Methods and apparatus are described for a navigation system. The members define a projecting annular disc that is received in an annular channel that is filled with hydraulic sealing fluid such as oil. The method includes the first node transmitting a request frame into the LAN, the second node transmitting a reply frame to the first node if receiving the request frame, and the first node checking whether a destination address of the reply frame comprises an address of the first node when receiving the reply frame.