A bridge-based RAS backbone network system and a signal processing method therefor are provided. In the bridge-based RAS backbone network system, a plurality of BSBs with Layer 2 (L2) switches are connected to a plurality of RASs, and a plurality of SCBs with L2 switches are connected to part of the BSBs in a lower layer, forming a core network. An HLR manages configuration information of network entities by storing the IP addresses and MAC addresses of MNs within the network and the addresses of SCBs to which the MNs belong in a table. Each of the SCBs statically preserves the MAC address of an external default router, for relaying an egress frame, statically registers its individual MAC address in other SCBs in the core network beforehand, detects a destination MN through the HLR, and sends a frame to the SCB of the destination MN or the MAC address of the external default router.