Switch device and communication control method

A communication control method in a switch device to be mounted on a vehicle and having a buffer for holding communication data to be relayed, comprising:

• relaying communication data communicated between a plurality of communication devices, and
• transmitting stop request to at least one communication device of the plurality of communication devices if communication data to be transmitted to a device in which abnormality has been detected is held in the buffer, the stop request requesting for stopping transmission of communication data to the switch device and requesting for holding of communication data to be transmitted to the switch device and the one communication device being located on a path from the switch device to a transmission source of the communication data and being mounted on the vehicle.

(canceled)