Patent Publication Number: US-8976811-B2

Title: Communication apparatus, communication system and communication method

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2011-237766, filed on Oct. 28, 2011, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiment discussed herein is related to a communication apparatus, a communication system and a communication method in a network. 
     BACKGROUND 
     An M2M (Machine-to-Machine) system is automatically controlled in such a way that machines, or a machine and an information system, coupled to a network exchange information with each other without a human operation. 
     The M2M system includes a plurality of machines each equipped with a communication apparatus to be an M2M terminal, and the plural machines exchange information with the information system. 
     Japanese National Publication of International Patent Application No. 2006-526372 discusses a related art. 
     SUMMARY 
     According to one aspect of the embodiments, a communication apparatus includes: a storage section configured to store a communication throughput of each of a plurality of communication apparatuses, a reference value of the communication throughput and a reference adjustment value to adjust the reference value; a calculating section configured, when a current communication throughput between a self-sided communication apparatus and a center apparatus exceeds a self reference value, to calculate a reference value of each of the plurality of communication apparatuses based on an upper limit value, the current communication throughput, and the communication throughput and the reference adjustment value in the storage section, the upper limit value corresponding to a total communication throughput of the plurality of communication apparatuses; an updating section configured to update the reference value in the storage section with the calculated reference value in the plurality of communication apparatuses; a transmitter section configured to transmit the calculated reference value to an external communication apparatus; and a receiver section configured to receive the calculated reference value transmitted from the external communication apparatus and update the reference value in the storage section with the calculated reference value. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  depicts an exemplary M2M system; 
         FIG. 2  depicts an exemplary communication apparatus; 
         FIG. 3  depicts an exemplary process to of a M2M system; 
         FIG. 4  depicts an exemplary transmitted/received record storage section; 
         FIG. 5  depicts an exemplary limit value table; 
         FIG. 6  depicts an exemplary process of a self-sided node limit value watcher; 
         FIG. 7  depicts an exemplary process of a self-sided node limit value watcher; 
         FIG. 8  depicts an exemplary limit value and an exemplary transmitted data amount; 
         FIG. 9  depicts an exemplary limit value and an exemplary transmitted data amount; 
         FIG. 10  depicts an exemplary limit value and an exemplary transmitted data amount; 
         FIG. 11  depicts an exemplary change in a margin rate; 
         FIG. 12  depicts an exemplary process of a limit value calculator; 
         FIG. 13  depicts an exemplary process of a data transceiver; 
         FIG. 14  depicts an exemplary data transmission decision table; and 
         FIG. 15  depicts an exemplary identifier. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     An upper limit to a total communication throughput of all M2M terminals in an M2M system is set for a certain period of time to use a network. The M2M system may employ a rate schedule in which charges for network use for communication are significantly raised if a total communication throughput exceeds the upper limit. 
     Thus, the M2M terminals may notify each other of their communication throughput and adjust the communication throughput with each other in order that the total communication throughput remains lower than the upper limit. 
     A terminal station generates a packet including transmission information based on size of data in a buffer portion and the data, and transmits the packet to an external terminal station. A control station receives the packet transmitted by the terminal station, and decides whether a currently allotted frequency band is to be changed or not based on the transmission information obtained from the received packet. Upon changing the frequency band, the control station transmits a packet to notify the terminal station and the external terminal station of a new frequency band. 
     If, e.g., the number of terminal stations increases, a load of the control station may increase. The control station changes allotments of frequency bands and does not reduce communication throughput. Thus, the control station may fail to control the total throughput in the M2M system so as to keep it lower than the upper limit. 
       FIG. 1  depicts an exemplary M2M system. To-be managed devices  10 A and  10 B illustrated in  FIG. 1  are coupled to communication apparatuses  20 A and  20 B as M2M terminals, respectively, via a Local Area Network (LAN) cable or a serial communication line. The communication apparatuses each may be referred as a node. 
     The to-be-managed devices  10 A and  10 B may be, e.g., a machine tool for manufacturing mechanical parts. The managed  10 A and  10 B devices packetize a log of kinds and quantities of manufactured mechanical parts or information such as operation conditions, alarms, etc. The to-be-managed devices  10 A and  10 B provide the communication apparatuses  20 A and  20 B, respectively, with a packet to notify a center apparatus  40  of the information. 
     The communication apparatuses  20 A and  20 B each include a data transceiver  21 , a self-sided node limit value watcher  22 , a limit value calculator  23 , an external node data transceiver  24 , a self-sided node limit value updater  25 , a transmitted/received record storage section  26 , a limit value table  27  and a data transmission decision table  28 . 
     The data transceiver  21  is coupled to the to-be-managed devices ( 10 A,  10 B, etc.) and transmits and receives data to and from the to-be-managed devices. The data transceiver  21  is coupled to an IP (Internet Protocol) network  30 . The data transceiver  21  decides whether packetized transmission data received from the to-be-managed device is allowed to be transmitted. The data transceiver  21  transmits the packetized transmission data to the center apparatus  40  via the IP network  30 . The data transceiver  21  decides whether the packetized transmission data is allowed to be transmitted based on an identifier included in the transmission data. The data transceiver  21  replies to a packet transmitted from the center apparatus  40 . 
     The data transceiver  21  obtains an identifier which indicates transmission from the data transmission decision table  28 . If an identifier which indicates transmission is present in transmission data received from the to-be-managed device, the data transceiver  21  transmits the transmission data to the center apparatus  40 . 
     The self-sided node limit value watcher  22  compares a total throughput of data transmitted by the self-sided node stored in the transmitted/received record storage section  26  with a limit value of the self-sided node stored in the limit value table  27 . The limit value may be a reference value of communication throughput. If the total throughput of data transmitted by the self-sided node exceeds the limit value of the self-sided node, the self-sided node limit value watcher  22  requests one or a plurality of external nodes stored in the limit value table  27  to notify the self-sided node of a limit value and a throughput of transmitted data. 
     The self-sided node limit value watcher  22  provides the limit value calculator  23  with the limit value and the throughput of transmitted data, which have been notified by one or more of the external nodes, and the limit value and the (total) throughput of transmitted data of the self-sided node, so as to make the limit value calculator  23  calculate limit values of the self-sided node and the external nodes. The self-sided node limit value watcher  22  provides the self-sided node limit value updater  25  with the limit values of the self-sided node and the external nodes calculated by the limit value calculator  23 , so as to make the self-sided node limit value updater  25  update the limit value table  27 . 
     The limit value calculator  23  calculates the limit values of the self-sided node and the external nodes based on the limit value and the throughput of transmitted data received from one or more of the external nodes provided by the self-sided node limit value watcher  22 , and the limit value and the throughput of transmitted data of the self-sided node, and returns the calculation result to the self-sided node limit value watcher  22 . 
     The external node data transceiver  24  transmits and receives data such as a limit value and a throughput of transmitted data to and from a communication apparatus of an external node, e.g., by using a Wireless LAN (WLAN). The external node data transceiver  24  provides the self-sided node limit value watcher  22  with limit values of the self-sided node and the external nodes received from an external node. 
     A list of a communication apparatus to be an external node when the external node data transceiver  24  transmits and receives data may be set in advance, or may be dynamically updated by the use of technologies of ad hoc communication. The communication apparatuses each have functions of a router, an L3 switch, etc., and independently perform routing operations in the ad hoc communication. Therefore, a coverage of data exchange of the external node data transceiver  24  may expand so as to communicate with a communication apparatus located far from the self-sided node. 
     The self-sided node limit value updater  25  stores the limit values of the self-sided node and the external nodes calculated by the limit value calculator  23  and provided by the self-sided node limit value watcher  22  in the limit value table  27 , so as to update the limit value table  27 . 
     History data of data exchange with the center apparatus  40  is stored in the transmitted/received record storage section  26 . The limit values of the self-sided node and the external nodes are stored in the limit value table  27 . 
     An identifier and a margin rate are set in the data transmission decision table  28  according to an alarm and a log type of a packet from the device to be managed. The margin rate may be a criterion in deciding whether the packet from the to-be-managed device is to be transmitted to the center apparatus  40 . 
     The communication apparatuses  20 A and  20 B depicted in  FIG. 1  may be configured to transmit a packet received from the to-be-managed device  10 A and from the to-be-managed device  10 B, respectively, to the center apparatus  40  by means of the data transceiver  21  independently from each other. The communication apparatus  20 B provided next to the to-be-managed  10 A may transmit a packet received from the to-be-managed device  10 B to the communication apparatus  20 A by using the external node data transceiver  24 . The communication apparatus  20 A may be configured to transmit a packet received from the adjacent to-be-managed device  10 B, etc., with a packet received from the to-be-managed device  10 A by the self-sided node collectively to the center apparatus  40  by means of the data transceiver  21 . 
       FIG. 2  depicts an exemplary communication apparatus.  FIG. 2  may depict a hardware constitution of the communication apparatus  20 A or  20 B. The communication apparatus  20 A depicted in  FIG. 2  includes a CPU  51 , a memory (MEM)  52 , a LAN communication apparatus  53 , a WLAN communication apparatus  54  and a wireless communication apparatus  55 . The apparatuses from the CPU  51  to the wireless communication apparatus  55  are coupled with one another. 
     The CPU  51  runs data processing programs stored in the memory  52  to transmit and receive data, to watch a self-sided node limit value, to calculate a limit value, to transmit and receive data to and from an external node, or to update a self-sided node limit value. The data processing programs are executed so that the data transceiver  21 , the self-sided node limit value watcher  22 , the limit value calculator  23 , the external node data transceiver  24  and the self-sided node limit value updater  25  depicted in  FIG. 1  work. 
     The memory  52  includes a ROM in which a data processing program is stored, a RAM to be used as a working area, and a non-volatile memory such as a flash memory in which data is stored. The transmitted/received record storage section  26  works on the non-volatile memory in the memory  52 , and so does the limit value table  27  and the data transmission decision table  28 . 
     The LAN communication apparatus  53  is coupled, e.g., to a LAN communication apparatus in the device to be managed  10 A, and transmits and received data to and from the to-be-managed device. The LAN communication apparatus  53  may correspond to a portion of the data transceiver  21  depicted in  FIG. 1 . 
     The WLAN communication apparatus  54  is coupled by wireless to an external apparatus, for example, a WLAN communication apparatus as an external node, and performs wireless communication including ad hoc communication. The WLAN communication apparatus  54  may correspond to the external node data transceiver  24  depicted in  FIG. 1 . 
     The wireless communication apparatus  55  is coupled to a wireless base station in a mobile communication system and performs wireless communication, so as to be coupled to the center apparatus  40  via the IP network  30  and to perform data communication. The wireless communication apparatus  55  may correspond to a portion of the data transceiver  21 . 
       FIG. 3  illustrates an exemplary data process operation of a M2M system. The to-be-managed device  10 A depicted in  FIG. 3  transmits a packet including information of a log, an alarm, etc. to the center apparatus  40  via the communication apparatus  20 A (sequence SQ 1 ). The center apparatus  40  transmits a reply to the to-be-managed device  10 A via the communication apparatus  20 A so as to transmit and receive data (sequence SQ 2 ). 
     Upon finishing transmitting and receiving data, the data transceiver  21  in the communication apparatus  20 A stores throughput values of transmitted data and received data in the transmitted/received record storage section  26  (sequence SQ 3 ). 
       FIG. 4  depicts an exemplary transmitted/received record storage section. As depicted in  FIG. 4 , the throughput of transmitted data and received data are stored in associated with a destination IP address, time when transmission starts and time when transmission ends. The throughput of transmitted data and received data may be expressed, e.g., in the number of bytes or in the number of packets. What is stored in the transmitted/received record storage section  26  is reset by the self-sided node limit value watcher  22  each time a charge period ends, e.g., every month. The throughput of transmitted data and received data may thereby be easily managed. 
     The self-sided node limit value watcher  22  compares a sum of throughput of data transmitted by the self-sided node, i.e., a communication throughput stored in the transmitted/received record storage section  26  with a self-sided node limit value stored in the limit value table  27  (sequence SQ 4 ). 
     If the sum of the throughput of data transmitted by the self-sided node, e.g., the communication throughput, exceeds the self-sided node limit value, the self-sided node limit value watcher  22  requests an external node which is listed in the limit value table  27 , e.g., the communication apparatus  20 B, to notify the self-sided node from the external node data transceiver  24  of a limit value, a (total) throughput of transmitted data and a margin rate (sequence SQ 5 ). The sum of the throughput of data transmitted by the self-sided node is the communication throughput to be compared with the limit value. The throughput of received data may be added to the throughput of transmitted data, and the sum of the throughput of data transmitted and received by the self-sided node may be the communication throughput to be compared with the limit value. 
       FIG. 5  depicts an exemplary limit value table. As depicted in  FIG. 5 , a node name of a packet self-sided node and a node name of an external node which transmits and receives data to and from the self-sided node by using the external node data transceiver  24 , e.g., a name of the communication apparatus (or maybe an address of the external node) are stored. Time when data is updated, the (total) throughput of transmitted data, the limit value and the margin rate are stored for every node name. The margin rate may be a value for adjusting the limit value, and may be referred as a reference adjustment value. 
     The nodes depicted in  FIG. 5  each keeps a distinctive margin rate, receive the limit value, the (total) throughput of transmitted data and the margin rate, and calculate the limit value for every node. An upper limit may be stored in the limit value table  27 , although not depicted in  FIG. 5 . The upper limit may be set to a total throughput of data transmitted by all the communication apparatuses in the M2M system for a certain period of time. If the total throughput of communication for a certain period of time exceeds the upper limit, charges for use of communication may be raised. 
     Upon receiving a request from the communication apparatus  20 A for notification of the limit value and the throughput of transmitted data, the communication apparatus  20 B as an external node reads the self-sided node limit value and the (total) throughput of transmitted data from the limit value table  27 , and transmits what is read via the external node data transceiver  24  back to the communication apparatus  20 A (sequence SQ 6 ). 
     If the communication apparatuses  20 A and  20 B are installed so apart from each other that the external node data transceiver  24  is unable to transmit or receive data, the data transmission and reception may be performed via the IP network  30  by the use of the data transceiver  21 . 
     The sequence SQ 5  and the sequence SQ 6  may be omitted. As latest (total) throughput of transmitted data is obtained from every node if the sequences SQ 5  and SQ 6  are executed, the limit values of the self-sided node and the external node may be exactly calculated in a next sequence SQ 7 . 
     The self-sided node limit value watcher  22  in the communication apparatus  20 A makes the limit value calculator  23  calculate the limit values of the self-sided node and the external node based on the (total) throughput of transmitted data and the margin rate from the communication apparatus  20 B, and of the (total) throughput of transmitted data and the margin rate of the self-sided node. The self-sided node limit value watcher  22  makes the self-sided node limit value updater  25  update the limit value table  27  on the calculated limit values of the self-sided and external nodes (sequence SQ 7 ). 
     The self-sided node limit value watcher  22  instructs the communication apparatus  20 B as the external node via the self-sided node limit value updater  25  to update the limit value table  27  with the calculated limit values of the self-sided and external nodes (sequence SQ 8 ). 
     The communication apparatus  20 B receives the instructions from the communication apparatus  20 A by means of the external node data transceiver  24 , and provides the self-sided node limit value watcher  22  with the instructions. The self-sided node limit value watcher  22  in the communication apparatus  20 B provides the self-sided node limit value updater  25  with the limit values of the self-sided node and the external nodes received from the communication apparatus  20 A, and makes the self-sided node limit value updater  25  update the limit value table  27  (sequence SQ 9 ). 
       FIG. 6  depicts an exemplary process of a self-sided node limit value watcher. The process depicted in  FIG. 6  may be a process performed by the self-sided node limit value watcher  22  in the communication apparatus  20 A as the self-sided node illustrated in  FIG. 3 . The self-sided node limit value watcher  22  obtains, in an operation S 1 , the total throughput of data transmitted by the self-sided node to be stored in the transmitted/received record storage section  26  and the limit value of the self-sided node stored in the limit value table  27 . 
     The self-sided node limit value watcher  22  decides whether the total throughput of transmitted data exceeds the limit value of the self-sided node in an operation S 2 . Unless the total throughput of transmitted data exceeds the limit value of the self-sided node, the process goes to the operation S 1 . If the total throughput of transmitted data exceeds the limit value of the self-sided node, the self-sided node limit value watcher  22  obtains the limit value, the (total) throughput of transmitted data and the margin rate of the external node by using the external node data transceiver  24  in an operation S 3 . 
     The self-sided node limit value watcher  22  makes the limit value calculator  23  calculate limit values of the self-sided node and the external nodes based on the limit value and the throughput of transmitted data received from the external node and the throughput of transmitted data and the margin rate of the self-sided node (tonal) in an operation S 4 . The self-sided node limit value watcher  22  makes the self-sided node limit value updater  25  update the limit value table  27  with the calculated limit values of the self-sided and external nodes as an operation S 5 . 
     The self-sided node limit value watcher  22  transmits instructions to update the calculated limit values of the self-sided node and the external nodes, the (total) throughput of transmitted data and the margin rate to every external node via the external node data transceiver  24 , and makes each of the external nodes update the limit value table  27  in an operation S 6 . The process goes to the operation S 1  and the operations S 1  through S 6  are repeated. 
       FIG. 7  depicts an exemplary process of a self-sided node limit value watcher. The process depicted in  FIG. 7  may be a process which is performed by the self-sided node limit value watcher  22  in the communication apparatus  20 B as the external node illustrated in  FIG. 3 . The process depicted in  FIG. 7  may be started upon receiving a request from the external node for notification of the limit value and the throughput of transmitted data. 
     The external node data transceiver  24  receives a request from the external node for notification of the limit value and the throughput of transmitted data in an operation S 11 . 
     The self-sided node limit value watcher  22  reads the limit value, the (total) throughput of transmitted data and the margin rate of the self-sided node from the limit value table  27  in an operation S 12 . The self-sided node limit value watcher  22  transmits the data read from the external node data transceiver  24  to the communication apparatus  20 A in an operation S 13 . 
     The self-sided node limit value watcher  22  receives instructions to update the limit values of the self-sided node and the external nodes in an operation S 14 . The self-sided node limit value watcher  22  updates the limit value table  27  with the received limit values of the self-sided and external nodes, a (total) throughput of data and the margin rate in an operation S 15 . 
     The self-sided node limit value watcher  22  replies that the table is fully updated in an operation S 16 . The process goes to the operation S 11  and the operations S 11  through S 16  are repeated. The operation S 16  may be omitted. 
     If equal values are set to margin rates of all transmitters, the communication apparatuses may omit to transmit and receive the margin rates to and from one another. 
       FIGS. 8-10  illustrate an exemplary limit value and an exemplary throughput of transmitted data.  FIGS. 8-10  may indicate state transitions of limit values and (total) throughput values of data transmitted by a plurality of communication apparatuses  10 A- 10 E. An upper limit of (total) throughput of data transmitted by the communication apparatuses  10 A- 10 E for a certain period of time, e.g., one month may be set to 500. If the throughput exceeds the upper limit, charges for network use may be raised. Margin rates of the respective communication apparatuses each may be 0.5. 
       FIG. 8  depicts an initial state (state  1 ) in which none of the communication apparatuses  10 A- 10 E performs data communication. The limit value R of each of the communication apparatuses is calculated according to a following equation (1) by the use of a margin X of the throughput of transmitted data for the upper limit, the number Y of the communication apparatuses and the margin rate Z. 
     
       
         
           
             
               
                 
                   
                     
                       
                         R 
                         = 
                           
                         ⁢ 
                         
                           
                             ( 
                             
                               X 
                               / 
                               Y 
                             
                             ) 
                           
                           × 
                           Z 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             [ 
                             
                               
                                 ( 
                                 
                                   500 
                                   - 
                                   0 
                                 
                                 ) 
                               
                               / 
                               5 
                             
                             ] 
                           
                           × 
                           0.5 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         50 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Data communication of a throughput value  60  of transmitted data may occur on the communication apparatus  10 A in the state  1 . The limit value calculator  23  in the communication apparatus  10 A calculates limit values of the self-sided and external nodes by using the equation (1). The communication apparatuses  10 A- 10 E may shift to a state  2  depicted in  FIG. 9 . 
     
       
         
           
             
               
                 
                   R 
                   = 
                     
                   ⁢ 
                   
                     
                       [ 
                       
                         
                           ( 
                           
                             500 
                             - 
                             60 
                           
                           ) 
                         
                         / 
                         5 
                       
                       ] 
                     
                     × 
                     0.5 
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   44 
                 
               
             
           
         
       
     
     Data communication of a throughput value  70  of transmitted data may occur on the communication apparatus  10 C in the state  2 . The limit value calculator  23  in the communication apparatus  10 C calculates limit values of the self-sided node and the external nodes by using the equation (1). The communication apparatuses  10 A- 10 E shift to a state  3  depicted in  FIG. 10 . 
     
       
         
           
             
               
                 
                   R 
                   = 
                     
                   ⁢ 
                   
                     
                       [ 
                       
                         
                           ( 
                           
                             500 
                             - 
                             130 
                           
                           ) 
                         
                         / 
                         5 
                       
                       ] 
                     
                     × 
                     0.5 
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   37 
                 
               
             
           
         
       
     
     The margin rates of the communication apparatuses depicted in  FIGS. 8-10  each may be fixed to 0.5, or may be variably set based on the total throughput of data transmitted by the communication apparatuses  10 A- 10 E.  FIG. 11  depicts an exemplary change in a margin rate.  FIG. 11  depicts a change in the margin rate with respect to the total throughput of transmitted data. As depicted in  FIG. 11 , the total throughput of transmitted data being 0 through 250 corresponds to a level 1 and the margin rate is set to 0.5. The total throughput of transmitted data being 250 through 400 corresponds to a level 2 and the margin rate is set to 0.8. The total throughput of transmitted data being 400 through 500 or greater than 500 corresponds to a level 3 and the margin rate is set to 1.0. 
     As the total throughput of transmitted data increases, the margin rate of each of the communication apparatuses increases and the limit value becomes closer to the upper limit. 
     A number of the margin rates may be four or more levels. The margin rate may be preset for every level by the limit value calculator  23  of each of the communication apparatuses. The center apparatus  40  may change the setting of the margin rate for every level and every communication apparatus. The number of margin rates or the margin rates for each of the levels may be different for each of the communication apparatuses. 
       FIG. 12  depicts an exemplary process of a limit value calculator. The process depicted in  FIG. 12  may be a process which is performed by the limit value calculator  23  in the operation S 4  depicted in  FIG. 6  when the margin rate for the total throughput of transmitted data changes. Before the process depicted in  FIG. 12  starts, an integer N may be set to one. 
     The limit value calculator  23  adds up the throughput f data transmitted by all of the nodes in an operation S 21  as depicted in  FIG. 12 . The limit value calculator  23  decides whether the total throughput of transmitted data exceeds the upper limit multiplied by the margin rate of a level N in an operation S 22 . If the total throughput of transmitted data exceeds the upper limit multiplied by the margin rate of the level N, the limit value calculator  23  incrementally updates the integer N by one in an operation S 23 . The limit value calculator  23  obtains the margin rate of the level N after being incrementally updated, and updates the margin rate of the self-sided node in the limit value table  27 . The process goes to the operation S 22 . 
     Unless the total throughput of transmitted data exceeds the upper limit multiplied by the margin rate of the level N in the operation S 22 , the process goes to an operation S 24 . The limit value calculator  23  calculates the limit values of the self-sided and external nodes according to the equation (1). 
       FIG. 13  depicts an exemplary process of a data transceiver. The process depicted in  FIG. 13  may be a transmission decision process which is performed by the data transceiver  21 . The process depicted in  FIG. 13  may be performed in response to receiving a packet including data such as a log or an alarm from the to-be-managed device, for example, receiving data to be transmitted to the center apparatus  40 . 
     The data transceiver  21  receives data to be transmitted to the center apparatus  40  in an operation S 31 . The data transceiver  21  obtains an identifier indicating transmission from the data transmission decision table  28  based on the current margin rate (or its level) of the self-sided node in an operation S 32 . 
       FIG. 14  depicts an exemplary data transmission decision table. As depicted in  FIG. 14 , an identifier and a margin rate (level 1, 2 or 3) are set to each of entries corresponding to packet types of transmitted data, i.e., “Alarm (Alert)”, “Alarm (Warning)”, “Alarm (Info)”, “Log level 1”, “Log level 2”, “Log level 3” and “Log level 4”. 
       FIG. 15  depicts an exemplary identifier. An alarm/log type having a margin rate being higher than the current margin rate may be obtained as an identifier indicating transmission in an operation S 32 . If the current margin rate is 0.5 (level 1), the entries “Alarm (Alert)”, “Alarm (Warning)”, “Alarm (Info)”, “Log level 1”, “Log level 2”, “Log level 3” and “Log level 4” each may be obtained as an identifier indicating transmission. If the current margin rate is 0.8 (level 2), the entries “Alarm (Alert)”, “Alarm (Warning)”, “Log level 1” and “Log level 2” each may be obtained as an identifier indicating transmission. If the current margin rate is 0.1 (level 3), the entries “Alarm (Alert)” and “Log level 1” each may be obtained as an identifier indicating transmission. Those conditions are depicted in  FIG. 15 . 
     After performing the operation S 32 , the data transceiver  21  decides in an operation S 33  whether received transmission data includes an identifier indicating transmission obtained from the data transmission decision table  28 . If the transmission data includes an identifier indicating transmission, the data transceiver  21  transmits the transmission data to the center apparatus  40  in an operation S 34 . If the transmission data includes no identifier indicating transmission, the data transceiver  21  discards the transmission data without transmitting the transmission data in an operation S 35 . 
     The communication apparatus does not transmit the throughput of transmitted data and the limit value to the external communication apparatus each time transmitting data. The communication apparatus transmits the throughput of transmitted data, the limit value and the margin rate to the external communication apparatus if the throughput of transmitted data exceeds the limit value. Thus, as the plurality of communication apparatuses each autonomously control a reference value of communication throughput, the communication apparatuses may communicate with one another less frequently, and the communication throughput may be reduced. 
     As the total throughput of data transmitted by all the communication apparatuses approaches to the upper limit, the current margin rate of the communication apparatus increases (or the level of the margin rate increases). As the margin rate increases (or the level of the margin rate increases), the data transceiver  21  discards larger size of transmission data. Thus, the total throughput of transmitted data may exceed the upper limit less frequently, and charges for network use for communication may be reduced. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment of the present invention has been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.