Communication system

A communication system comprising:

• a plurality of communication nodes that relay a fault diagnosis communication of a diagnosis request and a diagnosis result between a request source of a fault diagnosis and a request destination of the fault diagnosis, wherein:
• any one of the communication nodes includes:
• a communication determination unit configured to determine whether a present communication is the fault diagnosis communication;
• and
• a communication setting unit configured to increase a priority of a priority parameter indicating the priority of communication when the communication determination unit determines that the present communication is the fault diagnosis communication either one of when the request source transmits the diagnosis request to the request destination or when the request destination transmits the diagnosis result to the request source;
• the any one of the communication nodes is defined as a first communication node;
• the communication determination unit is defined as a first communication determination unit;
• the communication setting unit is defined as a first communication setting unit;
• the first communication setting unit is configured to increase the priority of the priority parameter when the first communication determination unit determines that the present communication is the fault diagnosis communication either one of when the request source transmits the diagnosis request to the request destination or when the request destination transmits the diagnosis result to the request source;
• another one of the communication nodes different from the first communication node is defined as a second communication node;
• the second communication node includes:
• a second communication determination unit configured to determine whether the present communication is the fault diagnosis communication;
• and
• a second communication setting unit configured to decrease the priority of the priority parameter that the first communication setting unit has increased when the second communication determination unit determines that the present communication is the fault diagnosis communication either one of when the request source transmits the diagnosis request to the request destination or when the request destination transmits the diagnosis result to the request source.