JP3678634B2 - Broadcast communication system - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a broadcast communication system, and more particularly to a broadcast communication system in a server-client system using a wireless LAN including a server, an access point provided for the server, and a client provided for the access point. About.
[0002]
[Prior art]
In a server / client system using a conventional wireless LAN, a server and a WAP (wireless access point) at the time of file transfer using multicast communication transmit a transmission frame to all target clients. Further, in file transfer using conventional multicast communication, communication between the WAP and the client is performed almost simultaneously.
[0003]
[Problems to be solved by the invention]
However, in the server / client system using the conventional wireless LAN described above, communication between all WAPs and the target client is performed almost simultaneously and with a high load when transferring various files using multicast communication. Therefore, there is a drawback in that errors in the transferred data frame frequently occur due to radio wave interference between WAPs.
[0004]
In addition, since the client that has not received the data requests the server to retransmit the data frame, the server frequently retransmits the client. Therefore, the load on the server, the server and the WAP There is a disadvantage that the load on the network becomes heavy.
[0005]
In addition, when various files are transferred using multicast communication, all WAPs perform high-load communication and the communication bandwidth is occupied. Therefore, a client that is not subject to multicast communication performs unicast communication with the server. There is a drawback that the communication performance is remarkably deteriorated.
[0006]
A first object of the present invention is to provide a broadcast communication system capable of reducing the occurrence of data frame errors during multicast communication.
[0007]
A second object of the present invention is to provide a server / client system and its broadcast communication system capable of reducing the load on the server and the network load between the server and the WAP.
[0008]
A third object of the present invention is to provide a broadcast communication system capable of performing communication without greatly degrading the communication performance of clients not subject to multicast communication during multicast communication.
[0009]
[Means for Solving the Problems]
The broadcast communication system of the present invention is a broadcast communication system in a server-client system using a wireless LAN including a server, an access point provided for the server, and a client provided for the access point. When the server performs multicast communication, the server transmits to the access point at a transmission time interval according to a ratio between the number of clients belonging to the server that has made a multicast distribution request and the number of all clients belonging to the server. A data frame is transmitted.
[0010]
Further, in the broadcast communication method, the access point has a transmission time interval according to a ratio between the number of clients belonging to the access point that has made the multicast distribution request and the number of all clients belonging to the access point, The data frame from the server is transmitted to a client belonging to the access point that has made the multicast distribution request.
[0011]
Further, in the broadcast communication method, the access point includes holding means for holding the data frame from the server, and a client belonging to the access point that has made the multicast distribution request is sent from the access point. When at least one of the data frames is not received, when the first retransmission request is made to retransmit the corresponding data frame to itself, the client that has made the first retransmission request is notified to the holding unit. The held data frame is retransmitted.
[0012]
Still further, in the broadcast communication method, when the access point receives the first retransmission request and does not hold the corresponding data frame in the holding unit, the access point resends the corresponding data frame to the server. In response to the request, the server retransmits the data frame to the client that has made the first retransmission request via the access point.
[0013]
The operation of the present invention is as follows. When performing multicast communication, the client makes a multicast distribution request to the server via the WAP to which the client belongs. In response to this distribution request, the server calculates the ratio between the number of all clients belonging to itself and the number of clients belonging to itself that made the distribution request, and determines the transmission time interval of data frames to be transmitted. In addition, since the WAP monitors the exchange between the server and the client belonging to itself, the WAP can calculate the ratio between the number of all clients belonging to the server and the number of clients belonging to the client who has made a distribution request. The transmission time interval of the received data frame is determined.
[0014]
Then, the server transmits data frames to the WAP at the above transmission time interval, and the WAP holds several data frames in the buffer and transmits them to the client at the above transmission time interval. Here, when the client fails to receive the data frame, the client requests the WAP to retransmit the corresponding data frame. When the WAP receives this retransmission request and there is a corresponding data frame in the buffer, the WAP retransmits the corresponding data frame to the client that requested the retransmission, and when there is no corresponding data frame in the buffer, the WAP retransmits the corresponding data frame to the server. To request. Upon receiving this retransmission request, the server retransmits the corresponding data frame to the client that requested the retransmission via WAP.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a server / client system according to an embodiment of the present invention. The server / client system to which the present invention is applied is constructed by, for example, a server 101, WAPs 102 and 111, and clients (200 to 203 and 300 to 302) in an area 103 as shown in FIG.
[0016]
Each of the WAPs 102 and 111 is connected to the server 101 via a wired line 104. The clients (200 to 203) in the area 106 in the area 103 are connected to the WAP 102 via a wireless line, and the clients (300 to 302) in the area 112 in the area 103 are connected to the WAP 111 via a wireless line. Yes.
[0017]
That is, the WAPs 102 and 111 are provided for the server 101, the client in the area 106 is provided for the WAP 102, and the client in the area 112 is provided for the WAP 111. The client belonging to the server 101 is a client in the area 103, the client belonging to the WAP 102 is a client in the area 106, and the client belonging to the WAP 111 is a client in the area 112.
[0018]
The server 101 transmits a data frame to the clients in the area 103 using the wired line 104. The IP (Internet Protocol) address and the MAC (Media Access Control) address of all clients in the area 103 belonging to the server 101 or The client registration table 105 for registering the client information having any one of these and the presence / absence of the multicast distribution request of the client in the area 103 in association with each other.
[0019]
Each of the WAPs 102 and 111 performs wireless communication with the clients in the areas 106 and 112 by changing the data frame received from the server 101 via the wired line 104 into a wireless signal. The WAP 102 has a client registration table 107 that registers the client information of all clients in the area 106 provided for the WAP 102 and the presence / absence of the multicast distribution request of the clients in the area 106 in association with each other. Furthermore, the WAP 102 has a buffer 108 for holding several data frames transmitted from the server 101.
[0020]
Similarly to the WAP 102, the WAP 111 includes a client registration table 113 for registering the client information of all the clients in the area 112 provided for itself and the presence / absence of the multicast distribution request of the clients in the area 112 in association with each other. And a buffer 114 for holding several data frames transmitted from the server 101.
[0021]
When performing multicast communication, the server 101 transmits names and version information of various files to the clients in the area 103 via the WAPs 102 and 111. The client in the area 103 receives the names and version information of these various files, and returns the presence / absence of a multicast distribution request to the server 101. The server 101 registers the returned information in the client registration table 105 in association with the already registered client information.
[0022]
The WAPs 102 and 111 monitor the exchange between the server 101 and the clients in the area 106 and the area 112, respectively, and register the client in association with the presence or absence of the distribution request of the clients in the areas 106 and 112 with the already registered client information. Register in the tables 107 and 113, respectively.
[0023]
The server 101 ends acceptance of the multicast distribution request after a predetermined time has elapsed or after all the distribution requests from the clients in the area 103 have been registered in the client registration table 105. After the acceptance is completed, the server 101 determines the number of clients (for example, 201, 202, 300, and 301) that have made distribution requests based on the contents of the client registration table 105, or the clients that have not performed (for example, 200, 203, and 302). ) To determine the number of distribution targets.
[0024]
After the above acceptance, the WAPs 102 and 111 are based on the contents of the client registration tables 107 and 113, or the number of clients (for example, 201 and 202 for the WAP102, 300 and 301 for the WAP111) that have made distribution requests, or not. The number of clients (for example, 200 and 203 in WAP102, 302 in WAP111) is calculated, and the number of distribution targets is determined.
[0025]
The server 101 calculates the ratio between the number of distribution targets and the total number of clients in the area 103 determined from the number of client information registered in the client registration table 105. The WAPs 102 and 111 also calculate the ratio between the number of distribution targets and the total number of clients in the areas 106 and 112 determined from the number of client information registered in the client registration tables 107 and 113, respectively.
[0026]
FIG. 2 is a diagram showing an example of a method for calculating the transmission time interval of the server 101 shown in FIG. In FIG. 2, the total number of clients in the area 103 is 100, for example, the number of distribution targets is 80, for example, and the predetermined minimum transmission time interval is 50 ms, for example. By dividing the minimum transmission time interval by the ratio between the total number of clients and the distribution target number, the transmission time interval (about 60 ms) of the data frame transmitted from the server 101 is calculated.
[0027]
FIG. 3 is a diagram showing an example of a method for calculating the transmission time interval of the WAP 102 shown in FIG. In FIG. 3, the total number of clients in the area 106 is 10, for example, the number of distribution targets is 5, for example, and the predetermined minimum transmission time interval is 80 ms, for example. By dividing the minimum transmission time interval by the ratio of the total number of clients and the distribution target number, the transmission time interval (160 ms) of the data frame transmitted from the WAP 102 is calculated. Note that the calculation method of the transmission time interval of the WAP 111 is the same as that in FIG.
[0028]
The server 101 starts transmitting data frames at a transmission time interval (about 60 ms) corresponding to the above ratio.
[0029]
FIG. 4 is a diagram showing a configuration of a server / client system in which the server 101, WAP 102, and client 201 in the area 106 shown in FIG. 1 are extracted, and the same parts as those in FIG. In FIG. 4, the WAP 102 holds several data frames transmitted from the server 101 in the buffer 108 and transmits data frames at a transmission time interval (160 ms) according to the above ratio.
[0030]
The client 201 receives the data frame transmitted from the WAP 102. If the client 201 fails to receive the data frame, the client 201 requests the WAP 102 to retransmit the data frame that cannot be received. When receiving a retransmission request from the client 201, the WAP 102 retransmits the corresponding data frame to the client 201 when holding the corresponding data frame in the buffer 108.
[0031]
In response to the above retransmission request, the WAP 102 makes a retransmission request to the server 101 when the buffer 108 does not hold the corresponding data frame. When the server 101 receives the retransmission request from the WAP 102, the server 101 distributes the corresponding data frame to the client 201 via the WAP 102.
[0032]
FIG. 5 is a flowchart showing an operation when performing multicast communication of the server / client system according to the embodiment of the present invention. In FIG. 5, the server 101 registers the client information of all the clients in the area 103 belonging to itself in the internal client registration table 105 (step S1). The WAPs 102 and 111 register the client information of all the clients in the areas 106 and 112 provided correspondingly to the internal client registration tables 107 and 113, respectively (step S2).
[0033]
When the registration is completed, the server 101 transmits various file names and version information to each client in the area 103 (step S3). Upon receiving these pieces of information (step S4), the client in the area 103 returns the presence / absence of a multicast distribution request to the server 101 (step S5). The client in the area 103 that has requested distribution (step S6) waits for multicast distribution (step S7), and the client in the area 103 that has not requested distribution (step S6) waits as it is (step S20). The server 101 registers in the client registration table 105 the presence / absence of a distribution request, which is return information of the client in the area 103 (step S8).
[0034]
During this time, the WAPs 102 and 111 monitor the exchange between the server 101 and the client in the area 103, and register the presence / absence of a distribution request, which is the return information of the clients in the areas 106 and 112, in the client registration tables 107 and 113, respectively (step S9). ). The server 101 finishes accepting the distribution request after a predetermined time has elapsed or after registering the presence / absence of the distribution request of all clients in the area 103 (step S10).
[0035]
The server 101 calculates a transmission time interval based on the contents of the client registration table 105 (step S11). In addition, the WAPs 102 and 111 calculate the transmission time intervals based on the contents of the client registration tables 107 and 113 (step S12). The server 101 starts data frame transmission at the calculated transmission time interval (step S13).
[0036]
Each of the WAPs 102 and 111 holds several data frames transmitted from the server 101 in the internal buffers 108 and 114 (step S14), and simultaneously transmits the data frames at the calculated transmission time interval (step S15). ). If the clients in the areas 106 and 112 can receive the distributed data (step S16), the communication ends and waits (step S20). If they cannot be received (step S16), they can be received by the WAPs 102 and 111. Requests for retransmission of data frames that have not been made are made (step S17).
[0037]
In response to the retransmission request, the WAPs 102 and 111 retransmit the corresponding data frames in the buffers 108 and 114 (step S18), respectively (step S15). If there is no corresponding data frame (step S18), the server 101 is requested to retransmit the corresponding data frame (step S19). Receiving the retransmission request, the server 101 retransmits the corresponding data frame (step S13).
[0038]
As described above, in the above embodiment, the data frame transmission time interval is determined according to the number of clients that have made distribution requests. Therefore, the bandwidth occupancy rate during multicast communication can be limited, and non-distributed clients can communicate. It is possible to perform the communication without significantly degrading the communication performance.
[0039]
Furthermore, in the present embodiment, since a buffer for holding a data frame is provided in the WAP, processing can be performed between the WAP and the client in response to a client retransmission request, and the load on the server, The network load between the server and the WAP can be reduced.
[0040]
【The invention's effect】
The first effect of the present invention is that it is possible to reduce the occurrence of data frame errors during multicast communication. The reason for this is that, in a plurality of WAPs, data frame transmission time intervals are determined according to the ratio of clients requesting multicast communication, and data frames are transmitted at the respective transmission time intervals. This is because the radio wave interference can be reduced.
[0041]
The second effect of the present invention is that the load on the server and the network load between the server and the WAP can be reduced. The reason is that by holding the data frame transmitted from the server in the WAP, the WAP can retransmit the corresponding data frame held by itself in response to a retransmission request from the client. This is because the request can be processed between the WAP and the client without sending it to the server.
[0042]
A third effect of the present invention is that communication can be performed during multicast communication without much deterioration in communication performance of clients not subject to multicast communication. The reason is that each of the server and WAP determines the transmission time interval of the data frame according to the ratio of clients requesting the multicast communication, and transmits the data frame at this transmission time interval. This is because the bandwidth can be limited and efficient communication can be performed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a server / client system according to an embodiment of this invention.
FIG. 2 is a diagram illustrating an example of a calculation method of a transmission time interval of the server 101 illustrated in FIG.
FIG. 3 is a diagram illustrating an example of a method for calculating a transmission time interval of the WAP 102 illustrated in FIG. 1;
4 is a diagram illustrating a configuration of a server / client system in which a server 101, a WAP 102, and a client 201 in an area 106 illustrated in FIG. 1 are extracted.
FIG. 5 is a flowchart showing an operation when performing multicast communication of the server / client system according to the embodiment of the present invention.
[Explanation of symbols]
101 server 102, 111 WAP
103, 106, 112 Client area 104 Wired line 105, 107, 113 Client registration table 108, 114 Buffer 200-203, 300-302 Client

Claims (4)

A broadcast communication method in a server-client system using a wireless LAN including a server, an access point provided for the server, and a client provided for the access point, wherein the server performs multicast communication When transmitting, a data frame is transmitted to the access point at a transmission time interval according to a ratio between the number of clients belonging to the server that has made a multicast distribution request and the number of all clients belonging to the server. Broadcast communication method. The access point has made the multicast distribution request at a transmission time interval according to a ratio between the number of clients belonging to the access point that has made the multicast distribution request and the number of all clients belonging to the access point. 2. The broadcast communication system according to claim 1, wherein the data frame from the server is transmitted to a client belonging to a point. The access point includes holding means for holding the data frame from the server, and a client belonging to the access point that has made the multicast distribution request can receive at least one of the data frames from the access point. If the first retransmission request is made to resend the corresponding data frame to the client, the corresponding data frame held in the holding unit is sent to the client that has made the first retransmission request. 3. The broadcast communication system according to claim 2, wherein retransmission is performed. When the access point receives the first retransmission request and does not hold the corresponding data frame in the holding unit, the access point makes a retransmission request to the server to retransmit the corresponding data frame, and receives the request. 4. The broadcast communication system according to claim 3, wherein the server retransmits the data frame to the client that has made the first retransmission request via the access point.

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