This read-write INTEGER specifies the timeout, in milliseconds, for acknowledgment of a control-plane message sent to another node. An administrator uses this as the base retransmission timer governing how long the node waits for an ack before considering a control-plane message unacknowledged. For example, a shorter timeout makes the node detect unacknowledged messages to unresponsive nodes faster, at the risk of retransmitting prematurely to nodes that are simply slow to respond.