Communication Management Apparatus, Communication Apparatus, and Communication Method

1. A communication management apparatus that manages transmission of data in a network in which a plurality of communication nodes are connected by an Ethernet, the communication management apparatus comprising: a token-frame receiving unit that receives a token frame for acquiring a transmission right of data and determines whether the transmission right is acquired by analyzing the token frame; a token-frame transmitting unit that transmits the token frame which includes (i) first transmission right acquisition determination information indicating a sequence number of a communication node that can acquire the transmission right in a circulation order of the token frame in the network, (ii) second transmission right acquisition determination information indicating a specific number of frames that can be transmitted while the token frame circulates once, wherein the specific number is variable based on subtracting a number of transmitted data frames from a previously set number of transmittable frames, and (iii) information on another communication node that subsequently acquires the transmission right; and a data-frame-communication processing unit that performs reception processing for data frames from other communication nodes and, when the transmission right is acquired, transmits data in a frame unit, wherein the first transmission right acquisition determination information includes (i) a token circulation number indicating the sequence number counted from the communication management apparatus in the circulation order of the token frame in the network and (ii) a transmission permitted station value indicating the sequence number in the circulation order of the communication node that can transmit a data frame, and the token-frame transmitting unit sets the token circulation number to a value of “1” and sets, in the transmission permitted station value, a value corresponding to information in the received token frame.

2. The communication management apparatus according to claim 1 , wherein the token-frame transmitting unit sets the transmission permitted station value, indicating the sequence number of the own station, to a value of “0” when the second transmission right acquisition determination information of the received token frame is not “0”.

3. The communication management apparatus according to claim 1 , wherein in the received token frame, when the second transmission right acquisition determination information is “0”, and a number of transmittable frames is set to a value of “0” in a setting station information, which indicates a communication apparatus that sets the second transmission right acquisition determination information to a value of “0”, the token-frame receiving unit does not give a transmission instruction for the data frame to the data-frame-communication processing unit, and the token-frame transmitting unit sets the number of transmittable frames to a value of “0” in the setting station information in the transmission permitted station value of the token frame.

4. The communication management apparatus according to claim 3 , further comprising a number-of-transmittable-frames “0” setting-station storing unit that stores contents of the number-of-transmittable-frames “0” setting-station information, wherein the token-frame-receiving unit stores, when the token-frame receiving unit receives the token frame in which the transmission right acquiring apparatus information indicates the own apparatus and the second transmission right acquisition determination information is “0”, contents of the number-of-transmittable-frames “0” setting station information in the number-of-transmittable-frames “0” setting-station storing unit, and the token-frame transmitting unit sets, in the transmission permitted station value, the sequence number of a communication apparatus to which the transmission right is preferentially given when the second transmission right acquisition determination information is “0”.

5. The communication management apparatus according to claim 4 , wherein the token-frame transmitting unit sets, when the second transmission right acquisition determination information of the received token frame is “0”, a start transmission permitted station value and an end transmission permitted station value indicating the sequence number in a range of the communication apparatus to which the transmission right is preferentially given in the transmission permitted station value of the token frame.

6. The communication management apparatus according to claim 4 , wherein, when the number of transmittable frames “0” setting station information is stored in the number-of-transmittable-frames “0” setting-station storing unit, the token-frame transmitting unit sets, when the token-frame transmitting unit receives the token frame in which the transmission right acquiring apparatus information indicates the own apparatus, the number of transmittable frames “0” setting station information in the transmission permitted station value of the token frame and erases the number of transmittable frames “0” setting station information stored in the number-of-transmittable-frames “0” setting-station storing unit.

7. A communication node that receives, in a network in which a plurality of communication nodes are connected by an Ethernet, a token frame for acquiring a transmission right of data circulated according to a circulation order determined by a communication management apparatus and performs transmission of data, the communication node comprising: a token-circulation-destination-information storing unit that stores token circulation destination information indicating the communication node that acquires the transmission right of data next based on the circulation order; a token-frame receiving unit that receives the token frame, determines whether the transmission right is acquired by analyzing the token frame, and determines, when the transmission right is acquired, whether transmission of a data frame is possible using first transmission right acquisition determination information indicating a sequence number of a communication apparatus that can acquire the transmission right in the circulation order and second transmission right acquisition determination information indicating a specific number of transmittable frames at the time of the token frame reception that are stored in the received token frame, wherein the specific number is variable based on subtracting a number of transmitted data frames from a previously set number of transmittable frames; a token-frame transmitting unit that transmits the token frame in which a value obtained by subtracting, when transmission of the data frame is possible, a number of transmitted data frames from the second transmission right acquisition determination information is set in the second transmission right acquisition determination information; and a data-frame-communication processing unit that performs reception processing for data frames from the other communication nodes and, when the transmission right is acquired, transmits data in a frame unit, wherein the first transmission right acquisition determination information includes a token circulation number indicating the sequence number counted from the communication management apparatus in the circulation order and a transmission permitted station value indicating the sequence number in the circulation order of a communication node that can transmit a data frame, and when it is determined that the transmission right is acquired, the token-frame receiving unit determines whether transmission of the data frame is possible using the token circulation number and the transmission permitted station value.

8. The communication node according to claim 7 , wherein the token-frame transmitting unit sets, as a new version of the token circulation number, the token circulation number of the received token frame incremented by one.

9. The communication node according to claim 7 , wherein when the token circulation number in the token frame is equal to or larger than the transmission permitted station value and the second transmission right acquisition determination information is larger than “0”, the token-frame receiving unit determines that transmission of a data frame is possible, and the data-frame-communication processing unit transmits the data frame within a range of the second transmission right acquisition determination information.

10. The communication node according to claim 9 , wherein the token frame stores number of transmittable frames “0” setting station information indicating a communication node that sets the second transmission right acquisition determination information to “0”, and when a value obtained by subtracting a number of transmitted data frames from second transmission right acquisition determination information in a received token frame changes to “0”, the token-frame transmitting unit sets a value of the token circulation number in the received token frame in the number of transmittable frames “0” setting station information.

11. A communication method for data employing a token frame in a communication system that manages transmission of data in a network in which a plurality of communication nodes are connected by an Ethernet cable and includes a communication management apparatus that is one of the communication nodes and communication apparatuses that are the other communication nodes in the network, the communication method comprising: a transmission right determining step for determining, by the communication management apparatus, whether a communication node in the plurality of communication nodes indicated by transmission right acquiring apparatus information that acquires a transmission right next in the received token frame is the own apparatus; a first data frame transmitting step for transmitting, by the communication management apparatus, when the transmission right acquiring apparatus information indicates the own apparatus, data in a transmission waiting state in a frame unit; a first token frame transmitting step for transmitting, by the communication management apparatus, the token frame which includes (i) first transmission right acquisition determination information indicating a sequence number of a communication apparatus that can acquire the transmission right in token circulation order for circulating the token frame in the network, (ii) second transmission right acquisition determination information indicating a specific number of frames that can be transmitted while the token frame circulates once from the own station, wherein the specific number is variable based on subtracting a number of transmitted data frames from a previously set number of transmittable frames, and (iii) transmission right acquiring apparatus information that is a next transmission destination of the token frame after the own apparatus acquired from the token circulation order; a token-frame-acquisition determining step for determining, by the communication apparatus, whether the transmission right acquiring apparatus information of the received token frame indicates the own apparatus; a first transmission right determining step for determining, by the communication apparatus, when the transmission right acquiring apparatus information indicates the own apparatus, using the first transmission right acquisition determination information, whether the own station has the transmission right; a second transmission right determining step for determining, by the communication apparatus, when it is determined in the first transmission right determining step that the own station has the transmission right, possibility of transmission of data frames using the second transmission right acquisition determination information; a second data frame transmitting step for transmitting, by the communication apparatus, when it is determined that the data frames can be transmitted in the second transmission right determining step, the data frames within a range of the second transmission right acquisition determination information; and a second token frame transmitting step for setting, by the communication apparatus, after it is determined in the first transmission right determining step that the own station does not have the transmission right, after it is determined in the second transmission right determining step that the data frames cannot be transmitted, or after the data frames are transmitted in the data frame transmitting step, in the transmission right acquiring apparatus information, token circulation destination information indicating the communication node in the plurality of communication nodes to which the transmission right is given after the own station, and transmitting, when the data frames are transmitted in the second data frame transmitting step, the token frame in which a value obtained by subtracting a number of the data frames from the second transmission right acquisition determination information at the time of the token frame reception has been set in the second transmission right acquisition determination information, wherein the first transmission right acquisition determination information includes a token circulation number indicating the sequence number based on the communication management apparatus in the token circulation order of a communication apparatus set in the transmission right acquiring apparatus information and a transmission permitted station value indicating a sequence number in the token circulation order of a communication apparatus that can transmit a data frame in the data frames, in the first token frame transmitting step, the communication management apparatus sets “1” in the token circulation number and sets, in the transmission permitted station value, a value corresponding to information set in the received token frame, in the first transmission right determining step, the communication apparatus determines presence or absence of the transmission right using the token circulation number and the transmission permitted station value, and in the second token frame transmitting step, the communication apparatus sets, in the token circulation number, the sequence number indicating the token circulation destination information.

12. The communication method according to claim 11 , wherein, in the second token frame transmitting step, the communication apparatus sets, as a new version of the token circulation number, the token circulation number of the received token frame incremented by one.

13. The communication method according to claim 11 , wherein in the first transmission right determining step, when the token circulation number in the token frame is equal to or larger than the transmission permitted station value, the communication apparatus determines that the own station has the transmission right, in the second data frame transmitting step, when the second transmission right acquisition determination information is larger than “0”, the communication apparatus determines that frames can be transmitted, in the second data frame transmitting step, the communication apparatus attaches, to data that is in a transmission waiting state at the time of the token frame reception and could not be transmitted, last-time un-transmitted data identification information for identifying the data that could not be transmitted within a range of the second transmission right acquisition determination information, in the second token frame transmitting step, when the second transmission right acquisition determination information is “0” in the transmission of the data frame, the communication apparatus sets a value of the token circulation number at the time of the token frame reception in number of transmittable frames “0” setting station information indicating the communication node in the plurality of communication nodes that has set the second transmission right acquisition determination information to “0”, in the transmission right determining step, when the transmission right acquiring apparatus information in the received token frame indicates the own apparatus, the second transmission right acquisition determination information is “0”, and the number of transmittable frames “0” setting station information has been set, the communication management apparatus determines that the transmission right has not been obtained, and in the first token frame transmitting step, the communication management apparatus further sets the number of transmittable frames “0” setting station information in the transmission permitted station value of the token frame.

14. The communication method according to claim 13 , wherein, in the second data frame transmitting step, when the communication apparatus has data attached with the last-time un-transmitted data identification information, the communication apparatus transmits only the data attached with the last-time un-transmitted data identification information at the time of transmission right acquisition.

15. The communication method according to claim 11 , wherein, in the second data frame transmitting step, when the token circulation number is equal to or larger than the transmission permitting station value and the second transmission right acquisition determination information is “0”, the communication apparatus attaches, to data that is in a transmission waiting state at the time of the token frame reception and could not be transmitted, last-time un-transmitted data identification information for identifying the data that could not be transmitted.

16. The communication method according to claim 15 , wherein, in the second data frame transmitting step, when the communication apparatus has data attached with the last-time un-transmitted data identification information, the communication apparatus transmits only the data attached with the last-time un-transmitted data identification information at the time of transmission right acquisition.

17. The communication method according to claim 11 , wherein, in the first token frame transmitting step, the communication management apparatus sets, as the second transmission right acquisition determination information, a number of frames that can be received at a point when the token frame in which the transmission right acquiring apparatus information indicates the own apparatus is received.

18. The communication method according to claim 11 , wherein in the transmission right determining step, when the communication management apparatus receives the token frame in which the second transmission right acquisition determination information is “0”, the communication management apparatus stores contents of the number of transmittable frames “0” setting station information, and in the token frame transmitting step, when the second transmission right acquiring apparatus information is “0”, the communication management apparatus sets, in the transmission permitted station value, changed destination information during priority processing that is the sequence number of the communication apparatus to which the transmission right is preferentially given.

19. The communication method according to claim 18 , wherein when the second transmission right acquisition determination information is “0”, the changed destination information during priority processing includes a start transmission permitted station value and an end transmission permitted station value indicating the sequence number in a range of the communication apparatus to which the transmission right is preferentially given, and in the first transmitting right determining step, when the token circulation number is present within a range indicated by the start transmission permitted station value and the end transmission permitted station value, the communication apparatus determines that the own station has the transmission right.

20. The communication method according to claim 18 , wherein, in the first token frame transmitting step, when contents of the number of transmittable frames “0” setting station information are stored at the time of reception of the token frame in which the transmission right acquiring apparatus information indicates the own apparatus, the communication management apparatus sets the stored number of transmittable frames “0” setting stating information in the transmission permitted station value.