JP2008288740A - Data communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data communication method capable of detecting the generation of communication abnormality in the case of performing communication by connecting one server with a plurality of clients and capable of controlling restoration from an abnormal state to a stable state of communication in a CSMA/CA wireless network to be often used for a conventional wireless LAN. <P>SOLUTION: The data communication method comprises: a window information analysis step S12 for analyzing window information for controlling a TCP/IP window flow which is reported from a client to a server; an abnormality detection step S13 for judging whether abnormality is generated in a transmission line or not by using the analytical value obtained by the window information analysis step S12; and a data packet transmission control step S14 for controlling the transmission of a data packet from the server to the client in accordance with a network transmission state when abnormality is detected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a data communication method, and in particular, in a CSMA / CA wireless network, when one or more clients are connected to one server and communicate, detection of occurrence of communication abnormality in a transmission path and communication The present invention relates to a method for performing recovery control from an abnormal state to a stable state.

  In the conventional CSMA / CA method (carrier sense multiple access / collision avoidance method) wireless LAN communication, radio waves are usually not transmitted except when packets are transmitted. Therefore, transmission depends on whether a carrier wave on the transmission path is detected. Communication is performed by determining the usage status of the route, and transmitting a packet if the transmission path is free, and canceling the transmission if the transmission route is not available.

  The CSMA / CA and TCP / IP protocols are bandwidth sharing networks, and are best effort (maximum effort) networks in which communication is always performed using the maximum bandwidth regardless of the type of data.

  Therefore, any communication by any device is treated as equivalent without distinction, and shares a bandwidth on the same network.

  Therefore, in such a network, if any problem occurs in data communication of a highly important connection, the transmission resource is optimized with another less important connection, and a connection with a higher importance is obtained. Control for securing transmission resources for stable communication is not performed.

  This is due to the fact that the IP network uses one shared band at best effort regardless of the data type of application or communication.

  In view of this point, as described above, as a control method that enables optimization of transmission resources according to the importance of connections and securing of transmission resources, each client in the local network collects bandwidth information of its own terminal. And transmitting it to all other clients, and each client holds the received bandwidth information of other clients together with the bandwidth information of its own terminal.

  As a result, the generated bandwidth information in the network is grasped, and each client uses the bandwidth information of the other clients and the bandwidth information of the own client to determine the numerical value of the bandwidth of the network at that time. Or the breakdown of the amount of bandwidth (for example, the ratio between the communication whose communication quality should be guaranteed and the communication which does not guarantee the quality and uses the available bandwidth).

  Each network can control the bandwidth of data to be transmitted based on the grasped bandwidth of the network. (See Patent Document 1)

  As another control method, there is a connection time division multiple access method. In this connection time division multiple access method, one transmission path is time-divided into units called time slots, and the transmission right to each time slot is controlled.

  In this control method, a method that periodically assigns time slots for each connection (TDMA), a method that randomly transmits to each time slot (slot Aloha), and a data transmission that is required for each connection There are a system that reserves a time slot and transmits the allocated time slot, and a system that combines these three systems.

  Japanese Patent No. 3003580 discloses a communication system that is an extension of the above time division multiple access system. In the case of an access method that causes collisions between data, in order to avoid an increase in traffic, transmission restrictions based on the window size in logical link control are important. Use an access method that does not cause collisions, such as the slot reservation method. If so, it is more efficient to use a larger window size.

Taking this into consideration, the data communication system that can improve the transmission efficiency while flexibly adapting to traffic fluctuations by changing the window size of the logical link control unit according to the characteristics of the line access control unit It is something that provides. (See Patent Document 2)
JP 2005-51811 A Japanese Patent No. 3003580

  However, in the above conventional method, it is necessary to introduce the same control method for all connected clients, and the server and client for synchronizing and assigning the communication timing to both the server and the client. The client had to introduce the same control method.

  This is a configuration of the prior art when communicating with an unspecified number of various clients in a network configuration that does not have a control point in addition to a transmission / reception terminal in the CSMA / CA scheme such as wireless ad hoc communication. It had a problem that it could not be realized.

  The present invention has been made to solve the above-described conventional problems. Even when the CSMA / CA method that is widely used in the conventional wireless LAN is used, detection of the occurrence of communication abnormality and stable operation from the abnormal state of communication are achieved. An object of the present invention is to provide a data communication method capable of recovery control to a state.

  In order to solve the conventional problem, a data communication method according to claim 1 of the present invention includes a server capable of continuously transmitting data packets to the client in response to a data transmission request from the client; A communication system having a plurality of clients connected to the server and performing communication, and performing communication by TCP / IP using a wireless LAN of a CSMA / CA (Carrier Sense Multiple Access / Collision Avidance) method, A data communication method for controlling data packet transmission to the client by the server, wherein a window size information solution for analyzing window size information for TCP / IP window flow control notified from the client to the server An abnormality detection step for determining the occurrence of an abnormality in the transmission line using the analysis value obtained in the step, the window size information analysis step, and when the occurrence of an abnormality in the transmission line is detected in the abnormality detection step And a data packet transmission control step for controlling the transmission of the data packet from the server to the client in accordance with a transmission state of the network.

  The data communication method according to claim 2 of the present invention is the data communication method, wherein the window size information analyzing step is configured such that when the server continuously receives notification of the maximum window size from the client, the maximum window size is determined. The maximum window continuous notification time, which is the time for which the value of is continuously notified, is output as the analysis value.

  According to a third aspect of the present invention, in the data communication method, in the data communication method, the abnormality detecting step may be configured such that the reception buffer size of the client is M bytes, and the data consumption per second of the client is D bytes. If the maximum window continuous notification time output by the window size information analysis step is Tn seconds, it is determined that an abnormality has occurred in the transmission path when M is equal to or less than D × Tn. To do.

  According to a fourth aspect of the present invention, in the data communication method, in the data communication method, when the server receives a notification of the maximum window size from the client, the window size notification immediately before that is received. The maximum window notification interval time, which is the time between the time and the maximum window size notification time, is output as the analysis value.

  In the data communication method according to claim 5 of the present invention, in the data communication method, the abnormality detecting step may be configured such that the reception buffer size of the client is M bytes, and the data consumption per second of the client is D bytes. When the maximum window notification interval time output by the window size information analysis step is Td seconds, it is determined that an abnormality has occurred in the transmission path when M is equal to or less than D × Td. To do.

  The data communication method according to claim 6 of the present invention is the data communication method, wherein the transmission control at the time of detecting an abnormality on the transmission path in the data packet transmission control step is a data packet length transmitted from the server to the client. It is characterized by changing.

  The data communication method according to claim 7 of the present invention is the data communication method according to claim 7, wherein transmission control at the time of detecting an abnormality on the transmission path in the data packet transmission control step is data packet transmission transmitted from the server to the client. The interval is changed.

  The data communication method according to claim 8 of the present invention is the data communication method, wherein the transmission control at the time of detecting an abnormality on the transmission path in the data packet transmission control step is a data packet length transmitted from the server to the client. And changing the data packet transmission interval.

  A data communication method according to a ninth aspect of the present invention is the data communication method according to the data communication method, wherein the transmission control at the time of detecting an abnormality on the transmission path in the data packet transmission control step is performed from the server to the client by UDP (User Datagram Protocol). And transmitting a data packet.

  According to the data communication method of the present invention, a window size information analyzing step for analyzing window size information for TCP / IP window flow control notified from a client to a server, and an analysis value obtained in the window size information analyzing step And an abnormality detection step for determining the occurrence of an abnormality in the transmission line, and when the occurrence of an abnormality in the transmission line is detected in the abnormality detection step, control of transmission of a data packet from the server to the client The data packet transmission control step is performed according to the transmission state of the network, so that the server side uses the TCP / IP window size notified from the client without implementing a special mechanism on the client side. Detecting communication errors on the network By changing the data packet transmission method to the client in which the communication abnormality is detected, the transmission of the data packet is controlled only for a specific connection in the same transmission path, and the communication abnormal state is changed to the stable state. Recovery can be done.

Embodiments of the data communication method of the present invention will be described below in detail with reference to the drawings.
(Embodiment 1)
FIG. 1 shows a configuration of a radio communication system according to Embodiment 1 of the present invention.

  The wireless communication system according to the first embodiment shown in FIG. 1 is constructed by a wireless LAN of CSMA / CA (Carrier Sense Multiple Access / Collision Avidance) method, uses a TCP / IP communication protocol, and uses an AV video. The data packet for streaming playback is communicated.

  The server 1 has a function of receiving data transmission requests from the client 2, the client 3, and the client 4 and continuously transmitting data packets to the clients 2, 3, and 4. 4 has a function of determining window size information according to the free state of its own communication buffer and notifying the server 1 of the window size information.

  The window size of the window size information represents how much data each receiving side can currently receive, and is determined by the free capacity in the receiving buffer of each receiving side. Each receiving side notifies the window size to the transmitting side, so that the transmitting side can know the receivable data capacity of each receiving side, and based on the notified window size, the transmission data to each client Determine the amount and send.

  If the reception buffer of the client is empty, the window size information is large. Conversely, if the reception buffer is full, the window size information is notified to be small, and the server 1 is notified from each of the clients 2, 3, and 4. Data communication flow control is performed such that data corresponding to the window size information is transmitted to the clients 2, 3, and 4.

  FIG. 2 shows a flow chart of a method for detecting a communication error on the network and controlling the transmission of the data packet using the TCP / IP window size in the first embodiment of the present invention. Below, the flowchart of FIG. 2 is demonstrated.

  First, in step S11, the server receives window size information from the client.

  In the next step S12, the window size information received from the client is monitored and analyzed.

  In the next step S13, it is determined whether an abnormality has occurred in communication based on the analysis value of the window size information obtained in step S12.

  If an abnormality has occurred in step S13, in the next step S14, transmission control of data packets from the server to the client is performed according to the transmission state of the network.

  In step S14, the data packet transmission control is performed, and the data packet transmitted is transmitted from the server to the client in the next step S15, and an attempt is made to return from a communication abnormal state to a stable communication state.

Hereinafter, the details of the above steps will be described.
In step S11, a data transmission request notified from the client is received, and window size information is acquired from the received data. Since the window size information is described in the TCP header in the packet in communication using the TCP / IP protocol, this value is used. On the client side, no special implementation is required to acquire the window size, and acquisition of the window size can be realized using a conventional communication protocol.

  In step S12, window size information is monitored and the information is analyzed. FIG. 3 shows changes over time in the window size notified from the client to the server.

  In FIG. 3, W-1 is a window size transition line (W-1) in a normal state showing an example of a temporal change in the window size in a state where AV video streaming reproduction is normally performed.

  If data communication is normally performed, the window size is repeatedly increased and decreased over time and changes.

  This is because if the amount of data supplied from the server exceeds the amount of data consumed by playback at the client, the data capacity in the buffer will increase, so the window size notified by the client to the server will be reduced, and This is because, if the amount of consumed data exceeds the amount of supplied data, the client increases the window size and increases the amount of supplied data from the server.

  On the other hand, W-2 is a window size transition line (W-2) in an abnormal state showing an example of transition of the window size when a problem occurs in communication.

  In the window size transition line (W-2) in the abnormal state, the value of the window size transitions at the maximum value on the way. Since the value of the maximum window size is a value defined by the TCP / IP standard, it is not always equal to the reception buffer size, but is usually smaller than the reception buffer.

  When a problem such as packet loss due to delay or failure occurs on the transmission path and the data packet from the server is difficult to reach the client, the data consumption in the client's receive buffer greatly exceeds the data supply amount And the data capacity in the buffer will continue to decrease.

  In this case, there will be space in the buffer that is larger than the maximum window size that can be set, and the amount of data in the buffer will increase until the free space in the buffer becomes less than or equal to the maximum window size. It will continue to notify the server of the maximum window size. The continued maximum window size means that the receive buffer is in a depleted state.

  In step S12, the length of time during which the maximum window size notified from the client continues is monitored. That is, in step S12, when the notification of the maximum window size is received, the time Tn seconds in which the notification of the maximum window size continues from that time is measured, and the value of Tn is used as the analysis value for the determination in step S13.

  In the next step S13, the occurrence of an abnormality in the transmission path is determined using the analysis value Tn of the time when the notification of the maximum window size obtained in step S12 continues.

  Assume that the client receive buffer size is M bytes, the client data consumption per second is D bytes, and the data amount in the communication buffer continues to decrease while the maximum window size notification continues. , “D × Tn ≧ M”, it can be estimated that the data in the buffer is approaching a depleted state, and it can be determined that an abnormality has occurred in the transmission path. At this time, as the value of D, the bit rate of the AV moving image data to be transmitted may be used, or the data transfer rate during normal communication may be measured in advance and used.

  As for the value of M, when the buffer size on the client side is unknown, a commonly used TCP communication buffer size, for example, 24 Kbytes may be used, or the amount of data requested by the client from the server to the client in advance. More data packets may be transmitted excessively, and a value estimated from the cumulative amount of excessive transmitted packets may be used until the window size returned from the client becomes zero.

In step S13, the occurrence of abnormality may be detected as follows.
First, in step S12, when the notification of the maximum window size is received from the client, the time Td seconds between the notification time and the immediately preceding window size information notification time is measured, and this Td second is analyzed. Calculate as

  In the next step S13, the occurrence of an abnormality in the transmission path is determined using the analysis value Td obtained in step S12. During Td seconds, data in the reception buffer of the client continues to be consumed. By “D × Td ≧ M”, it can be estimated that the data in the buffer is approaching a depleted state. It is possible to determine that an abnormality has occurred.

  In step S14, when it is determined in step S13 that an abnormality has occurred, transmission control of data packets is performed so that data requested by the client can be stably transmitted. This data packet transmission control method is shown in the flowchart of FIG.

  In FIG. 4, when the occurrence of an abnormality is detected in step S13, the server increases the packet length of the data packet to be transmitted to the client in step S21 in order to promote communication stabilization. Here, as the increase amount of the packet, an appropriate value may be selected depending on the amount of data to be communicated and the communication content. For example, the packet length can be increased by 10% of the maximum window size and transmitted to the client.

  In step S22, the server transmits a data packet to the client, and the client that has received the data packet notifies the server of window size information that has changed due to the reception of the data packet.

  In step S23, the server that has received the response of the window size information determines the value of the window size. If the window size is not smaller than the maximum window size, the process returns to step S21 to further increase the data packet length and perform packet transmission.

  If the window size has decreased from the maximum window size in step S23, it is determined in step S24 whether the window size is 0. If not, the data packet length remains unchanged and the process returns to step S22. , Send a data packet to the client.

  If the window size is 0 in step S24, it means that an excessive data packet is received by the client, so the process proceeds to step S25, and the data packet transmission method is returned to the normal method.

  Here, in the wireless LAN communication of the CSMA / CA system, since the packet is transmitted if the transmission path is vacant and the transmission is canceled if the transmission path is not vacant, the data packet transmission is first-come-first-served. .

  However, by increasing the data packet length in step S21 and transmitting, the amount of data per packet can be increased even if the probability of securing the transmission path is the same. Therefore, it is possible to secure a bandwidth necessary for the stable operation of the client.

  As another suitable data packet transmission control method, in step S21, the packet length may be shortened and the packet transmission interval may be shortened. In such a method, the communication is similarly abnormally performed. Can be recovered from.

  For example, when the packet length is halved, a method of transmitting two packets by halving the packet transmission interval can be used.

  By shortening the packet transmission interval in this way, it is possible to increase the probability of securing a transmission path for packet transmission, and in the case of communication abnormality such as packet loss, more data reaches the client. It is possible to increase the probability of making it happen.

  Similarly, by shortening only the packet transmission interval without changing the packet length, it is possible to increase the probability of securing a transmission path in packet transmission and to recover communication from an abnormal state.

  Furthermore, as another suitable data packet transmission control method, the packet transmission method in step S21 may be changed to the transmission by the UDP (User Datagram Protocol) method, and the communication is changed from the abnormal state as described above. It can be recovered and is described below.

  The UDP communication is a connectionless communication method and is an unreliable communication method because even if the server transmits data to the client, data reception confirmation from the client side is not performed.

  However, in this UDP communication, data is transmitted from the server to the client without waiting for a response from the client side, so that high-speed data transfer is possible. It is possible to control the data transmission method during

  This UDP communication is not reliable but is capable of high-speed communication, so it can be said that it is an effective method for communication in which some communication errors do not pose a problem, such as AV video streaming communication. Is.

  Also, when performing UDP communication, the data packet length and the data packet transmission interval can be changed.

  According to the data communication method of the first embodiment as described above, in response to a data transmission request from a client, a server capable of continuously transmitting data packets to the client is connected to the server. In the communication system that performs communication by TCP / IP using a CSMA / CA wireless LAN, the server controls data packet transmission from the server to the client. In the data communication method, a window information analysis step for analyzing window information for TCP / IP window flow control notified from the client to the server, and an analysis value obtained in the window information analysis step, An anomaly detection step for determining the occurrence of an anomaly in the transmission line; A data packet transmission control step for controlling transmission of a data packet from the server to the client in accordance with a transmission state of the network when an abnormality in the transmission path is detected in the abnormality detection step. Therefore, without implementing a special mechanism on the client side, the server side detects a communication error on the network using the TCP / IP window size notified from the client, and the client in which the communication error is detected is detected. By changing the transmission method of the data packet to the network, it is possible to control the transmission of the data packet only to a specific connection in the same transmission path and recover from the abnormal communication state to the stable state.

  The data communication method according to the present invention uses the TCP / IP window size notified from the client to the server, detects a communication abnormality on the network, and controls the transmission of the data packet from the server side. This makes it possible to perform transmission control only for a specific connection in the same transmission path without implementing a special mechanism on the client side. In particular, in a CSMA / CA wireless network, This is useful as a method for detecting the occurrence of a communication abnormality in a transmission line when one or more clients are connected to the server, and for performing recovery control from a communication abnormal state to a stable state.

1 is a configuration diagram of a wireless communication system that implements a data communication method according to Embodiment 1 of the present invention. Flow chart of data packet transmission control method in Embodiment 1 of the present invention The graph which shows the time change of the window size in Embodiment 1 of this invention FIG. 4 is a partial flowchart of the data packet transmission control method according to the first embodiment of the present invention.

Explanation of symbols

1 server 2, 3, 4 client S11 step of receiving window size information S12 step of analyzing window size information S13 step of determining whether or not an abnormality has occurred in communication S14 step of performing transmission control of data packet S15 data Step S21 for transmitting a packet Step S21 for increasing the packet length S22 Step for transmitting a data packet S23 Reception of window size information and step for checking whether the window size is decreasing S24 Step for checking whether the window size is zero Step S25 Step for performing normal packet transmission control W-1 Window size transition line in normal state W-2 Window size transition line in abnormal state

Claims (9)

In response to a data transmission request from a client, the server has a server capable of continuously transmitting data packets to the client, and a plurality of clients connected to the server for communication. In a communication system that performs communication by TCP / IP using a wireless LAN of a Sense Multiple Access / Collision Avidity) method, a data communication method in which data transmission from the server to the client is controlled by the server,
A window size information analyzing step for analyzing window size information for TCP / IP window flow control notified from the client to the server;
Using the analysis value obtained in the window size information analysis step, an abnormality detection step for determining the occurrence of an abnormality in the transmission line,
A data packet transmission control step for controlling the transmission of data packets from the server to the client when the occurrence of an abnormality in the transmission path is detected in the abnormality detection step;
A data communication method characterized by the above. The data communication method according to claim 1,
In the window size information analysis step, when the server continuously receives a notification of the maximum window size from the client, a maximum window continuous notification time, which is a time for which the value of the maximum window size is continuously notified, Output as the analysis value,
A data communication method characterized by the above. The data communication method according to claim 2,
In the abnormality detection step, the reception buffer size of the client is M bytes, the data consumption per second of the client is D bytes, and the maximum window continuous notification time output by the window size information analysis step is Tn. When M is equal to or less than D × Tn, it is determined that an abnormality has occurred in the transmission path.
A data communication method characterized by the above. The data communication method according to claim 1,
In the window size information analysis step, when the server receives a notification of the maximum window size from the client, a maximum window notification that is a time between the window size notification time immediately before and the maximum window size notification time. The interval time is output as the analysis value.
A data communication method characterized by the above. The data communication method according to claim 4, wherein
In the abnormality detection step, the reception buffer size of the client is M bytes, the data consumption per second of the client is D bytes, and the maximum window notification interval time output by the window size information analysis step is Td. When M is equal to or less than D × Td, it is determined that an abnormality has occurred in the transmission path.
A data communication method characterized by the above. The data communication method according to any one of claims 1 to 5,
The transmission control at the time of abnormality detection on the transmission path in the data packet transmission control step changes a data packet length transmitted from the server to the client.
A data communication method characterized by the above. The data communication method according to any one of claims 1 to 5,
The transmission control at the time of abnormality detection on the transmission path in the data packet transmission control step changes a data packet transmission interval transmitted from the server to the client.
A data communication method characterized by the above. The data communication method according to any one of claims 1 to 5,
The transmission control at the time of detecting an abnormality on the transmission path in the data packet transmission control step changes a data packet length transmitted from the server to the client, and a data packet transmission interval.
A data communication method characterized by the above. The data communication method according to any one of claims 1 to 5,
The transmission control at the time of detecting an abnormality on the transmission path in the data packet transmission control step transmits a data packet from the server to the client by UDP (User Datagram Protocol).
A data communication method characterized by the above.

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