When a packet received from a ring network is addressed to a device on a local network established under a transmission apparatus, then that transmission apparatus detects whether a memory device installed therein is in the memory full state. If the memory device is determined to be in the memory full state, then the transmission apparatus sends the packet, which was received from the ring network, back to the ring network. Subsequently, when the memory device recovers from the memory full state, the transmission apparatus sends the packet to the specified device in the local network.