Communication apparatus, communication system, communication method, and computer readable medium

A communication system comprising a plurality of communication apparatuses that selects, from the plurality of communication apparatuses, a grandmaster that is to be a standard of time of the plurality of communication apparatuses, wherein

• a device configured as one of the plurality of communication apparatuses includes processing circuitry
• to obtain from a new communication apparatus not part of plurality of communication apparatuses, a grandmaster mediation message that is a grandmaster mediation message used for selecting the grandmaster and that includes an assigned priority of the new communication apparatus, and to verify whether or not the priority of the new communication apparatus is higher than an assigned priority of a current grandmaster, and
• when the priority of the new communication apparatus is verified as being higher than the priority of the current grandmaster, by
• obtaining a synchronization message including a time of the new communication apparatus from the new communication apparatus before switching the grandmaster to be the new communication apparatus,
• calculating a difference between the time of the other communication apparatus and a time of the device, and when the difference is less than a threshold, perform mediation to switch the grandmaster to be the new communication apparatus, and
• when the difference is more than or equal to the threshold, either (1) ignore the synchronization message from the new communication apparatus thereby preventing mediation to be performed to switch the grandmaster to be the new communication apparatus, or (2) cause the new communication apparatus to synchronize time with the current grandmaster before performing mediation to switch the grandmaster to be the new communication apparatus.

A communication method of a device configured as one of a plurality of communication apparatuses that are included in a communication system that selects, from the plurality of communication apparatuses, a grandmaster that is to be a standard of time of the plurality of communication apparatuses, the communication method comprising:

• obtaining from a new communication apparatus not part of the plurality of communication apparatuses, a grandmaster mediation message that is a grandmaster mediation message used for selecting the grandmaster and that includes an assigned priority of the new communication apparatus, and verifying whether or not the priority of the new communication apparatus is higher than an assigned priority of a current grandmaster;
• and
• when the priority of the new communication apparatus is verified as being higher than the priority of the current grandmaster, by
• obtaining a synchronization message including a time of the new communication apparatus from the new communication apparatus before switching the grandmaster to be the other communication apparatus,
• calculating a difference between the time of the new communication apparatus and a time of the device, and when the difference is less than a threshold, performing mediation to switch the grandmaster to be the new communication apparatus, and
• when the difference is more than or equal to the threshold, either (1) ignoring the synchronization message from the new communication apparatus thereby preventing mediation to be performed to switch the grandmaster to be the new communication apparatus, or (2) causing the new communication apparatus to synchronize time with the current grandmaster before performing mediation to switch the grandmaster to be the new communication apparatus.

A non-transitory computer readable medium storing a communication program of a device configured as one of a plurality of communication apparatuses that are included in a communication system that selects, from the plurality of communication apparatuses, a grandmaster that is to be a standard of time of the plurality of communication apparatuses, the communication program causing the device that is a computer to execute:

• a priority verification process to obtain from a new communication apparatus not part of the plurality of communication apparatuses, a grandmaster mediation message that is a grandmaster mediation message used for selecting the grandmaster and that includes an assigned priority of the new communication apparatus, and to verify whether or not the priority of the new communication apparatus is higher than an assigned priority of a current grandmaster;
• and
• a mediation process, when the priority of the new communication apparatus is verified as being higher than the priority of the current grandmaster,
• to obtain a synchronization message including a time of the new communication apparatus from the new communication apparatus before switching the grandmaster to be the new communication apparatus,
• to calculate a difference between the time of the new communication apparatus and a time of the device,
• when the difference is less than a threshold, perform mediation to switch the grandmaster to be the new communication apparatus, and
• when the difference is more than or equal to the threshold, either (1) ignore the synchronization message from the new communication apparatus thereby preventing mediation to be performed to switch the grandmaster to be the new communication apparatus, or (2) cause the new communication apparatus to synchronize time with the current grandmaster before performing mediation to switch the grandmaster to be the new communication apparatus.