JP2004040666A - Node device, terminal equipment, program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology for assigning a communication band to a multicast communication flow without waste while securing profits of a receiver to take part in a multicast group. <P>SOLUTION: When transmitting a packet addressed to the multicast group from a node device 60 to a network switch 30, the node device 60 acquires the number of receiving apparatuses 70 which take part in each multicast group for each radio access point device 40 and as the number is greater, the wider communication band is assigned to the transmission of the packet addressed to the multicast group. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for effectively using a communication band.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, most of communication performed on a communication network such as the Internet uses a personal computer (hereinafter, referred to as “PC”) or a workstation (hereinafter, referred to as “PC”) used by a data sender to transmit the data. WS ") and a terminal device such as a PC, a mobile phone, or a PDA (Personal Digital Assistance) used by a receiver of the data to receive the data. (Hereinafter, referred to as a “receiving device”) in a communication mode of performing one-to-one communication (hereinafter, such a communication mode is referred to as “unicast”). As another communication mode of the unicast, there is a communication mode in which a transmitting apparatus and a receiving apparatus perform one-to-many or many-to-many communication (hereinafter, such a communication mode is referred to as “multicast”).
[0003]
As an example of multicast, IP multicast that realizes multicast using IP (Internet Protocol) widely used in the Internet and the like as a communication protocol of a network layer is widely known. In IP multicast, a multicast group is configured by assigning a multicast IP address to a group of receiving apparatuses that receive the same data. The IP address assigned to this multicast group is unique to the group. A receiving device that receives data to be multicast to a multicast group first has a node device (for example, a router, etc.) that manages the communication network to which the receiving device belongs, and a receiving device belonging to the multicast group in the communication network. Information indicating the presence is stored. That is, the receiving device first joins the multicast group. Then, when data transmitted from the transmitting device to the IP address of the multicast group is routed to the node device, the node device transmits the data to the receiving device participating in the multicast group under its own device. Multicast is realized by copying the required number of data and transmitting the data to each receiving device.
[0004]
When the transmitting device actually transmits data, the transmitting device divides the data into a plurality of data blocks (hereinafter, referred to as “packets”) and transmits the data blocks. Each of the plurality of packets includes data (hereinafter, referred to as “divided data”) divided into data sizes of a communication unit and information indicating a destination of the packet (for example, an IP address of a receiving device). Have been. On the other hand, when the receiving device receives the plurality of packets, the receiving device obtains the divided data included in each of the plurality of packets, and assembles the plurality of divided data, thereby transmitting the divided data from the transmitting device. Get the data that has been. Also in the case of transmitting data by the above-mentioned multicast, data transmission / reception and copying are performed in packet units.
[0005]
The above-described multicast can be realized not only in a wired communication network but also in a wireless communication network such as a wireless LAN (Local Area Network) defined by IEEE (Institute of Electrical and Electronic Engineers) 802.11b. In a wireless LAN, communication waves transmitted from a wireless access point device can be received by all receiving devices connected to the wireless access point device. Therefore, when transmitting a packet addressed to a multicast group from a wireless access point device, In such a case, the wireless access point device does not need to duplicate packets as many as the number of receiving devices and transmit the packets, and multicast can be realized by transmitting one packet to the multicast group.
[0006]
As described above, when the same packet is transmitted to a plurality of receiving devices by multicast, the transmitting device only needs to transmit the packet once to a multicast group to which the plurality of receiving devices belong. The load on the transmitting device does not increase even if the number of the devices increases. Further, since the transmitting device transmits only one packet to the node device for one multicast group, even if the number of receiving devices increases, the communication band required for transmitting the packet does not increase. On the other hand, if the same data is transmitted to a plurality of receiving devices by unicast, the transmitting device must transmit the same data to each receiving device, which is proportional to the increase in the number of receiving devices. As a result, the load on the transmission device increases. Also, between the transmitting device and the node device, since the number of packets transmitted by the transmitting device increases in proportion to the increase in the number of receiving devices, it is necessary to transmit packets in proportion to the increase in the number of receiving devices. Communication bandwidth is widened.
In summary, when the same packet is transmitted to a plurality of receiving devices, the use of multicast reduces the load on the transmitting device compared to the case of using unicast, and the communication band can be used effectively. There are advantages. In a wireless LAN, the wireless access point device that transmits data to a multicast group does not need to duplicate and transmit packets as many as the number of receiving devices participating in the multicast group. become.
[0007]
[Problems to be solved by the invention]
In the case of transmitting the same packet to a plurality of receiving devices, unicast is widely used in the past, though multicast is more advantageous than unicast. The reasons for this are that the advantages of multicasting described above are advantages only for the data sender and the carrier that manages the communication network, and that there is no advantage for the receiver to receive the multicast data. No. The following explains why there is no advantage to using multicast for the receiver.
[0008]
As described above, the data transmitted from the transmitting device is divided into a plurality of packets and transmitted to the receiving device. Generally, a flow of a packet from a transmitting device to a receiving device in a communication network (hereinafter, a flow of a packet having the same destination is referred to as a “communication flow”, and a destination of a packet constituting the communication flow is referred to as a “destination of a communication flow”. ), A sufficient communication speed is not secured and a packet does not reach the receiving device (hereinafter, referred to as “packet loss”). When such a packet loss occurs, the receiving device cannot correctly assemble the data transmitted from the transmitting device. In the case of unicast, even if a packet is lost, only one receiver is affected.In the case of multicast, when a packet is lost, multiple recipients participating in the multicast group are affected. Are all affected. Accordingly, a communication flow destined for a multicast group in which a plurality of receiving devices participate (hereinafter, referred to as a “multicast communication flow”) includes a communication flow destined for a single receiving device (hereinafter, “unicast communication flow”). A communication band wider than “communication flow”) should be allocated.
[0009]
However, when a conventional node device allocates a communication band to a communication flow in a communication network managed by itself (hereinafter, such a communication network is referred to as a “local network”), the communication flow is a multicast communication flow. Or the unicast communication flow, the communication band having the same width is allocated. Therefore, for the receiver, there is no difference between the case of receiving the unicast data and the case of receiving the multicast data, and there is no advantage of actively using the multicast. In addition, since the same bandwidth is allocated to the unicast communication flow and the multicast communication flow, packet loss occurs with the same probability in both the unicast communication flow and the multicast communication flow, and the packet is sent to the multicast group. There is a problem that the greater the number of participating receivers, the greater the number of recipients affected by the packet loss.
[0010]
To solve this problem, when a node device allocates a communication band to a multicast communication flow in a local network, a width proportional to the number of receiving devices participating in a multicast group that is a destination of the multicast communication flow is used. It has been proposed to allocate a communication band of.
[0011]
In order to allow the node device to allocate a communication band having a width proportional to the number of receiving devices participating in each multicast group to each multicast communication flow, for example, the node device can be allocated in the local network. The maximum value of the communication band (hereinafter, referred to as a “maximum communication band”) is stored in advance, and the node device obtains the number of receiving devices participating in each multicast group in the local network. It is assumed that a communication band obtained by dividing the maximum communication band by a width proportional to the number of receiving devices participating in each multicast group is assigned to each multicast communication flow. In an actual communication network, a plurality of small subnetworks are included in one local network, and a node device (hereinafter, referred to as a “lower node device”) that manages the subnetwork is installed in each subnetwork. It is often done. Even in such a network form, each lower node device acquires the number of receiving devices participating in the multicast group in the subnetwork, and notifies the acquired number of receiving devices to the upper node device, The upper node device can obtain the number of receiving devices participating in each multicast group, and can allocate a communication band having a width proportional to the number of receiving devices participating in the multicast group to each multicast communication flow. it can. That is, a node device (hereinafter, referred to as an “edge node device”) that is disposed closest to the receiving device and directly manages the receiving device accurately obtains the number of receiving devices that participate in each multicast group. If this can be done, it becomes possible for all the node devices connected to the transmitting device to grasp the number of receiving devices participating in each multicast group under its own device.
[0012]
A multicast router is generally known as a node device having a special function for ascertaining that there is a receiving device participating in a multicast group in a local network. The multicast router realizes the above function by performing an operation in conformity with the Internet Group Management Protocol (IGMP) standardized by the Internet Engineering Task Force (IETF). More specifically, the multicast router transmits IGMP-Query to a receiving device in the local network. After receiving the IGMP-Query, the receiving apparatus waits for a random time and then transmits the IGMP-Report to the IP address of the multicast group in which the receiving apparatus has joined. By receiving the IGMP-Report, the multicast router can know that there is at least one receiving device participating in the multicast group in the local network, and transmit a packet addressed to the multicast group into the local network. . The reason why the receiving device waits for a random time is to prevent itself from transmitting IGMP-Report when another receiving device has already transmitted IGMP-Report. With this mechanism, the number of IGMP-Reports can be suppressed even if the number of receiving devices becomes very large. As described above, the multicast router that operates in accordance with the IGMP can determine whether or not there is a receiver participating in the multicast group in the local network. You cannot get the exact number of.
[0013]
An ECMP (Express Count Management Protocol) has been proposed as a technique for causing a node device to acquire the number of receiving devices participating in a multicast group for each multicast group in a local network. A node device that performs an operation conforming to the ECMP periodically transmits an inquiry packet for inquiring about the number of receiving devices to a multicast group to which the own device is transmitting a packet. When the receiving device that has joined the multicast group receives this inquiry packet, the receiving device transmits a response packet notifying that it has joined the multicast group to the node device. The node device that performs the operation conforming to the ECMP receives this response packet, and can acquire the number of receiving devices participating in each multicast group by counting the number of received response packets. Note that in ECMP, by allowing each receiving device to transmit a response packet to which information indicating that the receiving device is a legitimate receiving device, the node device checks whether the receiving device participating in the multicast group is a legitimate receiving device. It can also be determined whether or not.
[0014]
Hereinafter, a flow of an operation in which a node device that performs an operation conforming to ECMP allocates a communication band having a width proportional to the number of receiving devices participating in a multicast group to each multicast communication flow will be described with reference to FIG. . The communication system shown in FIG. 1 includes transmitting devices 10A, 10B, and 10C, the Internet 100, a node device 20, a network switch 30, wireless access point devices 40A and 40B, and receiving devices 50A, 50B, 50C, and 50D. have. In the following description, when it is not necessary to distinguish each of the transmission devices 10A, 10B, and 10C, it is described as "transmission device 10." When it is not necessary to distinguish between the wireless access point devices 40A and 40B, the wireless access point devices 40A and 40B are referred to as “wireless access point devices 40”. In addition, when it is not necessary to distinguish each of the receiving devices 50A, 50B, 50C, and 50D, it is described as “receiving device 50”.
[0015]
The transmitting device 10 is connected to the Internet 100 and transmits packets to a multicast group. More specifically, the transmitting device 10A transmits a packet to a multicast group (hereinafter, “multicast group 1”) to which the IP address 239.10.1.1.1 is assigned. The transmitting device 10B transmits a packet to a multicast group (hereinafter, “multicast group 2”) to which the IP address 239.10.1.2 is assigned. The transmitting device 10C transmits a packet to a multicast group (hereinafter, “multicast group 3”) to which the IP address 239.10.3 is assigned.
[0016]
The network switch 30 includes a plurality of interfaces (hereinafter, referred to as “communication ports”) for connecting the node device 20 and the wireless access point device 40, and each of the plurality of communication ports has a unique number (hereinafter, referred to as a “communication port”). , "Port number"). In the communication system shown in FIG. 1, a wireless access point device 40A is connected to a communication port to which port number 1 is assigned, and a wireless access point device 40B is connected to a communication port to which port number 2 is assigned. It is assumed that the node device 20 is connected to the communication port to which the port number 3 is assigned. When the destination of the packet received from the node device 20 is a multicast group, the network switch 30 transmits the packet to the wireless access point device 40A, generates one copy of the packet, and transmits the copy to the wireless access point device 40A. This is transmitted to the point device 40B.
[0017]
An IP address 10.0.1.41 is assigned to the wireless access point device 40A, and an IP address 10.0.1.42 is assigned to the wireless access point device 40B. Each of the wireless access point device 40A and the wireless access point device 40B forms cells 200A and 200B having the same size, and connects to the receiving device 50 in the cell to perform wireless communication. It is assumed that the maximum communication bandwidth in each of the cells 200A and 200B is 11 Mbps.
[0018]
The receiving device 50 connects to the wireless access point device 40 and performs wireless communication. In the communication system shown in FIG. 1, the receiving devices 50A and 50B exist in the cell 200A, and are connected to the wireless access point device 40A. On the other hand, it is assumed that the receiving devices 50C and 50D exist in the cell 200B and are connected to the wireless access point device 40B. It is assumed that the receiving devices 50A and 50B have joined the multicast group 1, the receiving device 50C has joined the multicast group 2, and the receiving device 50D has joined the multicast group 3.
[0019]
The node device 20 is a multicast router that operates in conformity with ECMP, and is connected to the Internet 100 and the network switch 30. The node device 20 stores the above-described maximum communication band (11 Mbps), and stores the maximum communication band and the reception device that is participating in each multicast group acquired by the own device performing an operation conforming to ECMP. A communication band is allocated to each multicast communication flow based on the number of units. Specifically, the node device 20 performs an operation based on the above-described ECMP, and obtains the number of receiving devices participating in each multicast group. In the communication system shown in FIG. 1, the number of receiving devices participating in the multicast group 1 is two (receiving devices 50A and 50B), and the number of receiving devices participating in the multicast group 2 and the multicast group 3 is one. (Only the receiving device 50C has joined the multicast group 2 and only the receiving device 50D has joined the multicast group 3). Then, the node device 20 allocates a communication band in which the maximum communication band is distributed at a ratio of the number of receiving devices participating in each multicast group to each multicast communication flow. That is, the node device 20 allocates a communication bandwidth of 5.5 Mbps to the multicast communication flow addressed to the multicast group 1, and allocates a communication bandwidth of 2.75 Mbps to the multicast communication flows addressed to the multicast groups 2 and 3.
[0020]
As described above, the node device 20 performs an operation conforming to ECMP, so that a communication band having a width proportional to the number of receiving devices participating in the multicast group can be allocated to each multicast communication flow.
[0021]
However, in the communication system shown in FIG. 1, since both the wireless access point devices 40A and 40B directly transmit the packet transmitted from the network switch 30, the wireless access point device 40A connects to its own device. Although the receiving device does not participate in the multicast groups 2 and 3, the packet is transmitted to each of the multicast groups 2 and 3 in the communication band of 2.75 Mbps, and the wireless access point device 40B is Although the receiving device connected to the device does not participate in the multicast group 1, the packet addressed to the multicast group 1 is transmitted in the communication bandwidth of 5.5 Mbps. That is, the communication system shown in FIG. 1 has a problem that both the wireless access point devices 40A and 40B transmit useless packets.
[0022]
IGMP-Snooping is generally known as a technique for eliminating such useless packet transmission. Hereinafter, the function of the network switch having the IGMP-Snooping function will be described. The network switch having the IGMP-Snooping function monitors whether or not IGMP-Report has been received for each communication port, and determines the port number of the communication port that has received IGMP-Report and the IP address of the multicast group that has transmitted IGMP-Report. The correspondence is stored (hereinafter, this correspondence is referred to as “communication port information”). Based on this communication port information, such a network switch does not transfer the IGMP-Report to a communication port other than the communication port to which the node device 20 is connected (the communication port that has received the IGMP-Query). By performing such an operation, the communication port in which the receiving device is present is recognized, and a packet addressed to the multicast group is transmitted only to the communication port to which the receiving device participating in the multicast group is connected. A packet addressed to the multicast group is not transmitted to a communication port to which a receiving device participating in the multicast group is not connected.
[0023]
In the communication system shown in FIG. 1, in order to prevent each wireless access point device 40 from transmitting useless packets, it is conceivable to provide the above-described IGMP-Snooping function to the network switch 30. When the IGMP-Snooping function is given to the network switch 30, the network switch 30 stores communication port information as shown in FIG. 2, and based on the communication port information, the wireless access point device 40A receives only packets addressed to the multicast group 1. And transmits only the packets addressed to the multicast groups 2 and 3 to the wireless access point device 40B. Thus, by giving the IGMP-Snooping function to the network switch 30, useless packets are not transmitted from the wireless access point devices 40A and 40B.
[0024]
However, while the maximum communication band in each cell 200 is 11 Mbps, the wireless access point device 40A transmits only the packet addressed to the multicast group 1 in the 5.5 Mbps communication band, so that the wireless access point device 40A has a bandwidth of 5.5 Mbps. Communication band is unused and free. Since the wireless access point device 40B transmits packets in a communication band of 2.75 Mbps (total of 5.5 Mbps) to each of the multicast groups 2 and 3, the communication band for 5.5 Mbps also has a communication band of 5.5 Mbps. Unused and free.
[0025]
That is, in a case where the node device 20 that performs an operation conforming to ECMP and the network switch 30 having the IGMP-Snooping function are combined, useless transmission of packets by the wireless access point devices 40A and 40B is eliminated. However, the communication band used for transmitting useless packets is not used effectively. As a result, even if an existing technology such as ECMP or IGMP-Snooping is used, a communication band cannot be allocated to a multicast communication flow without waste.
[0026]
The present invention has been made in view of the above-described problems, and has as its object to provide a technique of allocating a communication band to a multicast communication flow without waste while securing a benefit of a receiver who joins a multicast group.
[0027]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has a plurality of wireless access point devices that receive a data block including destination information indicating a destination and wirelessly transmit the data block to a terminal device under the device, and receive the data block. A network switch that transmits the data block only to a wireless access point device having a terminal device of a destination indicated by the destination information of the data block among the plurality of wireless access point devices. And transmitting the data block to the network switch only when the data block is received and the destination indicated by the destination information of the data block is a terminal device under the control of the plurality of wireless access point devices. Means and said plurality of wireless access points Information indicating a wireless access point device having the terminal device under its control and information indicating a multicast group in which the terminal device participates from terminal devices participating in the multicast group among the terminal devices subordinate to the remote device. Acquiring means for acquiring, and based on the information acquired by the acquiring means, for each wireless access point device, sums up the number of terminal devices participating in each multicast group, and the larger the number, the wider the communication bandwidth of the data. Control means for controlling the transmission means so as to transmit the block to the multicast group.
[0028]
Further, in order to achieve the above object, the present invention provides a method for receiving a plurality of wireless access points connected to a network switch which receives a data block including a destination transmitted from a node device and transmits the data block only to the destination. A terminal device that receives the data block wirelessly transmitted from the wireless access point device under the control of any one of the point devices, and determines whether the device itself has joined a multicast group. Only when participating in a multicast group, a wireless access point having information indicating a wireless access point device having its own device under its control and information indicating a multicast group in which its own device is under its own device Transmitting means for transmitting to the node device via a device, A communication band allocated by the node device to transmit the data block addressed to the multicast group in which the node device is participating based on the information transmitted by the communication unit. And receiving means for receiving the data block transmitted in a wider communication band as the number is larger.
[0029]
In order to achieve the above object, the present invention has a plurality of wireless access point devices that receive a data block including destination information indicating a destination and wirelessly transmit the data block to a terminal device under the control, and the data block A network switch that transmits the data block only to a wireless access point device having a destination terminal device indicated by destination information of the data block among the plurality of wireless access point devices. Receiving the data block to a computer device under the control thereof and transmitting the data block to the network switch only when the destination indicated by the destination information of the data block is a terminal device under the control of the plurality of wireless access point devices Transmitting means, and the plurality of wireless access points. Information indicating a wireless access point device having the terminal device under its control and information indicating a multicast group in which the terminal device has joined are transmitted from the terminal devices participating in the multicast group among the terminal devices subordinate to the point device. Acquiring means for acquiring, and based on the information acquired by the acquiring means, for each wireless access point device, sums up the number of terminal devices participating in each multicast group, and the larger the number, the wider the communication bandwidth of the data. A program for realizing control means for controlling the transmission means to transmit a block to a multicast group, and a computer-readable recording medium storing the program are provided.
[0030]
Further, in order to achieve the above object, the present invention provides a method for receiving a plurality of wireless access points connected to a network switch which receives a data block including a destination transmitted from a node device and transmits the data block only to the destination. Under the control of any one of the point devices, the computer device that receives the data block wirelessly transmitted from the wireless access point device determines whether or not the computer device has joined the multicast group. Determining, only when participating in the multicast group, the information indicating the wireless access point device having the computer device under the control and the information indicating the multicast group in which the computer device participates under the control of the computer device Wireless access point Transmitting means for transmitting to the node device via a client device, and communication that allocates the data block to transmission of the data block addressed to the multicast group in which the computer device participates, based on information transmitted by the transmitting device. And receiving means for receiving the data blocks transmitted in a wider communication band as the number increases and the number of terminal devices participating in each multicast group is increased for each wireless access point device. And a computer-readable recording medium on which the program is recorded.
[0031]
When such a node device, a terminal device, a program, and a recording medium are used, when a data block addressed to the multicast group is transmitted from the node device to the network switch, each wireless access point device participates in each multicast group. The larger the number of terminal devices that are located, the wider the communication band is allocated and transmitted.
[0032]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(1) Overall configuration
FIG. 3 is a diagram showing an example of the overall configuration of a communication system having a node device and a terminal device according to the present invention. As shown in this figure, the overall configuration of this communication system differs from the communication system shown in FIG. 1 in that a node device 60 is provided in place of the node device 20 and that the receiving devices 50A, 50B, 50C And 50D in place of receiving devices 70A, 70B, 70C and 70D. In addition, when it is not necessary to distinguish each of the receiving devices 70A, 70B, 70C, and 70D, it is described as “receiving device 70”.
[0033]
The difference between the receiving device 70 and the receiving device 50 is that, in response to a request from the node device 60, the IP address of the wireless access point device 40 to which the own device is connected and the IP address of the multicast group in which the own device participates The point is that the connection information including the address is transmitted to the node device 60. FIG. 4 shows an example of connection information when the receiving device 70 is connected to the wireless access point device 40A and has joined the multicast group 1.
[0034]
The difference between the node device 60 and the node device 20 lies in that a band management table, which will be described later, is stored in place of the maximum communication band of the cell formed by the wireless access point device 40, and that each wireless access point device 40 Requesting that the connection information be transmitted to the reception device 70 connected to the reception device 70, and updating the storage content of the above-described band management table based on the content of the connection information transmitted from each reception device 70. And that a communication band is assigned to each multicast communication flow based on the storage contents of the band management table. FIG. 5 shows an example of the bandwidth management table. As shown in FIG. 5, the band management table includes the IP address of each wireless access point device 40, the maximum communication band of the cell 200 formed by this wireless access point device 40, and the wireless access point device 40 transmitting a packet. 9 is a table in which the IP address of the multicast group, the number of receiving devices participating in the multicast group, and the value of the communication band allocated to the communication flow addressed to the multicast group are stored in association with each other.
[0035]
(2) Configuration of node device 60
FIG. 6 is a block diagram illustrating a configuration example of the node device 60. As shown in this figure, the node device 60 includes a first communication interface unit (hereinafter, referred to as a “first communication IF unit”) 61, a second communication IF unit 62, a routing control unit 63, It has a unit 64, a queue control unit 65, and a band control unit 66.
[0036]
The first communication IF unit 61 receives a packet transmitted from the transmission device 10 via the Internet 100, passes the packet to the routing control unit 63, and transmits the packet passed from the routing control unit 63 to the Internet. Has a function. The second communication IF unit 62 has a function of receiving the packet transmitted from the network switch 30, passing the packet to the routing control unit 63, and transmitting the packet passed from the routing control unit 63 to the network switch 30. are doing. Further, the first communication IF unit 61 performs an operation according to a multicast protocol such as PIM-SM (Protocol Independent Multicast-Sparse Mode) or DVMRP (Distance Vector Multicast Routing Protocol), and the second communication IF unit 62. The first communication IF unit 61 and the second communication IF unit 62, which perform an operation in accordance with IGMP, perform such an operation, so that the path of the multicast communication flow from the transmission device 10 to the reception device 70 is performed. Has been established.
[0037]
The routing control unit 63 determines whether to transmit the packet to the local network or the Internet based on the destination of the packet passed from the first communication IF unit 61 or the second communication IF unit 62, and transmits the packet to the local network. When it is determined that the packet is to be transmitted, the packet is passed to the second communication IF unit 62, and when it is determined that the packet is transmitted to the Internet, the packet is passed to the first communication IF unit 61. .
[0038]
The information holding unit 64 is a storage device that stores information such as a hard disk in a nonvolatile manner, and stores the above-described band management table (see FIG. 5).
[0039]
The queue control unit 65 causes the second communication IF unit 62 to transmit a packet addressed to the multicast group in a communication band stored in the band management table (see FIG. 5) in association with the IP address of the multicast group. It has a control function.
[0040]
The band control unit 66 has a function of periodically updating the storage contents of the above-mentioned band management table. Although the details will be described later, the band control unit 66 has a clock function for obtaining the current time, and only when the current time obtained by the clock function matches a predetermined time, the bandwidth control unit 66 A message requesting transmission is generated, and the message is transmitted to all the receiving devices 70 via the second communication IF unit 62. Then, the bandwidth control unit 66 receives the connection information transmitted from each receiving device 70 via the second communication IF unit 62, and updates the storage content of the above-described bandwidth management table based on the content of the received connection information. I do.
[0041]
(3) Operation example
The operation in which the node device 60 allocates a communication band to each multicast communication flow in the communication system shown in FIG. 3 will be described with reference to FIG.
[0042]
(3-1) Operation example 1
First, as a premise of this operation example, it is assumed that the receiving devices 70A and 70B are in the cell 200A, are connected to the wireless access point device 40A, and have joined the multicast group 1. It is also assumed that the receiving devices 70C and 70D are in the cell 200B and are connected to the wireless access point device 40B. It is assumed that the receiving device 70C has joined the multicast group 2 and the receiving device 70D has joined the multicast group 3. A band management table shown in FIG. 5 is stored in the information holding unit 64 of the node device 60. As shown in this figure, the communication flow addressed to the multicast group 1 has a communication bandwidth of 5.5 Mbps. It is assumed that a communication band of 2.75 Mbps is assigned to both communication flows addressed to the multicast groups 2 and 3.
[0043]
FIG. 7 is a flowchart illustrating the flow of the bandwidth allocation process executed by the bandwidth control unit 66 of the node device 60. As shown in the figure, the band control unit 66 first obtains the current time by using a clock function (step SA1), and determines whether the current time matches a predetermined time (step SA1). Step SA2). When it is determined that the current time does not match the predetermined time, the band control unit 66 repeatedly executes the processing from step SA1 onward, and conversely, when the current time matches the predetermined time. If it is determined, the process from step SA3 is performed. In the present operation example, a case will be described in which the current time acquired by the band control unit 66 matches a predetermined time.
[0044]
In step SA3, the bandwidth control unit 66 generates a request message requesting transmission of connection information, and transmits the request message to the IP address 224.0.0.1. This IP address 224.0.0.1 is a special IP address meaning that all the receiving devices in the local network are destinations. Then, the bandwidth control unit 66 that has completed transmitting the request message allocates the IP address of the multicast group stored in the bandwidth management table, the number of receiving devices participating in the multicast group, and each multicast group. The communication band is deleted, and the band management table is initialized (step SA4).
[0045]
The request message transmitted from the node device 60 reaches the network switch 30 via the communication line. Upon receiving the request message, the network switch 30 transmits the request message to the wireless access point device 40A, generates one copy of the request message, and transmits the copy to the wireless access point device 40B.
[0046]
The two request messages transmitted from the network switch 30 reach the wireless access point devices 40A and 40B via respective individual communication lines. Upon receiving this request message, each of the wireless access point devices 40A and 40B sends this request message to a cell formed by the own device.
[0047]
The request message transmitted to the cells 200A and 200B is received by the receiving device 70 connected to each wireless access point device 40 in each cell 200. The receiving device 70 that has received the request message reads out the connection information stored in the own device, and transmits a response message including the connection information to the node device 60. The response message transmitted from each receiving device 70 reaches the node device 60 via the wireless access point device 40 and the network switch 30 to which each receiving device 70 is connected in order.
[0048]
The band control unit 66 of the node device 60 receives the response messages transmitted from each receiving device 70 via the second communication IF unit 62, and acquires the connection information included in each response message (step SA5). . Then, the band control unit 66 updates the storage contents of the band management table stored in the information holding unit 64 based on the connection information (step SA6).
[0049]
More specifically, in the present operation example, the band control unit 66 acquires a total of four pieces of connection information transmitted from each of the receiving devices 70A, 70B, 70C, and 70D. The bandwidth control unit 66 first classifies these four pieces of connection information according to the IP address of the wireless access point device 40 included in each connection information, and further includes the IP address of the same wireless access point device 40. Is classified according to the IP address of the multicast group included in each piece of connection information. In this operation example, the four pieces of connection information transmitted from each receiving device 70 are classified into the following three groups. The first group is a group of connection information including the IP address of the wireless access point device 40A and the IP address of the multicast group 1, and the connection information obtained from the reception devices 70A and 70B belongs to this group. I have. The second group is a group of connection information including the IP address of the wireless access point device 40B and the IP address of the multicast group 2, and the connection information acquired from the receiving device 70C belongs to this group. The third group is a group of connection information including the IP address of the wireless access point device 40B and the IP address of the multicast group 3, and the connection information acquired from the reception device 70D belongs to this group. Then, the bandwidth control unit 66 associates the IP address of the wireless access point device 40 included in the connection information belonging to each group, the IP address of the multicast group, and the number of connection information belonging to each group. It is stored in the bandwidth management table.
[0050]
Next, the band control unit 66 determines the maximum communication band associated with each wireless access point device 40, the number of multicast groups to which the wireless access point device 40 is transmitting packets, and , And determines a communication band to be allocated to a communication flow addressed to each multicast group based on the number of receiving devices 70 participating in each multicast group, and stores the communication band in the band management table. Specifically, since the wireless access point device 40A transmits only the packet addressed to the multicast group 1 to the cell 200A, the bandwidth control unit 66 allocates 11 Mbps, which is the maximum communication bandwidth in the cell 200A, to the multicast group 1. Also, the wireless access point device 40B transmits packets addressed to the multicast groups 2 and 3, and the number of receiving devices participating in the multicast groups 2 and 3 is one each. A communication band obtained by distributing the maximum communication band of 11 Mbps at a ratio of 1: 1 is allocated to the multicast groups 2 and 3.
[0051]
As described above, by updating the storage content of the bandwidth management table based on the connection information acquired from the receiving device 70 by the bandwidth control unit 66, the storage content of the bandwidth management table becomes the state shown in FIG. Hereinafter, the queue control unit 65 of the node device 60 transmits the packet addressed to each multicast group in the communication band stored in the band management table (see FIG. 8) in association with the IP address of the multicast group. By controlling the second communication IF unit 62, a communication band of 11 Mbps is allocated to the communication flow destined for the multicast group 1, and both the communication flow destined for the multicast group 2 and the communication flow destined for the multicast group 3 have a transmission rate of 5.5 Mbps. A communication band is allocated.
[0052]
(3-2) Operation example 2
Next, a band management table shown in FIG. 8 is stored in the information holding unit 64 of the node device 60. As shown in this figure, a communication band of 11 Mbps is allocated to the communication flow addressed to the multicast group 1. It is assumed that a communication band of 5.5 Mbps is assigned to the communication flows addressed to the multicast groups 2 and 3. Also, the receiving devices 70A and 70B connect to the wireless access point device 40A and participate in the multicast group 1, the receiving devices 70C and 70D connect to the wireless access point device 40B, and the receiving device 70C joins the multicast group 2. It is assumed that the receiving device 70D has participated in the multicast group 3. In such a situation, only the receiving device 70B releases the connection with the wireless access point device 40A, moves from the cell 200A to the cell 200B, connects to the wireless access point device 40B, and joins the multicast group 2. The operation will be described.
[0053]
Only when the current time obtained by the node device 60 using the clock function matches the predetermined time, the node device 60 transmits a request message to the receiving device 70 requesting that the connection information be transmitted to the own device, The operation of the node device 60 until the band management table is initialized is the same as the operation of the node device 60 in step SA1 to step SA4 in the operation example 1 described above. The operation of each device of the network switch 30, the wireless access point device 40, and the receiving device 70 until the response message to the request message reaches the node device 60 is the same as the operation of each device in the operation example 1. . Further, the bandwidth control unit 66 of the node device 60 acquires the connection information transmitted from each receiving device 70 and updates the storage content of the bandwidth management table stored in the information holding unit 64 based on the connection information. The operation is the same as the operation of Step SA5 and Step SA6 of the node device 60 in Operation Example 1 described above.
[0054]
However, since the content of the connection information received from each receiving device 70 is different from the content of the connection information in Operation Example 1, the storage content of the bandwidth management table is updated with the storage content different from that in Operation Example 1. Specifically, since the wireless access point device 40A transmits only the packet addressed to the multicast group 1 to the cell 200A, the bandwidth control unit 66 sets the maximum communication bandwidth in the cell 200A at 11 Mbps to the communication flow addressed to the multicast group 1. Assign to Also, the wireless access point device 40B transmits packets addressed to the multicast groups 2 and 3, and two receiving devices (receiving devices 70B and 70C) have joined the multicast group 2 and have joined the multicast group 3. Since the number of receiving devices is one (receiving device 70D), a communication band in which 11 Mbps, which is the maximum communication band in the cell 200B, is distributed at a ratio of 2: 1 is allocated to the multicast groups 2 and 3. That is, the band control unit 66 allocates a communication band of 7.3 Mbps to the multicast group 2 and allocates a communication band of 3.7 Mbps to the multicast group 3.
[0055]
As described above, when the bandwidth control unit 66 updates the storage content of the bandwidth management table based on the connection information acquired from the receiving device 70, the storage content of the bandwidth management table becomes the state shown in FIG. Hereinafter, the queue control unit 65 of the node device 60 transmits the packet addressed to each multicast group in the communication band stored in the band management table (see FIG. 9) in association with the IP address of the multicast group. By controlling the second communication IF unit 62, a communication flow of 11 Mbps is allocated to the communication flow destined for the multicast group 1 and a communication band of 7.3 Mbps is allocated to the communication flow destined for the multicast group 2. A communication bandwidth of 3.7 Mbps is allocated to the communication flow addressed to group 3.
[0056]
(4) Modified example
(4-1) Modification 1
In the above-described embodiment, a case has been described where a packet is used as an example of a data block. However, the data block transmitted and received by the node device according to the present invention is not limited to a packet, and may be a frame. In short, any data block may be used as long as the data block includes divided data obtained by dividing data by the data size of the communication unit and information indicating the destination of the data.
[0057]
(4-2) Modification 2
Although the IP multicast has been described as an example of the multicast in the above-described embodiment, the multicast to which the node device according to the present invention allocates the communication band is not limited to the IP multicast. For example, the multicast may be realized in a protocol layer lower than the network layer. Specifically, multicast using a MAC address which is a communication address in the data link layer may be used.
[0058]
(4-3) Modification 3
In the above-described embodiment, the case where the node device 60 controls the allocation of the communication band in the wireless LAN has been described. However, the network in which the node device according to the present invention controls the allocation of the communication band is limited to the wireless LAN. Instead, a mobile packet communication network may be used. As means for realizing multicast in a mobile packet communication network, it is realized by setting a packet transmission destination to a specific destination indicating a multicast group.
[0059]
(4-4) Modification 4
In the above-described embodiment, the case has been described where the node device 60 allocates a communication band in the cell 200 formed by the wireless access point device 40 directly connected to the network switch 30 connected thereto. The wireless access point device 40 forming the cell in which the node device 60 manages the communication band may not be directly connected to the network switch 30. For example, a wireless access point device forming a cell in which the node device 60 manages a communication band is a wireless access point device connected to a plurality of network switches connected to the network switch 30 connected to the node device 60. May be.
[0060]
(4-5) Modification 5
In the above-described embodiment, a case has been described in which the band control unit 66 of the node device 60 has a timekeeping function, and it is determined whether or not a certain time has elapsed by using the timekeeping function. May be provided separately with a timekeeping unit having a timekeeping function. Specifically, the timer is made to determine whether or not a certain time has elapsed, and only when it is determined that the certain time has elapsed, the time from the timer to the band control unit 66 is notified that the certain time has elapsed. Notify. Then, the band control unit 66 that has received the notification may perform the processing after step SA3 of the above-described band control processing.
[0061]
(4-6) Modification 6
In the above-described embodiment, the case has been described where the bandwidth control unit 66 of the node device 60 initializes the bandwidth management table after transmitting the request message to all the receiving devices 70 under its own device. The bandwidth management table may be initialized just before the unit 66 updates the storage content of the bandwidth management table. In addition, a work table having the same table format as the bandwidth management table is provided, and the work table includes the number of reception devices for each wireless access point device and each multicast group calculated based on the connection information acquired from each reception device 70. And a communication band to be allocated to each multicast group, and the contents stored in the work table may be overwritten on the band management table.
[0062]
(4-7) Modification 7
In the above-described embodiment, the node device 60 stores the maximum communication band in the cell formed by each wireless access point device 40 in association with the IP address of the wireless access point device 40 forming the cell. A case has been described in which the communication band obtained by dividing the maximum communication band by a width proportional to the number of receiving devices participating in each multicast group is assigned to each multicast communication flow, but the node device 60 stores the maximum communication band. You don't have to. For example, as the number of receiving devices participating in each multicast group increases for each wireless access point device calculated based on the connection information acquired from each receiving device 70, the node device 60 65 may be used to increase the amount of packets transmitted to each multicast group.
[0063]
(4-8) Modification 8
In the above-described embodiment, for each wireless access point device calculated based on the connection information acquired from each receiving device 70, the number of receiving devices participating in each multicast group and the width of the communication band allocated to each multicast group Has been described, but the relationship between the number of receiving devices participating in each multicast group and the width of the communication band allocated to the multicast group for each wireless access point device is not limited to proportional. For example, for example, the width of the communication bandwidth allocated to each multicast group may be proportional to the square of the number of receiving devices participating in each multicast group for each wireless access point device, and the number of receiving devices You may make it proportional to logarithm (for example, common logarithm). The point is that the larger the number of the receiving devices, the more the communication band that is wider is allocated to the multicast group.
[0064]
(4-9) Modification 9
In the above-described embodiment, only the case where the node device 60 allocates the communication band to the multicast communication flow has been described. However, the node device 60 may allocate the communication band to both the multicast communication flow and the unicast communication flow. Of course you can. Specifically, by regarding the unicast communication flow as a multicast communication flow addressed to a multicast group in which only one receiving device participates, the node device 60 can perform both the multicast communication flow and the unicast communication flow. As the number of receiving devices that receive each communication flow increases for each wireless access point device, a wider communication band can be allocated.
[0065]
(4-10) Modification 10
In the embodiment described above, the node device 60 obtains connection information including the IP address of the wireless access point device 40 connected from each receiving device 70 and the IP address of the participating multicast group, and The case has been described where the content of the bandwidth management table stored in the device is updated based on this connection information and the communication bandwidth is allocated to each multicast communication flow. It may have an authentication function for judging sex.
[0066]
Specifically, information indicating the validity of the own device (for example, an electronic certificate issued by a trusted certificate authority) is stored in the receiving device 70 in advance, and the receiving device 70 transmits the connection information to the node device 60. When this is done, this electronic certificate is also transmitted. The node device 60 can determine the validity of the receiving device 70 by determining the presence or absence of the digital certificate.
[0067]
In this way, by having the node device 60 determine the validity of each receiving device 70, the connection information is transmitted many times by impersonating another device, and whether a large number of receiving devices 70 have joined the same multicast group It is possible to prevent an unauthorized act such as causing the node device 60 to allocate a large communication band.
[0068]
(4-11) Modification 11
In the embodiment described above, the node device 60 periodically requests that all the receiving devices 70 managed by the node device 60 transmit the connection information, and the connection information transmitted from each of the receiving devices 70 in response to this request. Has been described, the manner in which the node device 60 acquires the connection information from each of the receiving devices 70 is not limited to such a mode. For example, the receiving device 70 periodically transmits the information. The node device 60 may receive and acquire the connection information. Alternatively, the node device 60 may acquire the connection information when the receiving device 70 notifies the node device 60 of the participation in the multicast group. There may be.
[0069]
First, the manner in which the node device 60 receives and acquires connection information periodically transmitted by the receiving device 70 will be specifically described. A timekeeping function for acquiring the current time is provided in the receiving device 70, and when the current time acquired by the timekeeping function matches a predetermined time, the receiving device 70 transmits the connection information stored in its own device. This aspect is realized by transmitting the connection information to the node device 60 and receiving and acquiring the connection information.
[0070]
Next, a specific description will be given of a mode in which the node device 60 acquires connection information when the receiving device 70 notifies the node device 60 of participation in the multicast group. When the receiving device 70 notifies the node device 60 of the participation in the multicast group, the receiving device 70 transmits connection information including the IP address of the joining multicast group and the IP address of the connected wireless access point device to the node device 60. This aspect is realized by transmitting the connection information to the device 60 and receiving and acquiring the connection information by the node device 60.
[0071]
(4-12) Modification 12
In the above-described embodiment, a case has been described in which a multicast router is used as an example of the node device 60 according to the present invention. By executing the program, the same functions as those of the multicast router described above may be added to these computer devices.
[0072]
Specifically, a program for realizing the function of the node device according to the present invention is recorded on a computer-readable recording medium such as a compact disk-read only memory (CD-ROM) or a floppy disk (FD). The program recorded on the recording medium is read by a computer equipped with a device (for example, a CD-ROM drive or an FD drive) capable of reading information recorded on the recording medium. This is realized by causing the CPU (Central Processing Unit) of the computer device to execute the read program.
[0073]
In addition, by causing a general computer device such as a mobile phone, a PDA, or a PC to execute a program for realizing the function of the terminal device according to the present invention, the computer device has the same function as the receiving device 70 described above. May be added.
[0074]
Specifically, a program for realizing the function of the terminal device according to the present invention is recorded on a computer-readable recording medium, and information recorded on such a recording medium can be read. This is realized by causing a computer device equipped with a device (for example, a CD-ROM drive or an FD drive) to read a program recorded on the recording medium and causing the CPU of the computer device to execute the read program.
[0075]
【The invention's effect】
According to the present invention, the width of the communication band allocated to the multicast communication flow becomes wider as the number of receiving devices participating in the multicast group, which is the destination of the multicast communication flow, becomes wider. In a multicast communication flow addressed to a multicast group having a large number of packets, dropout of packets is less likely to occur, and there is an effect that a benefit of a receiver receiving the multicast data is secured.
[0076]
Further, according to the present invention, a communication band usable when data is transmitted from a wireless access point device to each multicast group is set to a receiving device which is participating in a multicast group to which the wireless access point device is transmitting data. Since the communication band divided by the width according to the number of the communication flows is allocated, it is possible to effectively allocate the communication band to each multicast communication flow.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of the overall configuration of a communication system having a conventional node device 20.
FIG. 2 is a diagram showing an example of communication port information stored in the network switch 30.
FIG. 3 is a block diagram illustrating an example of an overall configuration of a communication system including a node device 60 and a receiving device 70 according to the present invention.
FIG. 4 is a diagram showing an example of connection information stored in a receiving device 70 configuring the system.
FIG. 5 is a diagram showing an example of storage contents of a bandwidth management table stored in the node device 60.
FIG. 6 is a diagram showing a configuration example of the node device 60.
FIG. 7 is a flowchart showing a flow of a bandwidth allocation process executed by the node device 60;
FIG. 8 is a diagram showing an example of the contents of a bandwidth management table stored in the node device 60;
FIG. 9 is a diagram showing an example of the contents of a bandwidth management table stored in the node device 60;
[Explanation of symbols]
10A, 10B, 10C: transmitting device, 20, 60: node device, 30: network switch, 40A, 40B: wireless access point device, 50A, 50B, 50C, 50D, 70A, 70B, 70C, 70D: receiving device, 61 ... first communication IF unit, 62 ... second communication IF unit, 63 ... routing control unit, 64 ... information holding unit, 65 ... queue control unit, 66 ... bandwidth control unit, 100 ... Internet, 200A, 200B ... cell.

Claims (10)

A network switch that receives a data block including destination information indicating a destination and wirelessly transmits the data block to a terminal device under the destination, and receives the data block; In a node device having a network switch that transmits the data block only to a wireless access point device having a subordinate terminal device indicated by the destination information of the data block among the access point devices,
A transmitting unit that receives the data block, and transmits the data block to the network switch only when the destination indicated by the destination information of the data block is a terminal device under the control of the plurality of wireless access point devices;
The information indicating the wireless access point device having the terminal device under its control and the multicast group in which the terminal device participates are obtained from the terminal devices belonging to the multicast group among the terminal devices under the plurality of wireless access point devices. Acquisition means for acquiring information indicating
Based on the information obtained by the obtaining unit, the number of terminal devices participating in each multicast group is totaled for each wireless access point device, and the larger the number, the more the data block is transmitted to the multicast group in a wider communication band. And a control unit for controlling the transmission unit so as to perform the transmission. Further comprising storage means for storing information uniquely identifying each of the plurality of wireless access point devices and the maximum communication band of the wireless access point device specified by the information in association with each other,
The control means counts, for each wireless access point device, the number of terminal devices participating in each multicast group, allocates a wider communication band as the number increases, and the sum of the communication band corresponds to the wireless access point device. 2. The node device according to claim 1, wherein the transmission unit is controlled so as not to exceed a maximum communication band stored in the storage unit. A clock means for obtaining the current time;
Only when the current time obtained by the clocking means is a predetermined time, among the terminal devices under the plurality of wireless access point devices, a terminal device participating in a multicast group, Request means for requesting transmission of information indicating a wireless access point device under its control and information indicating a multicast group in which the terminal device has joined to its own device;
Further comprising
The node device according to claim 1, wherein the acquisition unit receives and acquires information transmitted from a terminal device that has requested transmission of the information by the request unit. The acquisition means,
A terminal device provided with a clock unit for acquiring a current time, the terminal device having a terminal device periodically transmitted from a terminal device participating in a multicast group under the plurality of wireless access point devices. The node device according to claim 1, wherein the node device receives and acquires information indicating a wireless access point device and information indicating a multicast group in which the terminal device has joined. The acquisition means,
Receive and obtain information transmitted from a terminal device instructed by the user to join the multicast group, indicating information indicating a wireless access point device under the terminal device and information indicating the multicast group instructed to be joined by the user The node device according to claim 1, wherein A determination unit configured to determine whether the terminal device that has transmitted the information indicating the wireless access point device having its own device and the information indicating the multicast group in which the own device has joined is a legitimate terminal device; Prepare,
2. The node device according to claim 1, wherein the acquisition unit receives and acquires only information transmitted from a terminal device determined to be a legitimate terminal device by the determination unit. Subordinate to one of the plurality of wireless access point devices connected to the network switch that receives the data block including the destination transmitted from the node device and transmits the data block only to the destination. In a terminal device that receives the data block wirelessly transmitted from the wireless access point device,
It is determined whether or not the own device has joined the multicast group. Only when the own device has joined the multicast group, information indicating the wireless access point device having its own device and the multicast group in which the own device has joined Transmitting means for transmitting to the node device via a wireless access point device having its own device and information indicating,
A communication band allocated to the transmission of the data block addressed to the multicast group in which the node device is based on the information transmitted by the transmission unit. Receiving means for counting the number of participating terminal devices and receiving the data block transmitted in a wider communication band as the number increases. A network switch that receives a data block including destination information indicating a destination and wirelessly transmits the data block to a terminal device under the destination, and receives the data block; A computer device having a network switch that transmits the data block only to a wireless access point device having a subordinate terminal device indicated by the destination information of the data block among the access point devices,
A transmitting unit that receives the data block, and transmits the data block to the network switch only when the destination indicated by the destination information of the data block is a terminal device under the control of the plurality of wireless access point devices;
The information indicating the wireless access point device having the terminal device under its control and the multicast group in which the terminal device participates are obtained from the terminal devices belonging to the multicast group among the terminal devices under the plurality of wireless access point devices. Acquisition means for acquiring information indicating
Based on the information obtained by the obtaining unit, the number of terminal devices participating in each multicast group is totaled for each wireless access point device, and the larger the number, the more the data block is transmitted to the multicast group in a wider communication band. And a control means for controlling the transmission means to perform the transmission. A data block including a destination transmitted from the node device, and the data block being transmitted to only the destination under the control of any one of the plurality of wireless access point devices connected to the network switch In a computer device that receives the data block wirelessly transmitted from the wireless access point device,
It is determined whether or not the computer device has joined the multicast group, and only when the computer device has joined the multicast group, information indicating the wireless access point device having the computer device under control and the computer device have joined Transmitting means for transmitting information indicating the multicast group to the node device via a wireless access point device having the computer device under its control,
A communication band assigned by the node device to transmit the data block addressed to the multicast group in which the computer device participates, based on the information transmitted by the transmission means, wherein each multicast group is And a receiving means for receiving the data blocks transmitted in a wider communication band as the number of terminal devices participating in the communication is larger and the number is larger. A computer-readable recording medium on which the program according to claim 8 is recorded.

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