Created by Neevia Personal Converter trial version Improving the latency of 802.11 Hand-offs using Sentinel based Architecture

The IEEE 802.11 based wireless networks have seen rapid growth and deployment in the recent years. WLAN based networks have been deployed in many enterprises and for public Internet access services. Critical to the 802.11 MAC operation, is the hand-off function which occurs when a mobile node moves its association from one access point to another. The small cell size of WLAN creates frequent hand-offs for mobile users. Multimedia and Voice applications require hand-offs between access points to be fast to maintain the quality of the connections. Previous studies have shown that the latency of these hand-offs are high which is dominated by the scanning phase where the client scans to discover the candidate set of next access points. In this paper, we present a sentinel based approach to reduce the scanning latency. Sentinels are stationary nodes in the network which monitors the WLAN continuously. During hand-off the client probes the sentinel to get the minimal set of channels to scan. The sentinels provide the client with a list of channels which is sorted on the best AP the client can associate with at that point of time. The APs are sorted based on the neighbor graph, the client’s current location, the nearest hand-off points and the AP load which is continuously monitored by the sentinels. Our simulation results show that, about 90 % of the time, the client associates with the first AP on the sorted list provided by the sentinels