer of the second network device to be a communication partner. Based on the first network device that controls the transmission data rate of data to be transmitted to the second network device, the second network device that sequentially stores the arrival data that has arrived via the transmission path in the reception buffer is provided. And a buffer control device that switches the storage destination of arrival data from the first buffer to the second buffer in the reception buffer in accordance with an increase in the amount of data stored in the reception buffer. Estimate the amount of data stored in the receiving buffer by monitoring the arrival data input to A storage amount measurement unit that measures the actual data storage amount in the receiving buffer, a data storage amount estimation value estimated by the storage amount estimation unit, and a data storage amount measurement value measured by the storage amount measurement unit Predicts the time when it reaches a predetermined specified value, calculates a reserve capacity for accumulating arrival data input during these times, and calculates a reference value obtained by subtracting the reserve capacity from the specified value, When at least one of the estimated value and the measured value exceeds, the activation control unit that starts the activation process for changing the second buffer from the disabled state to the usable state, and the storage destination of the arrival data are When switching from one buffer to the second buffer, a switching control unit is provided that switches the accumulation destination to the second buffer when the measured value exceeds the specified value and the activation process is completed.

  At this time, the start control unit calculates the time change amount S1 of the measured value and the time change amount S2 of the estimated value during the predetermined time Ts for each predetermined time Ts. If S1 is 0 or less, the reference value If S1 is greater than 0 and S2 is greater than 0, the difference between the time T1 when the measured value reaches the specified value and the time T2 when the estimated value reaches the specified value is expressed as a time difference ΔT. When S1 is larger than 0 and S2 is 0 or less, the activation processing period length Tw of the second buffer is set as the time difference ΔT, and the maximum transmission data rate Spon in the first network device and the first network The spare capacity ΔN is calculated by multiplying the difference from the transmission data rate Sshap under the restriction of the transmission data rate in the apparatus by the time difference ΔT, and the obtained spare capacity ΔN is subtracted from the specified value. You may make it set as a quasi-value.

  In addition, the switching control unit starts an activation process for making the second buffer usable in response to reception of a restriction start notification indicating start of restriction of the transmission data rate from the first network device. May be.

  In addition, the buffer control method according to the present invention sequentially reads and transmits data temporarily stored in the transmission buffer, and sets an estimated value of the data storage amount in the reception buffer of the second network device serving as a communication partner. Based on the first network device that controls the transmission data rate of the data to be transmitted to the second network device, the second network device sequentially accumulates the arrival data received via the transmission path in the reception buffer. A buffer control method for switching the storage destination of arrival data from the first buffer to the second buffer in the reception buffer in accordance with an increase in the data storage amount in the reception buffer. Monitor the amount of data stored in the reception buffer by monitoring the arrival data input to the reception buffer. An accumulation amount estimation step, an accumulation amount measurement unit that estimates an actual data accumulation amount in the reception buffer, and an activation control unit that estimates an accumulation amount estimated in the accumulation amount estimation step. Predict the time when the measured value of the data accumulation amount measured in the value and accumulation amount measurement step reaches a predetermined specified value, calculate the reserve capacity for accumulating arrival data input during these times, and specify Activation to change the second buffer from the disabled state to the usable state when at least one of the estimated value and the measured value exceeds the reference value obtained by subtracting the reserve capacity from the value When the activation control step for starting the process and the switching control unit switch the storage destination of the arrival data from the first buffer to the second buffer, the measured value exceeds the specified value, and the activation process Upon completion, and a switching control step of switching the storage destination to the second buffer.

  At this time, the step of calculating the time change amount S1 of the measured value and the time change amount S2 of the estimated value during the predetermined time Ts in the start control step, and when S1 is 0 or less, A step of setting a specified value as a reference value, and when S1 is greater than 0 and S2 is greater than 0, a time T1 when the measured value reaches the specified value and a time T2 when the estimated value reaches the specified value A step in which the difference is a time difference ΔT, a step in which the activation processing period length Tw of the second buffer is a time difference ΔT when S1 is greater than 0 and S2 is 0 or less; The difference between the maximum transmission data rate Spon and the transmission data rate Sshap under the limitation of the transmission data rate in the first network device is multiplied by the time difference ΔT to obtain the reserve capacity ΔN. Out, the value obtained by subtracting from the reserve capacity ΔN by a specified value obtained may include a step of setting as a reference value.

  In addition, the switching control step includes a step of starting an activation process for making the second buffer usable in response to reception of a restriction start notification indicating a restriction start of a transmission data rate from the first network device. But you can.

  According to the present invention, the activation process of the second buffer can be started at a time prior to the start of transmission data rate restriction in the first network device. Therefore, it is possible to prevent the occurrence of data loss due to the time difference between the start processing start time of the second buffer in the receiving network device and the start time of limiting the transmission data rate in the first network device. Become.

It is a block diagram which shows the structure of the data communication system concerning 1st Embodiment. It is explanatory drawing which shows the change ((DELTA) T = 0) of buffer accumulation amount. It is explanatory drawing which shows the change ((DELTA) T> 0) of buffer accumulation amount. It is a flowchart which shows a reference value calculation process. It is a flowchart which shows a starting control process. It is a flowchart which shows a switching control process. It is explanatory drawing which shows the buffer structure in the conventional PON system. It is explanatory drawing which shows the downstream buffer structure in the PON system to which the conventional band control method and the combined buffer method are applied. It is explanatory drawing which shows the operation | movement (normal time) of the downlink buffer of OLT. It is explanatory drawing which shows operation | movement of the OLT downlink buffer (at the time of external buffer starting). It is explanatory drawing which shows the buffer storage operation | movement of ONU to which the conventional band control method and the combined buffer method are applied. It is an explanation showing an example of ONU buffer accumulation operation (when the activation area is insufficient).

Next, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
First, a data communication system 1 according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of a data communication system according to the first embodiment.

  This data communication system 1 includes an OLT (first network device) 10 that transmits data (packets) via a downlink buffer (transmission buffer) 11 and data from the OLT connected via a transmission line L. One or more ONUs (second network devices) that switch and store the internal buffer (first buffer) 22 and the external buffer (second buffer) 23 provided in the downlink buffer (reception buffer) 21 20.

In the present embodiment, a case where the data communication system 1 is applied to a PON system will be described as an example. However, the present invention is not limited to this, and can be applied to other general data communication systems as well.
In the following description, the transmission direction in which data is transmitted from the OLT to the ONU is referred to as downlink, and the transmission direction in which data is transmitted from the ONU to the OLT is referred to as uplink. In this embodiment, the case where the present invention is applied to the downstream direction from the OLT to the ONU will be described as an example. However, the present invention is not limited to this, and the present invention can be similarly applied to the upstream direction from the ONU to the OLT. It is.

In this embodiment, the OLT performs the same bandwidth control method as the conventional one, and the ONU newly implements the data loss prevention method in addition to the same combined buffer method as the conventional one.
Specifically, the OLT estimates the data accumulation amount in the ONU downlink buffer by monitoring the data read from the downlink buffer and transmitted to the ONU, and the estimated value indicating the estimated data accumulation amount exceeds the specified value. Is detected as the start time of the start-up process of the external buffer 23 performed for buffer switching in the ONU, and the transmission buffer extends over the start-up process period length Tw required for the start-up process of the external buffer 23 from the start time of the start-up process. The downstream data rate of the data read from and transmitted to the ONU is limited.

  Further, in the ONU, the amount of data stored in the down buffer is estimated by monitoring the arrival data input to the down buffer, and the actual amount of data stored in the reception buffer is measured. Predict the time to reach the specified value, calculate the reserve capacity for accumulating the arrival data input during these times, and subtract the reserve capacity from the specified value, the estimated value or When at least one of the measured values is exceeded, start processing for changing the second buffer from the use stop state to the usable state is started, and the storage destination of the arrival data is transferred from the internal buffer 22 to the external buffer 23. When switching, the storage destination is switched to the external buffer 23 when the measured value exceeds the specified value and the start-up process of the external buffer 23 is completed.

  According to the present embodiment, even when the external buffer activation process start time is earlier than the downlink data rate restriction start time in the OLT, the ONU stores all data input during the external buffer activation process in the internal buffer. Accumulation prevents data loss. In order to accumulate all data input during the startup process of the external buffer, the internal buffer needs a capacity required for preventing data loss in addition to the capacity of the startup area. The ONU in the present embodiment dynamically secures a spare area having a capacity necessary for preventing such data loss in the internal buffer. At this time, it is rare that the external buffer activation processing start time is delayed from the downlink data rate restriction start time, and thus a time difference ΔT is rarely generated. Data loss can be prevented while performing.

[OLT]
Next, the configuration of the OLT 10 used in the data communication system 1 according to the present embodiment will be described in detail with reference to FIG.
The OLT 10 is a network device that temporarily stores downlink data received from the NNI in a downlink buffer and transmits it to the ONUs that are the respective transmission destinations. The OLT 10 includes a downlink buffer 11, a downlink data rate control unit 12, an accumulation amount estimation unit 13, and an activation detection unit 14 as main functional units.

The downlink buffer 11 is made of, for example, a semiconductor memory and has a function of temporarily storing downlink data (packets) from the NNI.
The downlink data rate control unit 12 includes, for example, a dedicated communication circuit, and reads the downlink data read from the downlink buffer 11 and transmitted to each ONU according to the downlink data rate set for each ONU. In response to the function to be transmitted and the instruction from the activation detector 14, the ONU instructed over the activation process period length Tw required for the activation process of the external buffer 23 in the ONU from the activation process start point detected by the activation detector 14 And the function of limiting (reducing) the downlink data rate to the network.

  The accumulation amount estimation unit 13 is composed of, for example, a dedicated LSI, and monitors the downlink data output from the downlink data rate control unit 12 to the transmission line L individually for each ONU and the ONU based on the monitoring results. Each has a function of estimating the amount of data stored in the downstream buffer of the ONU.

  The activation detection unit 14 is made of, for example, a dedicated LSI, and for each ONU, a function for comparing the estimated value of the data accumulation amount estimated by the accumulation amount estimation unit 13 with a preset specified value Nw, and this function As a result of the comparison, a function for detecting when the estimated value for an arbitrary ONU exceeds a specified value as the start processing start time of the external buffer 23 in the ONU, and the ONU for the start processing period length Tw from the start processing start time And a function of instructing the downlink data rate control unit 12 to limit the downlink data rate. Note that the specified value Nw and the activation processing period length Tw may be those notified from the ONU to the OLT by negotiation at the start of communication.

[ONU]
Next, the configuration of the ONU 20 used in the data communication system 1 according to the present embodiment will be described in detail with reference to FIG.
The ONU 20 is a network device that temporarily stores downlink data (arrival data) reached from the OLT 10 via the transmission line L in the downlink buffer 21 and outputs it from the UNI. The ONU 20 is provided with a downstream buffer 21, switching units 24A and 24B, and a buffer control device 25 as main functional units.

  The downlink buffer 21 is made of, for example, a semiconductor memory and has a function of temporarily storing downlink data that has arrived from the OLT 10 via the transmission line L. The downstream buffer 21 is provided with two buffers, an internal buffer 22 and an external buffer 23, in parallel, and one of them is switched and selected by the switching unit 24A as a storage destination of downstream data (arrival data).

The internal buffer (first buffer) 22 is composed of a semiconductor memory having a smaller storage capacity and lower power consumption than the external buffer 23. For example, a memory built in a communication LSI (MAC LSI) is used.
The external buffer (second buffer) 23 is a semiconductor memory that has a larger storage capacity and power consumption than the internal buffer 22, and for example, a memory externally connected to a communication LSI (MAC LSI) is used. .

  In this embodiment, as a basic operation, when the downlink data is stored in the downlink buffer 21, the internal buffer 22 is preferentially used, and the downlink data is stored in accordance with the increase in the data storage amount in the downlink buffer 21. The destination is switched from the internal buffer 22 to the external buffer 23. Further, when the external buffer 23 is not used, the external buffer 23 is changed from the usable state to the unusable state by, for example, controlling the power supply to the external buffer 23 and the clock. Thereby, the power consumption of the whole downlink buffer 21 can be reduced.

The switching unit 24A is composed of a switching circuit such as a dedicated LSI, for example, and in accordance with a switching instruction from the buffer control device 25, downlink data stored in the downlink buffer 21 is transferred to either the internal buffer 22 or the external buffer 23. It has a function of switching input.
The switching unit 24B is formed of a switching circuit such as a dedicated LSI, for example, and in accordance with a switching instruction from the buffer control device 25, the downlink data stored in the downlink buffer 21 is transferred to either the internal buffer 22 or the external buffer 23. It has a function of switching output from one side.

  The buffer control device 25 has a function of performing switching control between the internal buffer 22 and the external buffer 23 of the downlink buffer 21. The buffer control device 25 is provided with an accumulation amount estimation unit 26, an accumulation amount measurement unit 27, an activation control unit 28, and a switching control unit 29 as main processing units. The accumulation amount estimation unit 26, the accumulation amount measurement unit 27, the activation control unit 28, and the switching control unit 29 constituting the buffer control device 25 are, for example, a communication LSI (MAC) together with the internal buffer 22 and the switching units 24A and 24B. It may be realized by one common LSI such as LSI).

The accumulation amount estimation unit 26 monitors the downlink data (arrival data) that has arrived from the OLT to the downlink buffer 21 via the transmission line L, and the data accumulation amount in the downlink buffer 21 based on the monitoring result, that is, the internal data It has a function of estimating the amount of data stored in both the buffer 22 and the external buffer 23 and outputting it as an estimated value Ne.
The accumulation amount measuring unit 27 monitors the downlink data (arrival data) that has arrived from the OLT to the downlink buffer 21 via the transmission line L, the function of monitoring the downlink data output from the downlink buffer 21, and this monitoring. Based on the result, it has a function of measuring the data accumulation amount in the down buffer 21, that is, the actual data accumulation amount in both the internal buffer 22 and the external buffer 23, and outputting the measurement value Nm.

  The activation control unit 28 has the estimated value Ne of the data accumulation amount related to the downlink buffer 21 obtained by the accumulation amount estimation unit 26 and the measurement value Nm of the data accumulation amount related to the downlink buffer 21 obtained by the accumulation amount measurement unit 27. A function of predicting times T1 and T2 reaching the specified value Nw, a function of calculating a reserve capacity ΔN for accumulating arrival data input during a period from the time T1 to the time T2, and the reserve from the specified value Nw A function for calculating the reference value Ns by subtracting the capacity, a function for comparing the estimated value Ne and the measured value Nm with the reference value Ns, and at least one of the estimated value Ne or the measured value Nm is a reference value. When Ns is exceeded (Ne> Ns or Nm> Ns), the start of the startup process for changing the external buffer 23 from the stopped state to the usable state is performed. And a function of outputting an activation process start instruction to instruct the 1.

  When the switching control unit 29 switches the storage destination of the arrival data from the internal buffer 22 to the external buffer 23 in accordance with an increase in the data storage amount in the downlink buffer 21, the measurement value Nm obtained by the storage amount measurement unit 27 is defined. It has a function of switching the storage destination to the external buffer 23 when the value Nw is exceeded (Nm> Nw) and the activation process of the external buffer 23 is completed. At this time, for switching from the internal buffer 22 to the external buffer 23, an external buffer switching instruction is output from the switching control unit 29 to the switching unit 24A.

The present invention relates to control for switching the storage destination of arrival data from the internal buffer 22 to the external buffer 23 in the down buffer 21 in accordance with an increase in the amount of data stored in the down buffer 21 of the ONU. For switching from 23 to the internal buffer 22, any switching control may be employed.
As an example of switching control from the external buffer 23 to the internal buffer 22, when it is detected that the measured value Nm becomes zero (Nm = 0), the switching control unit 29 changes the external buffer 23 to the internal buffer 22. You may make it switch. As another example of the switching control, a threshold value Nv having a data accumulation amount smaller than the specified value Nw is set in advance, and the switching control unit 29 causes the measured value Nm to be equal to or less than the threshold value Nv. When it is detected that the data accumulation amount Ng of the external buffer 23 obtained by the accumulation amount measuring unit 27 has become zero (Nm ≦ Nv and Ng = 0), the external buffer 23 is switched to the internal buffer 22. May be.

[Operation of First Embodiment]
Next, the operation of the data communication system 1 according to the present embodiment will be described with reference to FIGS. FIG. 2 is an explanatory diagram showing a change in the buffer accumulation amount (ΔT = 0). FIG. 3 is an explanatory diagram showing a change in the buffer accumulation amount (ΔT> 0). FIG. 4 is a flowchart showing the reference value calculation process. FIG. 5 is a flowchart showing the activation control process. FIG. 6 is a flowchart showing the switching control process.

  In the ONU downstream buffer 21, in order to prevent data loss caused by the activation delay of the external buffer 23, a reserve capacity ΔN for accumulating arrival data input during the activation delay period is provided in the internal buffer 22. It is necessary to secure it. The spare capacity ΔN is calculated by the ONU by calculating the time difference ΔT, and the ONU is dynamically secured in the internal buffer 22 based on the value of ΔT.

  ΔT is a time difference between a predicted start time T1 that is a predicted value of the start processing start time of the external buffer 23 in the ONU and a predicted start time T2 that is a predicted value of the downlink data rate limit start time in the OLT. . The ONU calculates T1 and T2 by linear interpolation every specified time Ts [s] from the measured value Nm indicating the actual buffer storage amount and the estimated buffer storage amount Ne calculated by the same method as the OLT. The time difference ΔT is calculated.

  The ONU calculates a reserve capacity ΔN required for preventing data loss based on the value of ΔT. Then, by setting the reference value Ns indicating the amount of data stored in the external buffer 23 to be activated to a value obtained by reducing the initial value stipulated value Nw by the reserve capacity ΔN, data loss can be performed separately from the activation area. A spare area having a spare capacity ΔN required for prevention is secured in the internal buffer 22, and data for this spare area is stored in the internal buffer 22. The initial value of the reference value Ns is a specified value Nw. When either the measured value Nm or the estimated value Ne of the buffer accumulation amount exceeds the reference value Ns, the ONU starts the activation process of the external buffer 23.

  When ΔT is 0, as shown in FIG. 2, since the reference value Ns is the same as the initial value, that is, the specified value Nw, the ONU is input during the start-up process of the external buffer 23 as in the prior art. All data to be stored is accumulated only in the activation area. On the other hand, when ΔT is positive, as shown in FIG. 3, the reference value Ns is lowered from the specified value Nw by the reserve capacity ΔN required for data loss prevention, and the data input during the startup process of the external buffer 23 is reduced. Accumulate in the spare area and the activation area. That is, the ONU accumulates all data input during the startup process of the external buffer 23 with the startup area and the reserve capacity ΔN required for preventing data loss.

  The ONU calculates the time difference ΔT and changes the reference value Ns by executing the data loss prevention process shown in FIG. 3 every specified time Ts [s] during data communication. At this time, the ONU lowers the reference value Ns based on ΔT only when T1 is earlier than T2. This is because the ONU according to the present embodiment starts the activation process of the external buffer 23 even when the estimated value Ne exceeds the reference value Ns. Therefore, if T1 is later than or equal to T2, the ONU 23 This is because the downstream data rate is always limited by the OLT during the startup process, and can be stored only in the startup area.

On the other hand, T1 may be earlier than T2 only when the amount of time change S1 of the buffer accumulation amount is positive. Therefore, in the reference value calculation process shown in FIG. 4, the activation control unit 28 first calculates the time of the measured value Nm based on the measured value Nm of the buffer accumulation amount related to the downlink buffer 21 obtained by the accumulation amount measuring unit 27. A change amount (slope) S1 is calculated (step 100). As shown in the following equation (1), S1 is calculated by dividing a value obtained by subtracting the past measurement value N′m from the current measurement value Nm by the time Ts by the time Ts.

なお、ステップ１００およびステップ１０１の処理順序については、これに限定されるものではなく、ステップ１０１を実行した後にステップ１００を実行してもよく、ステップ１００およびステップ１０１を並列的に実行してもよい。 Further, the activation control unit 28 calculates a temporal change amount (slope) S2 of the estimated value Ne based on the estimated value Ne of the buffer accumulation amount related to the downlink buffer 21 obtained by the accumulation amount estimation unit 26 (step 101). . As shown in the following equation (2), S2 is calculated by dividing a value obtained by subtracting the past estimated value N′e from the current estimated value Ne by the time Ts by the time Ts.

Note that the processing order of step 100 and step 101 is not limited to this, step 100 may be executed after step 101 is executed, and step 100 and step 101 may be executed in parallel. Good.

  Here, when S1 is 0 or less (step 102: NO), the activation control unit 28 sets the reference value Ns as the initial value Nw without calculating T1 and T2 (step 110), and performs a series of reference value calculation processes. finish. As a result, the same operation as in the case of FIG. 2 described above is performed.

On the other hand, when S1 is greater than 0 (step 102: YES) and S2 is also greater than 0 (step 103: YES), the activation control unit 28 determines the buffer accumulation amount related to the downlink buffer 21 obtained by the accumulation amount measurement unit 27. Based on the measured value Nm, a predicted activation start time T1 including a predicted value of the activation process start time of the external buffer 23 is calculated (step 104). T1 is a linear interpolation equation as shown in the following equation (3), and is calculated by dividing a value obtained by subtracting the current measured value Nm from the specified value Nw by the time change amount S1 of the measured value Nm. . In addition, about Formula (3), you may use other formulas, such as polynomial interpolation.

なお、ステップ１０４およびステップ１０５の処理順序については、これに限定されるものではなく、ステップ１０５を実行した後にステップ１０４を実行してもよく、ステップ１０４およびステップ１０５を並列的に実行してもよい。 Subsequently, the activation control unit 28, based on the estimated value Ne of the buffer accumulation amount related to the downlink buffer 21 obtained by the accumulation amount estimation unit 26, the limit start prediction time composed of the prediction value of the downlink data rate restriction start time in the OLT. T2 is calculated (step 105). T2 is a linear interpolation equation as shown in the following equation (4), and is calculated by dividing the value obtained by subtracting the current estimated value Ne from the specified value Nw by the time change amount S2 of the estimated value Ne. . In addition, about Formula (4), you may use other formulas, such as polynomial interpolation.

Note that the processing order of step 104 and step 105 is not limited to this. Step 104 may be executed after step 105 is executed, or step 104 and step 105 may be executed in parallel. Good.

Thereafter, the activation control unit 28 calculates ΔT by subtracting T1 from T2 obtained as described above (step 106), and calculates the reserve capacity ΔN from this ΔT and the speed difference Spon−Sshap. (Step 108). As shown in the following equation (5), ΔN is a speed difference between the maximum value Spon [Byte / s] of the downlink data rate communication speed and the communication speed Sshap [Byte / s] when the downlink data rate is limited. Calculated by multiplying by ΔT.

  Subsequently, the activation control unit 28 calculates the reference value Ns by subtracting the reserve capacity ΔN from the specified value (initial value) Nw (step 109), and ends the series of reference value calculation processing. As a result, the same operation as in the case of FIG. 3 described above is performed.

  In step 103, when S2 is 0 or less (step 103: NO), T2 becomes infinite, and the downlink data rate is not limited by the OLT during the activation process of the external buffer. In this case, the time during which the speed difference occurs is the activation processing period length Tw of the external buffer 32. Therefore, after ΔT is set to Tw (step 107), the process proceeds to step 108.

Next, the start control process in the start control unit 28 will be described with reference to FIG.
First, the activation control unit 28 compares the estimated value Ne of the buffer accumulation amount for the downlink buffer 21 obtained by the accumulation amount estimation unit 26 with the reference value Ns obtained by the reference value calculation process of FIG. 4 (step 120). ).
Here, when the estimated value Ne is larger than the reference value Ns (step 120: YES), an activation process start instruction for instructing activation of the external buffer 23 of the downlink buffer 21 is output (step 122), and a series of activation control processes are performed. finish.

  Further, when the estimated value Ne is equal to or less than the reference value Ns (step 120: NO), the activation control unit 28 determines the buffer accumulation amount measurement value Nm related to the downlink buffer 21 obtained by the accumulation amount measurement unit 27, as shown in FIG. The reference value Ns obtained in the reference value calculation process is compared (step 121).

Here, when the measured value Nm is larger than the reference value Ns (step 121: YES), an activation process start instruction for instructing activation of the external buffer 23 is output to the downlink buffer 21 (step 122), and a series of activation control processes are performed. finish.
Further, when the measured value Nm is equal to or less than the reference value Ns (step 121: NO), a series of activation control processes is terminated without outputting the activation process start instruction.
Note that the processing order of step 120 and step 121 is not limited to this. Step 120 may be executed after step 121 is executed, and step 120 and step 121 are executed in parallel. If any of the determination results indicates YES, the process may proceed to step 122.

  Next, the switching control process in the switching control unit 29 will be described with reference to FIG. Here, in the switching control processing in the switching control unit 29, the arrival data is transferred from the internal buffer 22 to the external buffer 23 in the downstream buffer 21 in accordance with the increase in the data accumulation amount in the buffer 21 according to the gist of the present invention. Control for switching the storage destination will be described.

First, the switching control unit 29 compares the measured value Nm of the buffer accumulation amount relating to the downlink buffer 21 obtained by the accumulation amount measurement unit 27 with a preset specified value Nw (step 130).
Here, when the measured value Nm is larger than the specified value Nw (step 130: YES), the switching control unit 29 outputs the internal output before that until the startup process in the external buffer 23 is completed (step 131: NO). By holding the state of the switching unit 24A according to the buffer switching instruction, the internal buffer is selected as the accumulation destination.

In addition, after the activation process is completed (step 131: YES), the switching control unit 29 outputs an external buffer switching instruction for selecting the external buffer 23 as the downlink data storage destination to the switching unit 24A (step 132). This switching control process ends.
When the measured value Nm is equal to or less than the specified value Nw (step 130: NO), the switching control unit 29 performs a series of switching control without switching the accumulation destination of the downlink data from the internal buffer 22 to the external buffer 23. The process ends.

[Effect of the first embodiment]
Thus, in this embodiment, in the ONU, the accumulation amount estimation unit 26 estimates the data accumulation amount in the downlink buffer 21 by monitoring the arrival data input to the downlink buffer 21, and the accumulation amount measurement unit 27, the actual amount of data stored in the downlink buffer 21 is measured, and the activation control unit 28 predicts the times T1 and T2 at which the estimated value Ne and the measured value Nm reach the specified value Nw, respectively. A reserve capacity ΔN for accumulating arrival data input to ΔT during T2 is calculated, and a reference value Ns obtained by subtracting the reserve capacity ΔN from the specified value Nw is used as an estimated value Ne or a measured value Nm. When at least one of them exceeds, start processing for changing the external buffer 23 from the use stop state to the usable state is started, and the switching control unit 29 sets the storage destination of the arrival data. When switching from the partial buffer 22 to the external buffer 23, the storage destination is switched to the second buffer when the measured value Nm exceeds the specified value Nw and the startup processing of the external buffer 23 is completed. .

  As a result, the ONU receives the PAUSE frame from the UNI, stops data transmission to the UNI, and the amount of data stored in the internal buffer 22 increases at a faster rate than the estimated value Ne in the OLT. Since the reference value Ns used for starting the start-up process of the external buffer 23 is set lower by the reserve capacity ΔN than the specified value Nw used for starting the downlink data rate restriction in the OLT, the downlink data rate restriction start in the OLT The activation process of the external buffer 23 can be started at an earlier time. Therefore, it is possible to prevent the occurrence of data loss due to the time difference ΔT between the external buffer activation processing start time T2 in the ONU and the downlink data rate restriction start time T1 in the OLT.

  In the present embodiment, the activation control unit 28 calculates the time change amount S1 of the measured value Nm and the time change amount S2 of the estimated value Ne during the predetermined time Ts, and S1 is 0. In the following cases, the specified value Nw is used as the reference value Ns, and when S1 is greater than 0 and S2 is greater than 0, the time T1 when the measured value Nm reaches the specified value Nw and the estimated value Ne are When the difference from the time T2 at which the specified value Nw is reached is the time difference ΔT, and S1 is greater than 0 and S2 is 0 or less, the activation processing period length Tw of the external buffer 23 is the time difference ΔT, and the maximum transmission in the OLT The spare capacity ΔN is calculated by multiplying the difference between the data rate Spon and the transmission data rate Sshap under the limitation of the transmission data rate at the OLT by the time difference ΔT, and only the obtained spare capacity ΔN is defined. A value subtracted from the value Nw is used as the reference value Ns.

  As a result, it is possible to calculate an optimum reference value Ns that is not excessive or deficient according to the communication characteristics of the data communication system, and to suppress the data storage capacity of the internal buffer 22 to a necessary minimum capacity.

[Second Embodiment]
Next, the data communication system 1 concerning the 2nd Embodiment of this invention is demonstrated.
In the first embodiment, the case where the startup process of the external buffer 23 is started when the estimated value Ne or the measured value Nm obtained on the ONU side exceeds the reference value Ns has been described as an example. In the present embodiment, a case will be described in which the activation process of the external buffer 23 is started even when the start of limiting the downlink data rate is notified from the OLT.

In this embodiment, when the activation detection unit 14 of the OLT detects that the estimated value Ne of the ONU buffer accumulation amount exceeds the specified value Nw, a restriction indicating the start of restriction of the downlink data rate to the ONU It has a function of explicitly notifying the ONU of the start notification.
The ONU activation control unit 28 has a function of outputting an activation process start instruction for starting the activation process of the external buffer 23 to the downlink buffer 21 in response to a restriction start notification from the OLT.

As a result, data is lost on the transmission line L, and an error occurs between the estimated value Ne of the buffer accumulation amount calculated by the accumulation amount estimation unit 26 by the ONU and the estimated buffer accumulation amount of the ONU calculated by the OLT. Even in such a case, the activation process of the external buffer 23 can be started in response to the restriction start notification from the OLT, and data loss can be prevented.
At this time, as a configuration for the OLT to notify the ONU of the start of limiting the downlink data rate, for example, there is a method using a MAC frame or a means of embedding in a part of the preamble.

[Extended embodiment]
The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Data communication system, 10 ... OLT (1st network apparatus), 11 ... Downlink buffer, 12 ... Downlink data rate control part, 13 ... Accumulation amount estimation part, 14 ... Start-up detection part, 20 ... ONU (2nd Network device), 21 ... Downstream buffer, 22 ... Internal buffer (first buffer), 23 ... External buffer (second buffer), 24A, 24B ... Switching unit, 25 ... Buffer control device, 26 ... Accumulated amount estimation unit 27 ... Accumulated amount measuring unit, 28 ... Activation control unit, 29 ... Switching control unit.

Claims (9)

A first network device that sequentially reads and transmits data temporarily stored in the transmission buffer, and when the arrival data received from the first network device via the transmission path is sequentially stored in the reception buffer, A second network device that switches the storage destination of the arrival data from the first buffer to the second buffer in the reception buffer according to an increase in the amount of data stored in the reception buffer;
The first network device is
A transmission-side accumulation amount estimation unit that estimates the data accumulation amount in the reception buffer of the second network device by monitoring the data read from the transmission buffer and transmitted to the second network device;
A time point when the estimated value indicating the data storage amount estimated by the transmission-side storage amount estimation unit exceeds a predetermined specified value is detected as a start time of starting the second buffer in the second network device. An activation detector;
Transmission data of data to be read from the transmission buffer and transmitted to the second network device over the activation process period length required for the activation process of the second buffer from the activation process start time detected by the activation detection unit A data rate control unit for limiting the rate, and
The second network device is:
An accumulation amount estimation unit that estimates the data accumulation amount in the reception buffer by monitoring the arrival data input to the reception buffer;
An accumulation amount measuring unit for measuring an actual data accumulation amount in the reception buffer;
The estimated value of the accumulated data amount estimated by the accumulated amount estimating unit and the time when the measured value of the accumulated data amount measured by the accumulated amount measuring unit reaches the specified value are predicted and input between these times. When a reserve capacity for accumulating the arrival data is calculated and at least one of the estimated value and the measured value exceeds a reference value obtained by subtracting the reserve capacity from the specified value Then, a start control unit for starting a start process for changing the second buffer from a use stop state to a usable state;
When the storage destination of the arrival data is switched from the first buffer to the second buffer, the storage destination is set to the second buffer when the measured value exceeds the specified value and the activation process is completed. A data communication system comprising: a switching control unit that switches to the buffer. The data communication system according to claim 1, wherein
The activation control unit
For each predetermined time Ts, a time change amount S1 of the measured value and a time change amount S2 of the estimated value during the Ts are calculated,
When the S1 is 0 or less, the specified value is set as the reference value,
When S1 is greater than 0 and S2 is greater than 0, the difference between time T1 when the measured value reaches the specified value and time T2 when the estimated value reaches the specified value is defined as a time difference ΔT. ,
When the S1 is greater than 0 and the S2 is 0 or less, the activation process period length Tw of the second buffer is the time difference ΔT,
By multiplying the difference between the maximum transmission data rate Spon in the first network device and the transmission data rate Sshap under the limitation of the transmission data rate in the first network device by the time difference ΔT, the reserve capacity ΔN is obtained. A data communication system, wherein a value obtained by subtracting the calculated reserve capacity ΔN from the specified value is set as the reference value. The data communication system according to claim 1 or 2,
The activation detection unit transmits a restriction start notification indicating a restriction start of the transmission data rate to the second network device when the estimated value exceeds the specified value,
The switching control unit starts the activation process for making the second buffer usable in response to reception of the restriction start notification. The data temporarily stored in the transmission buffer is sequentially read and transmitted, and is transmitted to the second network device based on the estimated value of the data accumulation amount in the reception buffer of the second network device serving as the communication partner. The data in the reception buffer is provided in the second network device that sequentially accumulates the arrival data received via the transmission path from the first network device that controls the transmission data rate of the data to be received in the reception buffer. A buffer control device that switches the destination of the arrival data from the first buffer to the second buffer in the reception buffer in accordance with an increase in the accumulation amount,
An accumulation amount estimation unit that estimates the data accumulation amount in the reception buffer by monitoring the arrival data input to the reception buffer;
An accumulation amount measuring unit for measuring an actual data accumulation amount in the reception buffer;
Predict the time when the estimated value of the data accumulation amount estimated by the accumulation amount estimation unit and the measurement value of the data accumulation amount measured by the accumulation amount measurement unit reach a predetermined specified value, and input between these times The reserve capacity for accumulating the arrival data is calculated, and at least one of the estimated value and the measured value exceeds the reference value obtained by subtracting the reserve capacity from the specified value. A start control unit for starting a start process for changing the second buffer from the use stop state to the use enable state at a time point;
When the storage destination of the arrival data is switched from the first buffer to the second buffer, the storage destination is set to the second buffer when the measured value exceeds the specified value and the activation process is completed. And a switching control unit for switching to the other buffer. The buffer control device according to claim 4, wherein
The activation control unit
For each predetermined time Ts, a time change amount S1 of the measured value and a time change amount S2 of the estimated value during the Ts are calculated,
When the S1 is 0 or less, the specified value is set as the reference value,
When S1 is greater than 0 and S2 is greater than 0, the difference between time T1 when the measured value reaches the specified value and time T2 when the estimated value reaches the specified value is defined as a time difference ΔT. ,
When S1 is greater than 0 and S2 is 0 or less, the activation process period length Tw of the second buffer is the time difference ΔT,
By multiplying the difference between the maximum transmission data rate Spon in the first network device and the transmission data rate Sshap under the limitation of the transmission data rate in the first network device by the time difference ΔT, the reserve capacity ΔN is obtained. A buffer control device characterized in that a value obtained by subtracting the calculated reserve capacity ΔN from the specified value is set as the reference value. In the buffer control device according to claim 4 or 5,
The switching control unit starts the activation process for making the second buffer usable in response to reception of a restriction start notification indicating start of restriction of the transmission data rate from the first network device. A buffer control device characterized by: The data temporarily stored in the transmission buffer is sequentially read and transmitted, and is transmitted to the second network device based on the estimated value of the data accumulation amount in the reception buffer of the second network device serving as the communication partner. Used in a second network device that sequentially accumulates arrival data received via a transmission path from a first network device that controls a transmission data rate of data to be received in a reception buffer, and stores data in the reception buffer. A buffer control method for switching the storage destination of the arrival data from the first buffer to the second buffer in the reception buffer according to an increase in amount,
An accumulation amount estimation unit that estimates the data accumulation amount in the reception buffer by monitoring the arrival data input to the reception buffer; and
An accumulation amount measuring unit for measuring an actual data accumulation amount in the reception buffer;
The activation control unit predicts a time when the estimated value of the data accumulation amount estimated in the accumulation amount estimation step and the measurement value of the data accumulation amount measured in the accumulation amount measurement step reach a predetermined specified value, A reserve capacity for accumulating the arrival data input during time is calculated, and a reference value obtained by subtracting the reserve capacity from the specified value is at least one of the estimated value and the measured value. An activation control step for starting an activation process for changing the second buffer from a use-disabled state to an available state when either of them exceeds,
When the switching control unit switches the storage destination of the arrival data from the first buffer to the second buffer, the storage value is stored when the measured value exceeds the specified value and the start-up process is completed. A switching control step of switching the destination to the second buffer. A buffer control method comprising: The buffer control method according to claim 7, wherein
The activation control step includes:
Calculating a time change amount S1 of the measurement value and a time change amount S2 of the estimated value during the predetermined time Ts;
When S1 is 0 or less, setting the specified value as the reference value;
When S1 is greater than 0 and S2 is greater than 0, the difference between time T1 when the measured value reaches the specified value and time T2 when the estimated value reaches the specified value is defined as a time difference ΔT. And steps to
When S1 is larger than 0 and S2 is 0 or less, the second buffer activation processing period length Tw is set as the time difference ΔT;
By multiplying the difference between the maximum transmission data rate Spon in the first network device and the transmission data rate Sshap under the limitation of the transmission data rate in the first network device by the time difference ΔT, the reserve capacity ΔN is obtained. And a step of setting, as the reference value, a value obtained by subtracting the calculated reserve capacity ΔN from the specified value. In the buffer control method according to claim 7 or 8,
The switching control step starts the activation process for making the second buffer usable in response to reception of a restriction start notification indicating start of restriction of the transmission data rate from the first network device. A buffer control method comprising the steps of:

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