Patent ID: 8805997

Claim:
A communication apparatus comprising: a trunk line communication unit to transmit and receive data to and from an other communication apparatus, the trunk line communication unit comprising: a transmission unit to transmit an effectiveness notification representing that communication is effective to the other communication apparatus; and a reception unit to receive the effectiveness notification from the other communication apparatus; and a control unit to stop part or all of the communication with the other communication apparatus when an abnormality in the communication with the other communication apparatus is detected by not having received the effectiveness notification from the other communication apparatus or by having received abnormality information from the other communication apparatus; wherein: the communication apparatus detects the abnormality in a communication with the other communication apparatus based on whether the effectiveness notification is received from the other communication apparatus or not; the transmission unit transmits the abnormality information representing that the abnormality is detected and information representative of an abnormality condition of the communication to the other communication apparatus together with the effectiveness notification when the abnormality in the communication with the other communication apparatus is detected; the transmission unit transmits information for changing a communication path with a third communication apparatus when the abnormality in the communication with the other communication apparatus is detected; the trunk line communication unit has a plurality of communication units defined as either upstream or downstream on the communication path, and separately transmits and receives data to and from other communication apparatuses; and when an abnormality in a communication with a communication apparatus on the upstream side is detected or when the abnormality information received together with the effectiveness notification through a first communication unit on the upstream side represents that an abnormality is detected, the transmission unit transmits a master candidate notification to a communication apparatus on the downstream side through a second communication unit on the downstream side in order that its own communication apparatus becomes a specific communication apparatus serving as a starting point on the communication path, and when an abnormality in a communication with the communication apparatus on the downstream side is detected or when the abnormality information received together with the effectiveness notification through the second communication unit represents that an abnormality is detected, the transmission unit transmits a response to the master candidate notification to the communication apparatus on the upstream side through the first communication unit in order that its own communication apparatus becomes a termination point on the communication path.