The emergence of packet loss is inevitable because of the BSS handoff in IEEE 802. 11 networks, which generates great impact on the network performance and limits the development of WLANs in the mobile environment. In order to reduce packet loss, this paper presents a data link layer smooth handoff mechanism triggered by wireless events. And we realize the scheme on the embedded Linux wireless access point in the user space. The extensive experimental results show that, the method can largely reduce the packet loss ratio and improve the network performance within the permissible delay, without changing the current IEEE 802. 11 protocol. The mechanism is independent of the driver, features good portability, so that it can be incrementally added on the existing Aps without changing STA, and reduces the upgrade cost.%IEEE 802.11网络中的BSS切换不可避免地产生丢包问题,这会造成网络性能严重下降,进而限制了移动环境下WLAN的广泛应用.为了降低切换过程中的丢包率,本文提出了一种在数据链路层、由无线链路事件触发的用户空间平滑切换机制,并且在基于嵌入式Linux平台的无线AP上进行了实现.大量的实验结果表明,在无需对当前IEEE 802.11协议进行改动的前提下,新切换机制可以保证在允许的时延范围内,较大地降低丢包率,提高网络性能,并且可以支持平滑漫游.改进的平滑切换机制独立于驱动,具有良好的可移植性,可以在现有AP上增量添加,而无需更改STA,降低了升级成本.
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