In a wireless mesh network, a battery operated node can select a parent node via which messages are routed to further nodes. The parent node can initially be selected based on signal strength. The node receives acknowledgements for messages sent, if they arrive. The node calculates a reliability indicator of the parent node based on the number of messages for which an acknowledgement has been received. If the reliability indicator exceeds a predetermined threshold the node selects a new parent node, based on second selection criteria. For example, the node with the next greatest signal strength.