A signal processing method in a bridge-based RAS backbone network system is provided, in which an MN within a network periodically transmits to an HLR a route-update message for registration updating, if the MN is in active mode and transmits to the HLR a paging-update message having a transmission period longer than that transmission period of the route-update message, for registration updating, if the MN is in idle mode, each of bridges and the HLR stores location information about the MN in a soft state with an age set for the location information in a routing cache according to the route-update message received from the MN, and each of BSBs, SCBs, and an SIB selected from a plurality of SIBs stores location information about the MN in a soft state with an age set for the location information according to the paging-update message received from the MN.