JP4429819B2 - Band allocation method for point-to-multipoint communication system and station side device for point-to-multipoint communication system - Google Patents

Description

  In the present invention, a station-side device and a plurality of subscriber-side devices are connected to the same transmission line, and transmission from the subscriber-side device to the station-side device is time-division multiplexed, so that the station-side device to the subscriber-side device direction. In particular, the present invention relates to a point-to-multipoint communication system in which two-way transmission of a variable-length packet is performed between both devices, and more particularly to bandwidth allocation of a subscriber-side device performed by a station-side device.

  Conventionally, in a point-to-multipoint communication system, a subscriber side device (slave station device) transmits a bandwidth request signal to a station side device (station side device) to improve transmission efficiency. (For example, patent document 1). FIG. 11 is a block diagram showing a configuration of a conventional point-to-multipoint communication system. In FIG. 11, a master station device 10 that is a station side device and a slave station device 20 that is a subscriber side device are connected by the same transmission path 1. In FIG. 11, only one slave station device 20 is configured, but the other slave station devices 20 also have the same configuration.

  The configuration of the master station device 10 will be described. The master station device 10 includes a line interface function unit 11, a band control function unit 12, a separation function unit 13, a multiplexing function unit 14, and a parameter holding function unit 15. The line interface function unit 11 is connected to the transmission line 1 and transmits / receives data to / from the slave station device 20 via the transmission line 1. The separation function unit 13 is connected to the line interface function unit 11 and separates a band request signal from a signal from the slave station device 20 toward the master station device 10, that is, an uplink signal. The separated band request signal is input to the band control function unit 12 connected to the separation function unit 13. This bandwidth request signal describes the amount of data waiting to be transmitted by the slave station device 20. The bandwidth control function unit 12 schedules bandwidth allocation of the slave station device 20 based on the transmission waiting data amount. Then, an uplink transmission timing is instructed by transmitting a transmission permission signal to the slave station device 20 based on the band allocation generated in this scheduling. The transmission permission signal generated by the band control function unit 12 is passed to the multiplexing function unit 14 connected to the band control function unit 12. The multiplexing function unit 14 multiplexes the above-described transmission permission signal with a signal from the master station device 10 toward the slave station device 20, that is, a downlink signal, and the line interface function unit 11 notifies the slave station device 20 of this.

  Next, the configuration of the slave station device 20 will be described. The slave station device 20 includes a line interface function unit 21, a transmission buffer 22, a transmission control function unit 23, a multiplexing function unit 24, and a separation function unit 25. In the transmission buffer 22, user data transmitted to the master station device 10 is accumulated as an upstream signal. The transmission control function unit 23 monitors the amount of data stored in the transmission buffer 22, generates a bandwidth request signal to the master station device 20, interprets a transmission permission signal from the master station device 20, and transmits data from the transmission buffer 22. Control. The multiplexing function unit 24 multiplexes the band request signal with the uplink signal. The separation function unit 25 separates the transmission permission signal from the downlink signal. The line interface function unit 21 is connected to the transmission line 1 and transmits / receives data to / from the master station device 10 via the transmission line 1. The bandwidth request signal generated by the transmission control function unit 23 and the user data stored in the transmission buffer 22 are transmitted to the master station device 10 through the line interface function unit 21.

  FIG. 12 is a timing chart for explaining the operation of the point-to-multipoint communication system of FIG. FIG. 12 shows an example in which three slave station devices 20 are connected to one master station device 10. In the following, in the timing chart, the three slave station devices 20 are indicated as slave station # 1, slave station # 2, and slave station # 3. The master station device 10 transmits a transmission permission signal to each slave station device 20. The transmission permission signal describes a transmission permission time (grant) permitted to each slave station device 20, that is, a time at which transmission can be started and a time at which transmission should be terminated, and the slave station device 20 has designated transmission permission. You cannot send over time. The master station device 10 schedules a transmission time, a transmission frequency, a transmission order, and the like for the slave station device 20 by reflecting the traffic situation. In order to reflect the traffic situation of the slave station device 20 in the bandwidth allocation, the slave station device 20 transmits a bandwidth request signal to the master station separately from the user data. This bandwidth request signal describes the amount of data waiting to be transmitted by the slave station device 20. By using the band request signal, the master station device 10 increases the transmission time or the transmission frequency for the slave station device 20 with a large amount of data waiting for transmission, and the slave station device 20 with a small amount of data waiting for transmission. On the other hand, the transmission time is shortened or the transmission frequency is lowered, and the band is effectively utilized.

  When upstream traffic is simultaneously generated in many slave station devices 20, if the master station device 10 performs grant allocation according to the bandwidth request signal of the slave station device 20, the uplink transmission interval becomes long for the slave station device 20. Therefore, there is a problem when using a delay-sensitive application. For this reason, the master station device 10 sets the band update cycle to a constant value, and divides the time zone so as to be fair according to the traffic situation of the slave station device 20 (see, for example, Non-Patent Document 1).

  Since it is impossible to reduce the time required for the bandwidth allocation calculation to 0, a time zone for receiving only the bandwidth request signal is provided as shown in FIG. 13, and the bandwidth request signal from all the slave station devices 20 is provided in that time zone. The calculation time is ensured until the transmission permission signal is transmitted in the next cycle.

JP 2000-244527 A Ota et al. “Dynamic Bandwidth Method to Achieve Low Delay EPON”, IEICE Technical Report, NS2002-18

  When the host protocol is TCP / IP, the next data is transmitted after waiting for a response from the opposite station. Therefore, if the round trip time is large, the throughput cannot be increased. In the conventional technique, since the slave station device 20 transmits a bandwidth request signal to the master station device 10 and the master station device 10 permits transmission, a transmission waiting time of several cycles occurs as shown in FIG. . In FIG. 14, it is assumed that there is no transmission waiting data when slave station # 1 sends a band request signal in the k period, but uplink data is generated immediately after sending the band request signal. Since the slave station # 1 notifies that there is no transmission waiting data in the k period, the master station assigns a small grant to the slave station # 1. Therefore, the slave station # 1 cannot transmit the generated uplink data in the (k + 1) period. Since the slave station # 1 can notify that there is data waiting to be transmitted in the band request signal in the k + 1 cycle, the master station increases the grant assignment for the slave station # 1 in the bandwidth assignment in the k + 2 cycle. That is, the slave station # 1 has a waiting time several times longer than the bandwidth update period before obtaining a grant allocation suitable for the traffic.

  As a means for reducing the transmission waiting time, there is a method in which the master station device 10 assigns a certain grant without referring to the transmission waiting data amount of the slave station device 20. However, as shown in FIG. 15, when a variable-length packet such as an ether frame is multiplexed, the master station device 10 cannot know the delimitation of the ether frame in the transmission buffer of the slave station device 20, so that the grant length Cannot be matched with the boundary of the Ethernet frame, and the band use efficiency is lowered.

  Although it is possible to reduce the transmission waiting time by shortening the bandwidth update cycle, the bandwidth update cycle is less than the round trip time between the master station device 10 and the slave station device 20 farthest from the master station device 10. Cannot be reduced. Moreover, there is a demerit that if the bandwidth update period is reduced, the bandwidth utilization efficiency decreases. This is because, as shown in FIG. 16, the upstream signal of each slave station device 20 includes a burst overhead for correctly receiving the signal by the master station device 10. That is, if the band update period is short, the ratio of burst overhead in the uplink signal is relatively large, and the ratios of the band request signal and transmission permission signal not including user data are also relatively large. Therefore, in order to increase the transmission efficiency, a larger value for the band update period is more advantageous.

  As described above, the conventional technology has an unresolved problem that the bandwidth use efficiency decreases when the transmission wait time is shortened, and the transmission wait time becomes large when the bandwidth use efficiency is increased. ing.

  The present invention has been made in view of the above-described problems of the prior art, and provides a bandwidth allocation method for a point-to-multipoint communication system capable of realizing both a short transmission waiting time and a high bandwidth utilization efficiency, and It is an object of the present invention to obtain a station side device band allocation method for a point-to-multipoint communication system.

  The bandwidth allocation method of this point-to-multipoint communication system connects station side devices and multiple subscriber side devices on the same transmission line, and time-division transmission from subscriber side devices to station side devices. In a point-to-multipoint communication system that performs multi-directional transmission of variable-length packets using broadcast transmission from the station side device to the subscriber side device, the subscriber side device requests the bandwidth for the amount of data waiting to be transmitted. The station side device is notified by a signal, the station side device schedules the bandwidth allocation of the subscriber side device based on the amount of data waiting for transmission, and transmits a transmission permission signal to the subscriber side device based on the bandwidth allocation. A bandwidth allocation method for instructing uplink transmission timing, wherein the station side device allocates the data amount that can be allocated in one bandwidth update cycle and the transmission waiting data notified from all the subscriber side devices. When the ratio of the total amount of data waiting to be transmitted notified from all subscriber side devices to the amount of data that can be allocated in one bandwidth update period is less than the threshold value, the load is reduced. If the sum of the data waiting to be transmitted notified from all the subscriber side devices is larger than the data amount that can be allocated in one bandwidth update cycle, the overload state is set. In the load state, 1% is assigned in the overload state so that the transmission permission time equal to the data amount required by the subscriber side apparatus is assigned in the high load state so that the total amount of data allocated per cycle becomes the lower limit value. Bandwidth allocation is performed so that the total allocated data amount per period becomes an upper limit value.

  In the bandwidth allocation method of the point-to-multipoint communication system according to the present invention, a transmission permission time equal to the data amount requested by the subscriber side apparatus is allocated based on the transmission waiting data amount notified from the subscriber side apparatus. In addition, since it is selected whether the total allocated data amount per cycle becomes the lower limit value or the upper limit value, more optimal bandwidth allocation can be performed. Both a short transmission waiting time and high bandwidth utilization efficiency can be realized.

  Embodiments of a band allocation method for a point-to-multipoint communication system and a station-side apparatus of the point-to-multipoint communication system according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a point-to-multipoint communication system according to the present invention. In FIG. 1, a master station device 10 that is a station side device and a slave station device 20 that is a subscriber side device are connected by the same transmission path 1. In FIG. 1, the configuration of only one slave station device 20 is shown, but the other slave station devices 20 also have the same configuration.

  The configuration of the master station device 10 will be described. The master station device 10 includes a line interface function unit 11, a band control function unit 12, a separation function unit 13, a multiplexing function unit 14, and a parameter holding function unit 15. The line interface function unit 11 is connected to the transmission line 1 and transmits / receives data to / from the slave station device 20 via the transmission line 1. The separation function unit 13 is connected to the line interface function unit 11 and separates a band request signal from a signal from the slave station device 20 toward the master station device 10, that is, an uplink signal. The separated band request signal is input to the band control function unit 12 connected to the separation function unit 13. This bandwidth request signal describes the amount of data waiting to be transmitted by the slave station device 20. The bandwidth control function unit 12 schedules bandwidth allocation of the slave station device 20 based on the transmission waiting data amount. Then, the uplink transmission timing is instructed by transmitting a transmission permission signal to the slave station apparatus 20 based on the band allocation generated by the scheduling. A parameter holding function unit 15 is connected to the band control function unit 12. The parameter holding function unit 15 holds parameters necessary for bandwidth control. The parameters held in the parameter holding function unit 15 can be input from the outside of the apparatus. The transmission permission signal generated by the band control function unit 12 is passed to the multiplexing function unit 14 connected to the band control function unit 12. The multiplexing function unit 14 multiplexes the above-described transmission permission signal with a signal from the master station device 10 toward the slave station device 20, that is, a downlink signal, and the line interface function unit 11 notifies the slave station device 20 of this.

  Next, the configuration of the slave station device 20 will be described. The slave station device 20 includes a line interface function unit 21, a transmission buffer 22, a transmission control function unit 23, a multiplexing function unit 24, and a separation function unit 25. In the transmission buffer 22, user data transmitted to the master station device 10 is accumulated as an upstream signal. The transmission control function unit 23 monitors the amount of data stored in the transmission buffer 22, generates a bandwidth request signal to the master station device 10, interprets a transmission permission signal from the master station device 10, and transmits data from the transmission buffer 22. Take control. The multiplexing function unit 24 multiplexes the band request signal with the uplink signal. The separation function unit 25 separates the transmission permission signal from the downlink signal. The line interface function unit 21 is connected to the transmission line 1 and transmits / receives data to / from the master station device 10 via the transmission line 1. The bandwidth request signal generated by the transmission control function unit 23 and the user data stored in the transmission buffer 22 are transmitted to the master station device 10 through the line interface function unit 21.

[Three states of data waiting to be sent]
Prior to the description of the bandwidth allocation operation performed by the bandwidth control function unit 12, three states of the transmission waiting data amount recognized by the present embodiment will be described. Based on the amount of data waiting for transmission notified from each slave station device 20 in the system, the bandwidth control function unit 12 regards the state of uplink data as the following three states and manages this.
(A) Low load state: A state in which the ratio of the sum of the transmission waiting data amounts of all the slave station devices 20 to the data amount that can be allocated in one bandwidth update cycle is less than the threshold value.
(B) High load state: A state in which the ratio of the sum of the transmission waiting data amounts of all the slave station devices 20 to the data amount that can be allocated in one bandwidth update cycle is equal to or greater than a threshold.
(C) Overload state: A state in which the sum of the transmission waiting data amounts of all the slave station devices 20 is larger than the data amount that can be allocated in one bandwidth update cycle.

The amount of data that can be allocated in one bandwidth update cycle, that is, the total allocated data amount per cycle has an upper limit value and a lower limit value, and each upper limit value is BW_cycle_max
Lower limit: BW_cycle_min
It is said that. BW_cycle_max and BW_cycle_min satisfy the following relationship.
BW_cycle_max ≧ BW_cycle_min (Formula 1)

  The master station device 10 stores in the parameter holding function unit 15 set values such as the threshold value Th for determining the low load state and the high load state described above, and the weight W (i) when allocating the bandwidth to each slave station device. is doing. These set values can be input from the outside of the apparatus as described above.

[Determination of status]
Next, the bandwidth allocation operation performed by the bandwidth control function unit 12 of the master station device 10 will be described. First, the state determination operation will be described with reference to the flowchart of FIG. The band control function unit 12 performs the operation of the flowchart of FIG. 2 for each period of the band update period. First, at step S1, the loop is repeated for the number of all slave station devices, thereby extracting the transmission waiting data amount BW_req (i) from the band request signal from all the slave station devices. Next, in step S2, the load factor P, which is the ratio of the total transmission waiting data amount of all the slave station devices 20 to the data amount per cycle, is calculated by the following equation.
P = Σ {BW_req (i)} / BW_cycle_max (Formula 2)
Next, in step S3, the load factor P is compared with the threshold value Th in order to determine the load state. If it is determined in step S3 that the load factor P is smaller than the threshold value Th, the load factor P is recognized as being in a low load state, and the process proceeds to the low load mode grant allocation processing step S4. If P is greater than or equal to the threshold Th, the process proceeds to step S5. In step S5, it is determined whether or not the load factor is 1 or less, that is, whether or not the total amount of data waiting for transmission exceeds the total allocated data amount per cycle. If true in step S5, it is recognized that the vehicle is in a high load state, and the flow proceeds to high load mode grant allocation processing step S6. If it is determined to be false in step S6, it recognizes that it is in an overload state, and proceeds to overload mode grant allocation processing step S7. Each processing of the low load mode grant allocation processing step S4, the high load mode grant allocation processing step S6, and the overload mode grant allocation processing step S7 will be described later.

  In step S8, the grant calculated in any of the low load mode grant allocation processing step S4, the high load mode grant allocation processing step S6, and the overload mode grant allocation processing step S7 is repeated by repeating the loop for the number of all slave station devices. Is multiplexed with the transmission permission signal and transmitted to each slave station device. When step S8 is completed, the process returns to step S1 and the next cycle is performed. Thereafter, the above process is repeated.

[Bandwidth allocation processing under low load]
Processing in the low load mode grant allocation processing step S4 will be described. In a low load state, the total allocation data amount per cycle is set to the lower limit value BW_cycle_min in order to shorten the time until grant allocation for the slave station apparatus in which the uplink data is generated. There are various variations on the ratio of the total allocated data amount per cycle to the slave station apparatus. In this embodiment, in order to increase the grant allocation amount for the slave station apparatus in which uplink data is generated, the bandwidth allocation is proportional to the transmission waiting data amount BW_req (i). In this case, the allocated bandwidth BW (i) for each slave station device is determined by the following equation.
BW (i) = BW_cycle_min × BW_req (i) / Σ {BW_req (i)} (Formula 3)

  The details of the processing operation of the low load mode grant allocation processing step S4 are shown in the flowchart of FIG. In FIG. 3, first, in step S10, the process of the above equation 3 is repeated for the number of slave station devices. Next, in step S11, the value calculated in step S10 is set as a grant for user data by repeating the loop for the number of all slave station devices. Further, in step S102, the loop corresponding to the number of all slave station devices is repeated to set a grant corresponding to the packet length of the bandwidth request signal as the grant for the bandwidth request signal. A specific example is shown in FIG. In FIG. 4, as an example, BW_cycle_max = 10000 bytes, BW_cycle_min = 2000 bytes, and threshold Th = 0.5. In the k-th cycle, the slave station device # 1 notifies the transmission waiting data amount of 300 bytes, the slave station device # 2 notifies the transmission waiting data amount of 200 bytes, and the slave station device # 3 notifies the transmission waiting data amount of zero. Since the total amount of data waiting to be transmitted from slave station apparatuses # 1 to # 3 is 500 bytes, the load factor is 0.05 according to Equation 2, and the low load mode is set. The bandwidth allocated to each slave station device in the (k + 1) -th cycle is 1200 bytes for slave station device # 1, 800 bytes for slave station device # 2, and 0 bytes for slave station device # 3 according to Equation 3. The bandwidth update at this time is performed by adding a transmission permission signal reception time zone to the time required for transferring 2000 bytes.

[Bandwidth allocation under high load]
Processing in the high load mode grant allocation processing step S6 will be described. In a high load state, since there are many slave station devices that request a bandwidth, it is necessary to increase the bandwidth utilization efficiency, and the gap between the uplink data packets and the grant length are matched to reduce the discarded bandwidth. This is realized by assigning a grant equal to the amount of data required by the slave station device. Therefore, the allocated bandwidth BW (i) for each slave station device is determined by the following equation.
BW (i) = BW_req (i) (Formula 4)

  Details of the high load mode grant allocation processing step S6 are shown in the flowchart of FIG. In FIG. 5, first, in step S20, the processing of the above equation 4 is repeated for the number of slave station devices. Next, in step S21, the value calculated in step S20 is set as a grant for user data by repeating the loop for the number of all slave station devices. In step S22, a grant corresponding to the packet length of the bandwidth request signal is set as the grant for the bandwidth request signal. A specific example is shown in FIG. In FIG. 6, as an example, BW_cycle_max = 10000 bytes, BW_cycle_min = 2000 bytes, and threshold value Th = 0.5. In the k-th cycle, the slave station device # 1 notifies the transmission waiting data amount of 4000 bytes, the slave station device # 2 notifies the transmission waiting data amount of 3000 bytes, and the slave station device # 3 notifies the transmission waiting data amount of 1000 bytes. Since the total amount of data waiting to be transmitted from the slave station devices # 1 to # 3 is 8000 bytes, the load factor becomes 0.8 from Equation 2 and the high load mode is set. The bandwidth allocated to each slave station device in the (k + 1) -th cycle is 4000 bytes for slave station device # 1, 3000 bytes for slave station device # 2, and 1000 bytes for slave station device # 3 according to Equation 4. The bandwidth update at this time is performed by adding the transmission permission signal reception time zone to the time required to transfer 8000 bytes.

[Bandwidth allocation processing under overload]
The process in overload mode grant allocation process step S7 is demonstrated. In an overload state, since there are many slave station devices that request bandwidth, it is necessary to improve bandwidth utilization efficiency, and the total allocated data amount per cycle is set to the upper limit value BW_cycle_max. Since the sum of the bandwidth requests of all the slave station devices exceeds the total allocated data amount per cycle, the bandwidth as requested by all the slave station devices is not allocated, and the allocated bandwidth is set to be fair to the slave station devices. It is necessary to calculate. In the present embodiment, weighting is performed with a parameter W (i) serving as a charge reference, and the allocated bandwidth BW (i) for each slave station device is determined by the following equation.
BW (i) = BW_cycle_max × W (i) / Σ {W (i)} (Formula 5)
As an example, when the parameter W (i) serving as a fee standard is the minimum guaranteed bandwidth BW_min (i) of each slave station device, (Formula 5) is as follows.
BW (i) = BW_cycle_max × BW_min (i) / Σ {BW_min (i)} (Formula 6)

  Details of the overload mode grant allocation processing step S6 are shown in the flowchart of FIG. In FIG. 7, first, in step S30, the processing of the above equation 4 is repeated for the number of slave station devices. Next, in step S31, the value calculated in step S30 is set as a grant for user data by repeating the loop for the number of all slave station devices. In step S32, a grant corresponding to the packet length of the bandwidth request signal is set as the grant for the bandwidth request signal. A specific example is shown in FIG. As an example, BW_cycle_max = 10000 bytes, BW_cycle_min = 2000 bytes, and threshold Th = 0.5. In the K-th cycle, the slave station device # 1 notifies the transmission waiting data amount of 5000 bytes, the slave station device # 2 notifies the transmission waiting data amount of 5000 bytes, and the slave station device # 3 notifies the transmission waiting data amount of 5000 bytes. Since the total amount of data waiting to be transmitted from the slave station devices # 1 to # 3 is 15000 bytes, the load factor is 1.5 according to Equation 2 and the overload mode is set. Here, it is assumed that the minimum guaranteed bandwidth BW_min (i) of each slave station device is, for example, 20 Mbps for slave station device # 1, 10 Mbps for slave station device # 2, and 10 Mbps for slave station device # 3. In this case, the bandwidth allocated to each slave station device in the (K + 1) -th cycle is 5000 bytes for slave station device # 1, 2500 bytes for slave station device # 2, and 2500 bytes for slave station device # 3 according to Equation 5. The bandwidth update at this time is performed by adding the transmission permission signal reception time zone to the time required to transfer 10,000 bytes.

  As described above, the bandwidth allocation method of delay priority or transmission efficiency priority is selected according to the uplink congestion state. Since the bandwidth is updated in a short cycle when the load is low, the time that user data stays in the upstream buffer of the slave station device is short, the round trip time can be shortened, and high throughput can be extracted even in TCP / IP. It becomes. In other words, it is possible to transmit traffic that fully utilizes a vacant upstream band in the upstream direction. In a high load state, a grant equal to the amount of data is assigned as notified by the slave station device, so that the packet break and grant length are equal, and high transmission efficiency can be derived. That is, when the bandwidth requirement is large as a whole, high transmission efficiency can be realized and the bandwidth per slave station device can be increased. Even in an overload state, the next grant allocation pattern is changed at the upper limit value of the bandwidth update period, so that the worst value of the round trip time can be guaranteed.

Embodiment 2. FIG.
In Embodiment 1 described above, no particular mention was made regarding the transmission permission time between the band request signal and the user data. However, in the present embodiment, the band request signal and the user data are transmitted only in a low load state. An example in which the permitted time is not distinguished is shown. That is, in the present embodiment, the transmission permission time is distinguished between the band request signal and the user data in the high load state and the overload state, but is not distinguished in the low load state. In a low load state, a grant that is substantially larger than the value required by the slave station device is allocated. Therefore, the bandwidth request signals of all the slave station devices are intensively collected in the time zone for receiving the bandwidth request signal to obtain the bandwidth request. This is based on the fact that it is not necessary to assign a strict bandwidth to the value.

  FIG. 9 is a flowchart showing the band allocation operation in the present embodiment. In FIG. 9, first, in step S41, the fixed bandwidth BW_fix (i) and the requested bandwidth BW_req (i) are compared. Here, the fixed band BW_fix (i) is a value indicating the fixed band to be allocated regardless of the band request, and is assumed to be held in the parameter holding function unit 15 in advance. If it is determined in step S41 that BW_req (i) is equal to or less than BW_fix (i), the process proceeds to step S42, and BW_req (i) is forcibly made equal to BW_fix (i). On the other hand, if it is determined in step S41 that BW_req (i) is greater than BW_fix (i), step S42 is skipped. And step S41 to step S42 is performed with respect to all the slave station apparatuses.

  Steps S43 to S44 are the same as steps S11 and S12 in FIG. A specific example is shown in FIG. As an example, BW_cycle_max = 10000 bytes, BW_cycle_min = 2000 bytes, and threshold Th = 0.5. Also, BW_fix (i) is 20 bytes for the slave station devices # 1, # 2, and # 3. In the k-th cycle, the slave station device # 1 notifies the transmission waiting data amount of 100 bytes, the slave station device # 2 notifies the transmission waiting data amount of 80 bytes, and the slave station device # 3 notifies the transmission waiting data amount of zero. Since the total amount of data waiting to be transmitted from slave station apparatuses # 1 to # 3 is 180 bytes, the load factor is 0.018 from Equation 2 and the low load mode is set. BW_req (i) is converted into BW_req (1) = 100, BW_req (2) = 80, and BW_req (3) = 20 from step S41 to step S42 in FIG. The bandwidth allocated to each slave station device in the (k + 1) -th cycle is 1000 bytes for slave station device # 1, 800 bytes for slave station device # 2, and 200 bytes for slave station device # 3 according to Equation 3. The bandwidth update at this time is performed in the time required to transfer 2000 bytes.

  As described above, since the band request signal and the user data grant are not separated in the low load state, the burst overhead of the band request signal grant can be reduced, and the transmission efficiency can be increased. In addition, since the bandwidth is allocated even if the bandwidth request is 0, the upstream signal generated after transmitting the bandwidth request signal can be transmitted upstream without waiting time.

  It is useful when applied to point-to-multipoint communication systems to which many subscriber devices are connected, and is particularly applicable to point-to-multipoint communication systems that require efficient and high-speed services. It is useful.

It is a block diagram which shows the structure of Embodiment 1 of the point-to-multipoint communication system which concerns on this invention. It is a flowchart which shows operation | movement of a main | base station apparatus (station side apparatus). It is a flowchart which shows the detail of operation | movement of a low load mode grant allocation process. It is a timing chart which shows the specific example of the band allocation process in a low load state. It is a flowchart which shows the detail of operation | movement of a high load mode grant allocation process. It is a timing chart which shows the specific example of the band allocation process in a high load state. It is a flowchart which shows the detail of operation | movement of an overload mode grant allocation process. It is a timing chart which shows the specific example of the band allocation process in an overload state. It is a flowchart which shows the operation | movement of the band allocation process of Embodiment 2 of the point-to-multipoint communication system which concerns on this invention. 10 is a timing chart illustrating a specific example of bandwidth allocation processing according to the second embodiment. It is a block diagram which shows the structure of the conventional communication system. 12 is a timing chart showing the operation of the communication system of FIG. 11. It is a timing chart which shows the operation | movement which provided the time slot | zone which receives only the band request signal of the conventional communication system. It is a timing chart which shows a mode that the transmission waiting time for several cycles of the conventional communication system generate | occur | produces. 6 is a timing chart showing how bandwidth utilization efficiency decreases when a variable-length packet such as an Ethernet frame is multiplexed in a conventional communication system. It is a timing chart which shows a mode that band utilization efficiency falls in the conventional communication system when a zone | band update period is made small.

Explanation of symbols

10 Master station device (station side device)
11 Line Interface Function Unit 12 Band Control Function Unit 13 Separation Function Unit 14 Multiplex Function Unit 15 Parameter Holding Function Unit 20 Slave Station Device (Subscriber Side Device)
21 Line Interface Function Unit 22 Transmission Buffer 23 Transmission Control Function Unit 24 Multiplex Function Unit 25 Separation Function Unit

Claims (8)

A station-side device and a plurality of subscriber-side devices are connected by the same transmission line, and transmission from the subscriber-side device to the station-side device is time-division multiplexed, and the station-side device is connected to the subscriber-side device. In a point-to-multipoint communication system that performs bidirectional transmission of variable-length packets by broadcasting direction transmission,
The subscriber side device notifies the station side device of the amount of data waiting for transmission to the station side device by a bandwidth request signal, and the station side device schedules bandwidth allocation of the subscriber side device based on the amount of data waiting for transmission, A bandwidth allocation method for instructing uplink transmission timing by transmitting a transmission permission signal to the subscriber side device based on the bandwidth allocation,
The station side device compares the amount of data that can be allocated in one bandwidth update cycle with the sum of the transmission waiting data notified from all the subscriber side devices,
When the ratio of the total amount of data waiting for transmission notified from all the subscriber side devices to the amount of data that can be allocated in one bandwidth update cycle is less than the threshold, the load is low, and when the ratio is above the threshold, the load is high And an overload state when the total amount of data waiting to be transmitted notified from all the subscriber side devices is larger than the amount of data that can be allocated in one bandwidth update cycle,
In the low load state, the overload is performed so that a transmission permission time equal to the data amount required by the subscriber side apparatus is allocated in the high load state so that the total allocated data amount per cycle becomes a lower limit value. In the state, the bandwidth is allocated so that the total allocated data amount per cycle becomes the upper limit value ,
The station side device receives the bandwidth request signal and user data without distinguishing the transmission permission time in the low load state, and receives the distinction in the high load state and the overload state. A bandwidth allocation method for a point-to-multipoint communication system. The comparison between the amount of data that can be allocated in one bandwidth update cycle performed by the station side device and the sum of the transmission waiting data notified from all the subscriber side devices is performed every cycle. The band allocation method of the point-to-multipoint communication system according to claim 1 . In the low load state, the station side device sets the lower limit value to BW_cycle_min and the transmission waiting data amount of each subscriber side device to BW_req (i), and assigns the allocated bandwidth BW (i) to each subscriber side device. Calculate by the following formula
BW (i) = BW_cycle_min × BW_req (i) / Σ {BW_req (i)}
The band allocation method of the point-to-multipoint communication system according to claim 1 or 2 , In the overload state, the station side device assigns the upper limit value to BW_cycle_max and assigns a bandwidth to each subscriber side device as W (i). )
BW (i) = BW_cycle_max × W (i) / Σ {W (i)}
The band allocation method of the point-to-multipoint communication system according to any one of claims 1 to 3 . It is connected to a plurality of subscriber-side devices through the same transmission path, the transmission from the subscriber-side device to the own device is time-division multiplexing, and the transmission from the own device to the subscriber-side device is broadcast as the subscription. A station-side device of a point-to-multipoint communication system that performs bidirectional communication of variable-length packets to a user-side device,
A line interface function unit that is connected to the transmission line and receives a transmission waiting data amount from the subscriber side device notified by a bandwidth request signal;
A bandwidth control function unit that schedules bandwidth allocation of the subscriber side device based on the amount of data waiting to be transmitted, and that indicates an uplink transmission timing by transmitting a transmission permission signal to the subscriber side device based on the bandwidth allocation And
The bandwidth control function unit compares the amount of data that can be allocated in one bandwidth update period with the total amount of data waiting to be transmitted notified from all the subscriber side devices,
When the ratio of the total amount of data waiting to be transmitted notified from all the subscriber side devices to the amount of data that can be allocated in one bandwidth update cycle is less than the threshold, the load is set to a low load state. And an overload state when the total amount of data waiting to be transmitted notified from all the subscriber side devices is larger than the amount of data that can be allocated in one bandwidth update cycle,
In the low load state, the excessive allocation time is allocated so as to allocate a transmission permission time equal to the data amount required by the subscriber side device in the high load state so that the total allocated data amount per cycle becomes a lower limit value. In the load state, bandwidth is allocated so that the total allocated data amount per cycle becomes the upper limit value .
The bandwidth control function unit receives the bandwidth request signal and user data without distinguishing the transmission permission time in the low load state, and distinguishes and receives in the high load state and the overload state. A station-side device of a point-to-multipoint communication system. The bandwidth control function unit compares the amount of data that can be allocated in one bandwidth update cycle with the sum of the amount of data waiting to be transmitted notified from all the subscriber side devices, every cycle. The station side apparatus of the point-to-multipoint communication system according to claim 5 . The bandwidth control function unit, in the low load state, when the lower limit value is BW_cycle_min and the transmission waiting data amount of each subscriber side device is BW_req (i), the allocated bandwidth BW (i) for each subscriber side device Is obtained by the following formula:
BW (i) = BW_cycle_min × BW_req (i) / Σ {BW_req (i)}
The station side apparatus of the point-to-multipoint communication system according to claim 5 or 6 . In the overload state, the bandwidth control function unit assigns the upper limit value to BW_cycle_max and assigns the bandwidth to each subscriber side device as W (i), and assigns the bandwidth BW ( i) is obtained by the following equation.
BW (i) = BW_cycle_max × W (i) / Σ {W (i)}
The station side apparatus of the point-to-multipoint communication system according to any one of claims 5 to 7 .

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