This read-only enumerated value reports the cause of an OpenFlow connection state change, with tcpDown(1) meaning the underlying TCP session dropped, heartbeatTimeout(2) meaning OpenFlow keepalive messages stopped arriving in time, pduError(3) meaning a malformed OpenFlow protocol message was received, and connectionUp(4) meaning the connection is actually up. Admins use this to quickly triage why a switch lost its controller connection without having to dig through packet captures first. For example, a value of heartbeatTimeout(2) would point an admin toward network congestion or controller overload rather than a hard link failure, which tcpDown(1) would suggest instead.