18.2.Tunnel/Mirror (TCP) Connections for Slow Networks

The OPC DataHub uses a heartbeat to determine the status of the network connection. The tunnel/mirror slave sends a special heartbeat message to the master at specified time intervals, to detect network failures. If the master does not respond within a certain timeout period, the slave changes the status of its connection to Disconnected and attempts to reconnect.

The timout value is usually at least twice the heartbeat rate, and the default setting is five times the heartbeat rate. However, if you have a very slow or irregular network connection, the best thing to ensure that the connection remains open is to override the DataHub timeout, and use the TCP timeout mechanism. It takes longer to detect a network failure, because it waits as long as the TCP stack waits. It means the slowest recognition of a broken link, but doesn't give up until TCP says the link is really dead.

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