Abstract: In the software defined wireless network (SDWN),mobile terminal are likely to cause network interruption and improper selection of awaiting switched wireless access point (AP) during the handoff process,which may result in a significant decrease in real-time application service quality.In order to address this issue,this paper proposes an AP handoff scheme based on dual network interface controller (NIC) mutual backup.This scheme uses the dual-NIC mutual backup mechanism to realize the soft handoff at link layer.The mobile terminal can associate with the new AP first and then disassociate from the old AP.Further,the network address translation (NAT) mechanism is adopted in SDWN to realize seamless handoff at network layer.Inspired by the technique for order preference by similarity to an ideal solution (TOPSISI),the proposed AP selection algorithm constructs the candidate object to be evaluated according to the signal strength,load,transmission bandwidth and the current connections numbers of candidate APs.The AP selection are made based on the calculated closeness between the object to be evaluated and the ideal object.Finally,the experiments are conducted on NS-3.The results show that compared with the RSSI based handoff scheme,the transmission delay and the packet loss rate of the proposed scheme are reduced by 85.29% and 14.11% respectively,and the throughput is increased by 8.94%.The proposed dual-NIC mutual backup handoff scheme can significantly improve the problem of network interruption caused by AP handoff in the single-NIC handoff scheme,and better guarantee the service quality of real-time applications.

Key words: Access point handoff, dual-NIC, Soft handoff, Software defined wireless networks, TOPSIS