JP5099457B2 - Communication method and control device - Google Patents

Description

  The present invention relates to random access communication.

  As a standard for random access, there is CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) adopted in IEEE802.11 of wireless LAN (Local Area Network). CSMA / CA has an algorithm called “backoff” for avoiding signal collision.

  In the back-off procedure, for example, in the case of a wireless LAN, all terminals that intend to transmit a frame of a wireless signal generate a random number corresponding to the number of slots in the standby time at a common timing. Then, transmission is waited for the number of slots indicated by the random value. Therefore, a terminal having a smaller random value has a shorter transmission standby time, and therefore can obtain a transmission right earlier.

  In the back-off procedure described above, each terminal recognizes that the transmission frame has arrived safely by receiving a response frame from a device (for example, an access point) that has received the frame transmitted by itself. If the response frame cannot be received within the specified time, it is assumed that the transmission frame has been lost and the frame is retransmitted. At that time, the terminal performs the above-described back-off operation again, and performs retransmission after a standby time based on the random number generated there.

A minimum value and a maximum value are set for the random numbers used by the terminal for back-off, and the maximum value is called a CW (Contention Window). Here, when the CW of the previous transmission and CW _0, CW at the time of retransmission is added value to 1 to 2 times the _{CW 0 (CW = 2 × CW} 0 +1) is applied. Then, for each further retransmission, the current CW is replaced with CW _0, the CW ₀ is applied to the calculation of a new CW.

  Incidentally, in recent years, wireless LANs are used for multimedia communications such as voice calls and video distribution. Communication quality (QoS) required for multimedia communication varies depending on applications such as voice and video. According to the back-off algorithm described above, since a random number is used, the right to transmit is given fairly to all terminals. However, in the case of an application that is required to obtain a transmission right earlier, in order to guarantee QoS, it is necessary to differentiate the transmission right of the terminal from those of other terminals.

  As a technique related to the transmission right, for example, there is one described in Patent Document 1 described later. The method described in this document is such that a node requiring emergency transmission deprives other nodes of transmission rights in a LAN employing CSMA / CD (Carrier Sense Multiple Access with Collision Detection). A node requiring emergency transmission transmits a collision signal (jam signal) for a longer period than other nodes, or repeatedly transmits a collision signal. Thus, the emergency data of the own node is transmitted while the other node performs the back-off.

JP-A-11-355324

  According to the method described in Patent Document 1, a terminal that requires emergency transmission can obtain a transmission right earlier. However, in the above method, since the collision signal is controlled in units of terminals, it is assumed that when the number of terminals to be urgently transmitted increases, a contention for transmission rights occurs between these terminals. In this case, in the network, the occupancy of the line due to the collision signal is increased, so that the urgency of data may be greatly impaired.

  The objective of this invention is providing the communication method and control apparatus which control so that the transmission right between terminals may be differentiated appropriately.

  The communication method according to the present invention uses a step of capturing a data signal in communication by CSMA / CA and information possessed by the data signal whether or not to transmit a collision signal for prompting retransmission of the captured data signal. And the step of transmitting the collision signal to the same communication channel as the communication channel of the captured data signal when it is determined to transmit the collision signal.

  The control apparatus according to the present invention includes a receiving unit that captures a data signal in communication by CSMA / CA, and information that the data signal includes whether to transmit a collision signal for prompting retransmission of the captured data signal. And a control unit that determines whether to transmit the collision signal, and a transmission unit that transmits the collision signal to the same communication channel as the communication channel of the captured data signal.

  ADVANTAGE OF THE INVENTION According to this invention, it can control to differentiate appropriately the transmission right between terminals in communication by CSMA / CA.

It is a block diagram of the system in the 1st Example of this invention. It is a block diagram of the control device in the 1st example of the present invention. It is a block diagram of the collision signal control part in 1st Example of this invention. It is a flowchart which shows operation | movement of the control apparatus in 1st Example of this invention. It is a block diagram of the system in the 2nd Example of this invention. It is a block diagram of the collision signal control part in 2nd Example of this invention. It is a flowchart which shows operation | movement of the control apparatus in 2nd Example of this invention. It is a block diagram of the collision signal control part in the 3rd example of the present invention. It is a flowchart which shows operation | movement of the control apparatus in 3rd Example of this invention.

Explanation of symbols

100 wireless LAN system
101 wireless LAN base station
102 Wireless LAN terminal (high priority)
103 Wireless LAN terminal (low priority)
104 Controller

<First embodiment>
FIG. 1 is a block diagram of a system in the first embodiment of the present invention. The system 100 according to the present embodiment is a wireless LAN compliant with IEEE 802.11, and adopts a random access method based on CSMA / CA. As shown in FIG. 1, the system 100 includes a wireless LAN base station 101, wireless LAN terminals 102 and 103, and a control device 104.

  In this embodiment, a terminal that guarantees a predetermined QoS is a wireless LAN terminal 102 (high priority), and the transmission right of this wireless LAN terminal 102 is differentiated from that of the other wireless LAN terminal 103 (low priority). It is assumed that The predetermined QoS referred to here is, for example, QoS required to obtain a transmission right earlier in a wireless LAN, such as emergency call from a mobile phone.

  The control device 104 responsible for transmission right control as described above is arranged in the communication area of the wireless LAN base station 101 in the system 100. In this communication area, a wireless frame communicated between the wireless LAN base station 101 and each terminal (102, 103) is captured.

  FIG. 2 shows the configuration of the control device 104. The control device 104 includes a wireless LAN communication unit 202 including a transmission unit 203 and a reception unit 204, and a control unit 201. The receiving unit 204 captures a frame that propagates through the wireless LAN. The control unit 201 determines whether or not to transmit a collision signal using information held in the captured frame. The transmission unit 203 transmits a collision signal to the wireless LAN.

  FIG. 3 shows the configuration of the control unit 201 described above. The frame analysis unit 206 analyzes the MAC header of the frame captured by the reception unit 204 by the MAC header analysis unit 206a, and detects information on the transmission source, the frame type, and the like from the MAC header.

  The determination unit 207 determines whether or not to transmit a collision signal using information detected from the MAC header of the frame. The collision signal is transmitted to the same channel as the communication channel of the current frame. As a result, the collision signal collides with the radio frame being propagated, and the propagation of the frame is interrupted.

  The target of collision in the present embodiment is a data frame as a data signal transmitted from the terminal to the base station 101. When the propagation of the data frame is interrupted, the transmission source of the frame cannot receive the ACK from the base station 101. Thus, the transmission of the collision signal can prompt the transmission source to retransmit the frame.

  When it is determined that a collision signal is transmitted, the collision signal generation unit 208 generates a collision signal. The transmission unit 203 transmits the generated collision signal to the same channel as the channel in which the current frame is captured. In this embodiment, a collision signal is transmitted before all of the frames captured this time reach the wireless LAN base station 101.

  The operation of the control device 104 will be described along the flowchart shown in FIG. In the control device 104, first, when the receiving unit 204 receives a radio frame (step F101), the MAC header analyzing unit 206a analyzes the MAC header of the frame and detects information such as a transmission source address and a frame type (step). F102).

  The determining unit 207 determines whether or not the current frame is a frame that has been retransmitted N times or more (N ≧ 1) from the detected information (step F107). Whether or not a frame is due to retransmission can be determined by recording information such as the transmission source and frame number of the frame every time a frame is received. In this case, a frame in which a match with the recorded information is detected is recognized as a retransmission frame. Then, by counting the number of times of such recognition, it can be determined whether the number of retransmissions has reached N times.

  When the current frame is not due to retransmission (step F107: NO), the determination unit 207 determines whether the transmission source of the frame is a collision target (step F103). The collision target refers to a terminal other than a terminal that guarantees a predetermined QoS. In this embodiment, the wireless LAN terminal 103 (low priority) in FIG. 1 corresponds to the collision target.

  In order to determine the collision target, the control device 104 registers in advance the address of a terminal that requires QoS guarantee, such as the wireless LAN terminal 102 (high priority), and selects a source terminal that does not correspond to the address. Recognize as a collision target. Conversely, the address of a terminal subject to collision, such as the wireless LAN terminal 103 (low priority), may be registered in advance. In this case, when the transmission source of the received frame corresponds to the registered address, the received frame is determined as a collision target.

  When the transmission source of the frame is a terminal that does not correspond to the collision target (step F103: NO), the determination unit 207 determines that the collision signal is not transmitted (step F001), and checks the newly captured frame. Move.

  When the transmission source of the frame corresponds to the collision target (step F103: YES), the determination unit 207 determines whether or not the frame is a data frame (step F104). The data frame here refers to a frame that does not correspond to a frame for controlling or managing wireless LAN communication, for example, a frame for transmitting audio, video, or a document. When the frame is not a data frame (step F104: NO), the determination unit 207 determines that a collision signal is not transmitted (step F001).

  On the other hand, when the frame is a data frame transmitted from a collision target terminal (step F104: YES), the determination unit 207 determines to transmit a collision signal (step F002).

  When the transmission of the collision signal is determined, the collision signal generation unit 208 generates a collision signal (step F105). The size of the collision signal may be calculated by the determination unit 207. In this case, for example, the determination unit 207 recognizes a busy time, that is, a frame transmission period, from the Duration / ID field of the MAC header, and calculates a signal size that can interrupt frame propagation during that period. That's fine.

  The collision signal generation unit 208 instructs the transmission unit 203 to transmit a collision signal before the end of the frame propagation period in order to prevent the current frame from being completely received by the base station 101. The transmission unit 203 transmits a collision signal in accordance with this instruction (step F106).

  When the frame captured this time has been retransmitted N times or more (step F107: YES), the determination unit 207 determines that a collision signal is not transmitted (step F001). This is a measure for preventing the transmission right of a terminal from being remarkably lowered due to repeated retransmissions even if the terminal has a low priority. The threshold value N is desirably set to a value suitable for such measures. Further, the threshold value N is not limited to a fixed value, and may be appropriately changed according to the number of terminals that the control device 104 grasps at the present time and the congestion status of the line. In addition, when the above measures are not necessary, the step (F107) may be omitted.

  Here, the overall operation of the system when a collision signal is transmitted in the present embodiment will be described with reference to the system configuration of FIG.

  The situation illustrated in FIG. 1 is a situation in which the control device 104 recognizes the wireless LAN terminal 103 (low priority) as a collision target and transmits a collision signal to the data frame transmitted by the wireless LAN terminal 103. On the other hand, the wireless LAN terminal 102 (high priority) for which QoS is guaranteed is not determined as a collision target by the control device 104. Therefore, all the frames transmitted from the wireless LAN terminal 102 reach the wireless LAN base station 101. Accordingly, the wireless LAN terminal 102 receives a response frame (hereinafter referred to as “ACK”) from the wireless LAN base station 101.

  The wireless LAN terminal 103 subject to collision cannot receive ACK for the data frame from the base station 101 because the transmitted data frame is invalidated by the collision signal. The wireless LAN terminal 103 recognizes that the data frame is lost during transmission, and retransmits the frame according to the back-off procedure.

The wireless LAN terminal 103 newly generates a random number in order to measure the retransmission timing. Here, as described above, the upper limit CW of the random number increases for each retransmission (CW = 2 × CW ₀ +1). Therefore, the probability of generating a larger random value increases as the number of retransmission opportunities increases. As the random value increases, the retransmission standby time becomes longer, and therefore the priority of the transmission right tends to decrease.

  Specifically, for example, in the case of IEEE802.11b, the upper limit CW of the random number starts from “31”, and “63”, “127”, “255”,. It increases in order. This is because the range of random numbers is “0” to “31” at the first transmission, whereas “0” to “63” at the first retransmission, and “0” to “127” at the second retransmission. ". Therefore, as the number of retransmissions increases, the priority of the transmission right decreases stochastically.

  Using this action, the control device 104 treats a terminal other than the wireless LAN terminal 102 that requires QoS guarantee, that is, the wireless LAN terminal 103 (low priority) as a collision target. Then, the frame transmission from the wireless LAN terminal 103 to the base station 101 is interrupted by the collision signal, thereby prompting the terminal 103 to retransmit.

  According to the present embodiment, the right to transmit radio frames between terminals can be appropriately differentiated. Thereby, it is possible to guarantee the QoS of an application that is required to obtain a transmission right earlier. In addition, since it is determined based on the regulation whether or not a collision signal is transmitted, it is possible to prevent line congestion due to frequent collision signals.

<Second embodiment>
A second embodiment of the present invention will be described. The difference between this embodiment and the first embodiment described above lies in the target of the collision signal. The target of the collision signal in the present embodiment is an ACK returned from the base station 101 in response to a radio frame transmitted by the collision target terminal.

  FIG. 5 shows the system configuration of the second embodiment of the present invention. The configuration of the system 200 of this embodiment is the same as that of the first embodiment (FIG. 1) described above. The situation shown in FIG. 5 is that the control device 104 responds to the ACK transmitted from the base station 101 to the wireless LAN terminal 103 after the data frame from the wireless LAN terminal 103 as the collision target reaches the wireless LAN base station 101. Is a situation where a collision signal is transmitted.

  In the above-described embodiment (FIG. 1), transmission of ACK from the base station 101 is prevented by interrupting frame transmission from the collision target terminal (103) to the base station 101. In contrast, the present embodiment prevents an ACK from the base station 101 for the collision target terminal (103) from reaching the terminal.

  FIG. 6 shows a configuration of the control unit 201 in the control device 104 of the present embodiment. The control unit 201 of the present embodiment is equivalent to the control unit 201 to which the FCS (Frame Check Sequence) analysis unit 206b of the frame analysis unit 206 and the timer unit 210 are added to those of the above-described embodiment (FIG. 3). .

  The FCS analysis unit 206b uses the FCS value following the data field of the frame captured by the reception unit 204 to analyze whether or not the size of the frame is appropriate. As a result of the analysis, a frame whose size is not appropriate, such as shorter than the size based on the FCS value, is regarded as an error frame by the determination unit 207.

  The timer unit 502 acquires the frame reception time from the reception unit 204, and starts counting from that time. Further, the busy time of the Duration / ID field of the MAC header is acquired from the determination unit 207, and the propagation time of ACK for the current frame is calculated based on the busy time and the above reception time.

  The operation of the control device 104 of the present embodiment will be described along the flowchart shown in FIG. In the control device 104, first, when the reception unit 204 receives a radio frame (step F201), the timer unit 210 starts counting from the frame reception time.

  The MAC header analysis unit 206a analyzes the MAC header of the received frame and detects information such as a transmission source address and a frame type. Also, the FCS analysis unit 206b checks the frame size using the FCS value of the frame (step F202).

  When it is determined from the FCS inspection result that the current frame is an error frame (step F203: YES), the determination unit 207 determines that a collision signal is not transmitted (step F001). This is because, even if the frame transmission is not interrupted by the collision signal, the base station 101 that has received this frame thereafter detects an error and does not transmit an ACK. Therefore, it is possible to prevent useless transmission of a collision signal by determining an error frame and determining that a collision signal is not transmitted.

  On the other hand, if the current frame is not an error (step F203: NO), the transmission source and frame type of the frame are inspected in the same manner as in the above-described embodiment (FIG. 4: F103, F104), and the collision signal is detected. Is determined (steps F204 and F205). Although omitted in the flowchart of FIG. 7, the determination based on the number of retransmissions of frames (FIG. 4: F107) described in the above embodiment may be added to the determination of the transmission of the collision signal.

  When it is determined that a collision signal is to be transmitted (step F002), the collision signal generation unit 208 generates a collision signal (step F206). The timer unit 210 also calculates the propagation time of ACK for the current frame. Then, based on the calculation result, the collision signal generation timing is notified to the collision signal generation timing, that is, the timing at which the ACK from the base station 101 is interrupted (step F207).

  The collision signal generation unit 208 waits until the timing notified from the timer unit 210, and when the timing arrives, instructs the transmission unit 203 to transmit a collision signal (step F208).

  When propagation of ACK is interrupted by a collision signal transmitted from the transmission unit 203, the terminal that is the destination of the ACK cannot receive ACK. Thereby, it recognizes that the frame transmitted by itself has been lost, and moves to preparation for retransmission by backoff.

  As described above, even when ACK from the base station 101 to the terminal is used as a collision target, it is possible to prompt the terminal to retransmit the frame. Therefore, the right to transmit radio frames between terminals can be appropriately differentiated. Further, according to the present embodiment, it is only necessary to prepare a collision signal before an ACK is transmitted from the base station 101. Therefore, there is an advantage that it is easy to aim at the target of the collision.

<Third embodiment>
A third embodiment of the present invention will be described. In this embodiment, a criterion for determining the transmission of a collision signal is determined according to the communication status of the wireless LAN. The system configuration of this embodiment is the same as that of the above-described embodiment shown in FIG. 1 or FIG. The criteria determined in the present embodiment can be combined with the above-described embodiments. In the following description, for the sake of convenience, the case of combining with the first embodiment is assumed.

  FIG. 8 shows the configuration of the control unit 201 in the control device 104 of the present embodiment. The control unit 201 of the present embodiment is equivalent to a configuration obtained by adding a standard determination unit 211 to the configuration of the first embodiment (FIG. 3).

  The operation of the control device 104 of the present embodiment will be described along the flowchart shown in FIG. In the control device 104, the criterion determining unit 211 sequentially monitors the communication state of the wireless LAN using the frames captured by the receiving unit 204 (step F301). Then, based on the monitoring result, a determination criterion regarding the transmission of the collision signal is determined (step S302), and the determined criterion is provided to the frame analysis unit 206 and the determination unit 207.

  It should be noted that it is desirable to update the above-mentioned determination criteria periodically or at an arbitrary timing according to a change in the monitor result. This makes it possible to apply a determination criterion corresponding to the latest communication status.

  When the receiving unit 204 captures the frame (step F303), the control device 104 performs the same processing (FIG. 4: processing A) as in the first embodiment based on the criterion provided by the criterion determining unit 211. Execute (Step F304). That is, the frame analysis unit 206 analyzes the MAC header of the frame, and based on the result, the determination unit 207 determines whether to transmit a collision signal. When a collision signal is transmitted, the collision signal generation unit 208 generates the collision signal and transmits it by the transmission unit 203.

  Regarding the wireless LAN communication status, the contents monitored by the criterion determining unit 211 can be set in various ways according to the required QoS. For example, the type of traffic can be the monitor content. When the type of traffic to be monitored is a VoIP call, the criterion determining unit 211 monitors a VoIP frame among the radio frames captured by the receiving unit 204. When a VoIP frame is captured, the source address is acquired from the frame, and the determination unit 207 is instructed not to transmit a collision signal to the VoIP frame from this address. This means that the criterion has been determined that frames from the IP phone that is currently talking are not targeted for collision. Recognizing this criterion, the determination unit 207 determines that a collision signal is to be transmitted to a frame from a terminal other than the terminal that is in a call.

  The content to be monitored may be a flow. In this case, even the same terminal may not be subject to collision depending on the flow. In the flow monitoring, for example, when there are five pieces of information for identifying a flow (5 tuple), the criterion determining unit 211 determines the source IP address (source IP), the destination IP address (destination IP), and the protocol number. A flow is identified by a combination of a source TCP port number (source TCP port) and a destination TCP port number (destination TCP port).

  The criterion determination unit 211 detects a flow whose band occupancy is higher than the required band and instructs the determination unit 207 to transmit a collision signal to the flow. The determination unit 207 acquires a flow identifier (5 tuple) from the IP header or TCP header acquired by the frame analysis unit 206. When a flow having an identifier corresponding to the flow instructed by the standard determination unit 211 is detected, the flow is set as a collision target. Thereby, the occupation rate of the band by the target flow can be temporarily reduced.

  The monitor content may be a frame length. This is useful when the type of flow or traffic cannot be specified because the frame is encrypted. For example, in the case of a voice packet, the frame length is relatively short because it is smaller in size than other traffic packets. Therefore, voice traffic can be estimated from the frame length. The criterion determination unit 211 acquires the frame length from the Duration / ID field of the MAC header, and estimates the transmission state of the voice packet. Then, for example, when the transmission amount of the voice frame exceeds a certain threshold, a criterion for making the frame subject to collision is determined.

  Further, the monitor content may be a band occupation situation. In this case, the criterion determination unit 211 acquires information on the bandwidth occupancy rate in the wireless LAN from, for example, QBSS Load in the beacon frame of the wireless LAN. For example, when the bandwidth occupancy is high, that is, when the line is busy, as in the above-described embodiment, a terminal without QoS guarantee is targeted for collision, and when it is not busy, any frame is included. Also determine the criteria for not transmitting a collision signal. As a result, it is possible to create an adaptive standard that takes into account the congestion status of the line.

  The monitor contents may be the throughput of each terminal. In this case, for example, a criterion that a terminal having a higher throughput than other terminals is set as a collision target is determined.

  The monitor content may be the maximum communication speed. The maximum communication speed by IEEE802.11b is 11 Mbps, but in the case of IEEE802.11g having a different physical modulation method from this, it is 54 Mbps, and high-speed communication is possible. In this case, for example, even if a frame has a low priority, a criterion may be set such that the communication standard is not subject to collision when the IEEE 802.11g is IEEE 802.11b and is subject to collision when the IEEE 802.11b is IEEE 802.11b. Thereby, the request | requirement of the high-speed communication by IEEE802.11g can be met.

  The monitor content may be the content of a frame transmitted by the terminal. This is, for example, whether or not the content of the frame is an urgent frame such as SOS transmission. The criterion determining unit 211 determines a criterion that a collision signal is not transmitted to a frame in which such content is described regardless of the transmission source and the frame type. Thereby, the urgency of SOS transmission can be guaranteed.

  Further, the monitor content may be electric field strength, that is, radio wave reception sensitivity by the terminal. In this case, the criterion determining unit 211 monitors the electric field strength of the terminal with respect to the base station, and determines a terminal having a weak electric field strength as a collision target. As a result, it is possible to prompt a terminal with weak electric field strength to be handed over to another base station. Conversely, the criterion may be such that a terminal having a strong electric field strength is a collision target and a terminal having a low electric field strength is prioritized.

  The monitor content may be a communication error situation. For example, the status of a communication error in the wireless LAN is monitored from the FCS of the frame transmitted by each terminal or the transmission status of ACK from the base station 101. Then, for example, it is possible to set a criterion that a terminal having a large number of errors is a collision target. Conversely, the criterion may be that a terminal with few errors is a collision target and a data frame from a terminal with many errors is given priority.

  In this embodiment, the contents to be monitored are not limited to any one of the above, but may be applied in combination of two or three or more.

  According to the present embodiment, the criterion for determining whether or not to transmit a collision signal can be dynamically changed according to the communication status. This makes it easier to deal with QoS requests from terminal users and network administrators.

  In each of the above embodiments, the present invention is applied to wireless LAN communication by CSMA / CA. However, the application of the present invention is not limited to wireless, but wired as long as it is communication by CSMA / CA. Also good. For example, PLC (Power Line Communication) using a power line adopts CSMA / CA, and thus the present invention can be applied.

  As the contents of monitoring in the third embodiment, billing information may be monitored in addition to the communication status. In this case, for example, it is possible to give priority to a user terminal for which payment has been properly made by setting a user terminal for which a communication fee has not been paid as a collision target. In addition, a criterion for changing the collision rate may be set according to the charge level.

  In each of the above embodiments, the control device 104 is an independent node in the system 100. However, the control device according to the present invention is integrated with a node that receives a data signal from a terminal, such as the base station 101 described above. May be.

  The present invention is not limited to the above embodiment. The implementation of the present invention can be modified as appropriate within the scope of the claims of the present invention. For example, the present invention may be implemented as a computer program corresponding to the operation of the control device 104 in each of the above embodiments or a computer-readable recording medium storing the program.

This application claims priority based on Japanese Patent Application No. 2007-143875 filed in Japan on May 30, 2007, the entire contents of which are incorporated herein.

Claims (19)

Capturing a data signal in communication by a random access method;
Determining whether or not to transmit a collision signal for prompting retransmission of the captured data signal, using information held by the data signal;
And a step of transmitting the collision signal to the same communication channel as the communication channel of the captured data signal when it is determined that the collision signal is transmitted. In the step of transmitting the collision signal,
The communication method according to claim 1, wherein a signal that interrupts propagation of the captured data signal is transmitted as the collision signal. In the step of transmitting the collision signal,
The propagation time of the response signal from the node that received the same data signal as the captured data signal is calculated based on the time when the data signal is captured, and the signal that interrupts the propagation of the response signal is calculated as the collision signal. The communication method according to claim 1, wherein transmission is performed during propagation time. In the step of determining whether to transmit the collision signal,
4. The communication method according to claim 3, wherein it is determined whether or not the size of the captured data signal is appropriate, and it is determined that the collision signal is not transmitted when the determination is negative.   5. The method according to claim 1, further comprising a step of determining a criterion for monitoring a communication status according to the random access method and determining a transmission of the collision signal according to a result of the monitoring. The communication method according to Item 1. In the step of monitoring the communication status by the random access method,
6. The communication method according to claim 5, wherein one or a combination of communication traffic type, flow, data signal size, and bandwidth usage rate is monitored.   The communication method according to claim 1, wherein the communication using the random access method is wireless communication. In the step of determining whether to transmit the collision signal,
Determining whether or not the captured data signal has been retransmitted, and determining that the collision signal is not transmitted if the data signal has been retransmitted and has been transmitted more than a specified number of times. The communication method according to any one of claims 1 to 7, characterized in that: A receiver for capturing a data signal in communication by a random access method;
A control unit that determines whether or not to transmit a collision signal for prompting retransmission of the captured data signal using information included in the data signal;
A control apparatus comprising: a transmission unit that transmits the collision signal to the same communication channel as the communication channel of the captured data signal when it is determined that the collision signal is transmitted.   The control device according to claim 9, wherein the transmission unit transmits, as the collision signal, a signal that interrupts propagation of the data signal captured by the reception unit. The control unit calculates the propagation time of the response signal from the node that received the same data signal as the data signal captured by the receiving unit based on the time when the data signal was captured,
The control device according to claim 9, wherein the transmission unit transmits a signal that interrupts propagation of the response signal as the collision signal during the propagation time calculated by the control unit. 12. The control unit according to claim 11, wherein the control unit determines whether the size of the data signal captured by the reception unit is appropriate, and determines that the collision signal is not transmitted when the determination is negative. Control device.   13. The method according to claim 9, further comprising: a criterion determining unit that monitors a communication status according to the random access method and determines a criterion for determining transmission of the collision signal according to a result of the monitoring. The control device according to any one of claims.   14. The control apparatus according to claim 13, wherein the criterion determining unit monitors one or a combination of a communication traffic type, a flow, a data signal size, and a bandwidth usage rate.   The control apparatus according to claim 9, wherein the communication using the random access method is wireless communication. The control unit determines whether or not the data signal captured by the receiving unit has been retransmitted. If the data signal has been retransmitted and has been retransmitted more than a specified number of times, the collision signal control device according to any one of claims 9 to 15, characterized in that determines not to transmit the.   9. The communication method according to claim 1, wherein the random access method is CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance).   The control device according to claim 9, wherein the random access method is CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance).   A program for causing a computer to function as the control device according to any one of claims 9 to 16 and 18.

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