Handoff procedure in IEEE 802.11 wireless networks must be accomplished with as little interruption as possible to maintain the required quality of service (QoS). We have developed a fast handoff scheme, called AuthScan, to provide a novel usage of the open system authentication phase to reduce channel scanning latency. AuthScan comprises two steps: firstly, a client caches its handoff history with beacon information. Secondly, when in need of handoff, a client transmits authentication request frames to the selected access points (APs) from the cache instead of broadcasting probe request frames as in active scan to discover the available APs. The next AP is selected by comparing quickly acquired handoff metrics during the handoff procedure. This fast handoff is possible by upgrading only software on the client side. This paper presents the theoretical handoff latency of AuthScan in comparison with other approaches, and shows the effectiveness of our system through implementation and experiments.

We have developed a fast handoff scheme, called AuthScan, to reduce the time-consuming channel scanning latency in IEEE 802.11 wireless networks. AuthScan comprises two steps: First, a client caches its handoff history with beacon information. Second, when in need of handoff, a client transmits Authentication Request frames to the selected Access Points (APs) from the cache instead of broadcasting Probe Request frames in active scan to discover the next AP. Our proposed method does not require any support from the infrastructure network and contributes to finish the handoff procedure with the lowest latency when compared to approaches that improve the efficiency of channel scanning. Furthermore, AuthScan requires neither hardware upgrades to the client, nor any modification to currently deployed APs. In this paper, we present the theoretical handoff latency of AuthScan and compare it to other approaches.

Handoff process in IEEE 802.11 wireless networks must be accomplished with as little interruption as possible to maintain the required quality of service (QoS). Previous research reported that channel scanning phase accounts for more than 90% of the overall link-layer handoff latency, ranging from 350 to 500 msec. In order to eliminate the time-consuming channel scanning latency we propose a stand-alone, shared beacon channel, where stations (STAs) can update information about neighboring access points (APs) via an extra receiver. Our proposed method contributes to completely eliminate the channel scanning phase, therefore, realizing fast handoff in IEEE 802.11 wireless networks. In this paper, we implement our proposed method on FreeBSD 6.1R kernel with Atheros AR5212-based 802.11 a/b/g chipsets. From experimental results, we find that it takes 6.063 msec delay on average during handoff from 802.11b AP to 802.11a AP while transmitting/receiving 480 byte ICMP frames with an interval of 10 msec.

The current channel scanning phase in IEEE 802.11 Wireless LAN does not fit fast handoff due to the following two reasons. First, IEEE 802.11 Wireless LAN operates based on CSMA/CA. Unlike cellular system, STAs can not scan other channels while exchanging data frames with currently associated AP, because it would directly cause frame loss. To attack this problem, related works have tried to utilize Power Saving Mode (PSM) or multiple NICs. Second, beacon interval is too far apart for fast handoff (100 msec by default). Since an STA lacks knowledge about which channel its nearby APs are operating on, it should redundantly scan every single channel regardless whether any AP exists on that channel. Though shorter beacon interval or active scan enable an STA to locate its nearby BSSs more quickly, these approaches increase extra traffic to the limited bandwidth. Previous works tried to provide an STA with nearby AP information approximated by APs collaboratively.