We Claim:
1. A communication apparatus mounted on a train, the
communication apparatus forming a train communication
system together with a system control apparatus that
generates control frames, the communication apparatus
comprising:
a general transfer processing unit to store a general frame among the control frames;
a low latency transfer processing unit to store a low latency frame among the control frames, the low latency frame being required to be transferred with lower latency than the general frame;
a frame identification unit to identify priority of each of the control frames received from the system control apparatus and perform control that outputs the control frame to the general transfer processing unit or the low latency transfer processing unit on the basis of a priority setting table that indicates the priority of the control frame, the priority setting table being set in the frame identification unit;
an output control unit to preferentially transfer the low latency frame stored in the low latency transfer processing unit over the general frame stored in the general transfer processing unit; and
a control unit to perform control that modifies the priority setting table of the frame identification unit.
2. The communication apparatus according to claim 1,
wherein
the control unit monitors traffic of the low latency frame in the low latency transfer processing unit and, when the traffic is higher than or equal to a predetermined threshold, transmits a first notification frame to the

system control apparatus and receives a first priority setting frame from the system control apparatus, the first notification frame indicating that the traffic is higher than or equal to the threshold, the first priority setting frame being a response to the first notification frame, the control unit modifying the priority setting table on the basis of the first priority setting frame such that a control frame having low priority among the control frames treated as the low latency frames is treated as the general frame.
3. The communication apparatus according to claim 2,
wherein
the control unit monitors the traffic even after modifying the priority setting table and, when the traffic is less than the threshold, transmits a second notification frame to the system control apparatus and receives a second priority setting frame from the system control apparatus, the second notification frame indicating that the traffic is less than the threshold, the second priority setting frame being a response to the second notification frame, the control unit modifying the priority setting table on the basis of the second priority setting frame such that a control frame having high priority among the control frames treated as the general frames is treated as the low latency frame again.
4. The communication apparatus according to claim 2 or 3,
wherein
the control unit starts monitoring the traffic on the basis of an instruction from the system control apparatus to start monitoring the traffic.

5. The communication apparatus according to claim 4,
wherein
the control unit finishes monitoring the traffic on the basis of an instruction from the system control apparatus to finish monitoring the traffic.
6. The communication apparatus according to claim 1,
wherein
the control unit monitors traffic of the low latency frame in the low latency transfer processing unit and, when the traffic is higher than or equal to a predetermined threshold, modifies the priority setting table such that a control frame having low priority among the control frames treated as the low latency frames is treated as the general frame.
7. The communication apparatus according to claim 6,
wherein
the control unit monitors the traffic even after modifying the priority setting table and, when the traffic is less than the threshold, modifies the priority setting table such that a control frame having high priority among the control frames treated as the general frames is treated as the low latency frame again.
8. The communication apparatus according to claim 6 or 7,
wherein
the control unit starts monitoring the traffic after the train is started, cars of the train split, or the cars of the train are combined together.
9. The communication apparatus according to claim 8,
wherein

the control unit finishes monitoring the traffic after a predetermined time elapses from the start of the monitoring of the traffic.
10. A system control apparatus mounted on a train, the
system control apparatus forming a train communication
system together with a communication apparatus that
transfers control frames, the communication apparatus
having a priority setting table set therein, the priority
setting table indicating priority of the control frames,
the system control apparatus comprising:
a frame reception unit to receive, from the communication apparatus according to any one of claims 2 to 5, a first notification frame indicating that traffic of a low latency frame in the communication apparatus is higher than or equal to a predetermined threshold;
a command unit to instruct generation of a first priority setting frame that is a response to the first notification frame and instructs a modification to the priority setting table such that a control frame having low priority among the control frames treated as the low latency frames is treated as a general frame;
a priority setting frame generation unit to generate the first priority setting frame; and
an output control unit to transmit the first priority setting frame to the communication apparatus.
11. The system control apparatus according to claim 10,
wherein
the frame reception unit receives, from the communication apparatus, a second notification frame indicating that the traffic is less than the threshold,
the command unit instructs the priority setting frame

generation unit to generate a second priority setting frame that is a response to the second notification frame and instructs a modification to the priority setting table such that a control frame having high priority among the control frames treated as the general frames is treated as the low latency frame again,
the priority setting frame generation unit generates the second priority setting frame, and
the output control unit transmits the second priority setting frame to the communication apparatus.
12. The system control apparatus according to claim 10 or
11, wherein
the command unit instructs the priority setting frame generation unit to generate a monitoring start instruction frame that instructs the communication apparatus to start monitoring the traffic after the train is started, cars of the train split, or the cars of the train are combined together,
the priority setting frame generation unit generates the monitoring start instruction frame, and
the output control unit transmits the monitoring start instruction frame to the communication apparatus.
13. The system control apparatus according to claim 12,
wherein
the command unit instructs the priority setting frame generation unit to generate a monitoring end instruction frame that instructs the communication apparatus to finish monitoring the traffic after a predetermined time elapses from the transmission of the monitoring start instruction frame,
the priority setting frame generation unit generates

the monitoring end instruction frame, and
the output control unit transmits the monitoring end instruction frame to the communication apparatus.
14. A train communication system comprising:
the communication apparatus according to any one of claims 2 to 5 and mounted on each car of a train; and
the system control apparatus according to any one of claims 10 to 13.
15. A train communication system comprising the communication apparatus according to any one of claims 6 to 9, the communication apparatus being mounted on each car of a train.
16. The train communication system according to claim 15, further comprising a system control apparatus to generate and transmit a monitoring start instruction frame that instructs the communication apparatus to start monitoring traffic of a low latency frame after the train is started, cars of the train split, or the cars of the train are combined together, and generate and transmit a monitoring end instruction frame that instructs the communication apparatus to finish monitoring the traffic after a predetermined time elapses from the transmission of the monitoring start instruction frame, wherein
the communication apparatus starts monitoring the traffic on the basis of the monitoring start instruction frame and finishes monitoring the traffic on the basis of the monitoring end instruction frame.
17. A communication method of a train communication system
mounted on a train and including a system control apparatus

that generates control frames and a communication apparatus that transfers the control frames, wherein
the control frames include a general frame and a low latency frame that is required to be transferred with lower latency than the general frame, and when the communication apparatus preferentially transfers the low latency frame over the general frame, the communication method comprises:
a first notification frame transmitting step in which the communication apparatus monitors traffic of the low latency frame and, when the traffic is higher than or equal to a predetermined threshold, transmits, to the system control apparatus, a first notification frame indicating that the traffic is higher than or equal to the threshold;
a first priority setting frame transmitting step in which the system control apparatus transmits, to the communication apparatus, a first priority setting frame that is a response to the first notification frame, the communication apparatus having a priority setting table set therein, the priority setting table indicating priority of the control frames and instructing a modification to the priority setting table such that a control frame having low priority among the control frames treated as the low latency frames is treated as the general frame; and
a first priority setting table modifying step in which the communication apparatus modifies the priority setting table on the basis of the first priority setting frame such that a control frame having low priority among the control frames treated as the low latency frames is treated as the general frame.
18. The communication method according to claim 17, further comprising:
a second notification frame transmitting step in which

the communication apparatus monitors the traffic even after modifying the priority setting table and, when the traffic is less than the threshold, transmits, to the system control apparatus, a second notification frame indicating that the traffic is less than the threshold;
a second priority setting frame transmitting step in which the system control apparatus transmits, to the communication apparatus, a second priority setting frame that is a response to the second notification frame and instructs a a modification to the priority setting table such that a control frame having high priority among the control frames treated as the general frames is treated as the low latency frame again; and
a second priority setting table modifying step in which the communication apparatus modifies the priority setting table on the basis of the second priority setting frame such that a control frame having high priority among the control frames treated as the general frames is treated as the low latency frame again.
19. A communication method of a train communication system mounted on a train and including a system control apparatus that generates control frames and a communication apparatus that transfers the control frames, wherein
the communication apparatus has a priority setting table set therein, the priority setting table indicating priority of the control frames,
the control frames include a general frame and a low latency frame that is required to be transferred with lower latency than the general frame, and when the communication apparatus preferentially transfers the low latency frame over the general frame, the communication method comprises:
a first priority setting table modifying step in which

the communication apparatus monitors traffic of the low latency frame and, when the traffic is higher than or equal to a predetermined threshold, modifies the priority setting table such that a control frame having low priority among the control frames treated as the low latency frames is treated as the general frame.
20. The communication method according to claim 19, further comprising
a second priority setting table modifying step in which the communication apparatus monitors the traffic even after modifying the priority setting table and, when the traffic is less than the threshold, modifies the priority setting table such that a control frame having high priority among the control frames treated as the general frames is treated as the low latency frame again.