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FastScan: a handoff scheme for voice over IEEE 802.11 WLANs

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Abstract

IEEE 802.11 Wireless LANs are increasingly being used in enterprise environments for broadband access. Such large scale IEEE 802.11 WLAN deployments implies the need for client mobility support; a mobile station has to be “handed off” from one Access Point to another. Seamless handoff is possible for data traffic, which is not affected much by the handoff delay. However, voice traffic has stringent QoS requirements and cannot tolerate more than 50ms net handoff delay. The basic IEEE 802.11 handoff scheme (implemented in Layers 1 & 2) only achieves a handoff delay of 300ms at best, leading to disrupted connectivity and call dropping. The delay incurred in scanning for APs across channels contributes to 90% of the total handoff delay. In this paper, the FastScan scheme is proposed which reduces the scanning delay by using a client-based database. The net handoff delay is reduced to as low as 20 ms for IEEE 802.11b networks. We next suggest “Enhanced FastScan” that uses the direction and relative position of the client with respect to the current AP to satisfy the latency constraint in IEEE 802.11a scenarios, which have significantly higher scanning delays due to the larger number of channels. The proposed schemes do not need any changes in the infrastructure (access points) and require only a single radio and a small cache memory at the client side.

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Acknowledgments

This work was supported in part by NSF Award CRI CNS 0551686. The authors would like to thank Dr. Tom Henderson for his support and assistance in implementing the 802.11 infrastructure model in ns-2 as well as the many helpful feedback from the ns-2 developers and user community.

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Authors and Affiliations

  1. Cisco Systems, San Jose, CA, 95134, USA

    Ilango Purushothaman

  2. Department of Electrical Engineering, University of Washington, Seattle, WA, 98195, USA

    Sumit Roy

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  1. Ilango Purushothaman
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  2. Sumit Roy
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Correspondence to Ilango Purushothaman.

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Purushothaman, I., Roy, S. FastScan: a handoff scheme for voice over IEEE 802.11 WLANs. Wireless Netw 16, 2049–2063 (2010). https://doi.org/10.1007/s11276-010-0243-5

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  • DOI: https://doi.org/10.1007/s11276-010-0243-5

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