ieee802.11切換機(jī)制的研究與應(yīng)用

1、南京航空航天大學(xué)碩士學(xué)位論文IEEE802.11切換機(jī)制的研究與應(yīng)用姓名：裴衛(wèi)軍申請學(xué)位級別：碩士專業(yè)：計(jì)算機(jī)應(yīng)用技術(shù)指導(dǎo)教師：陳兵2010-12IEEE 802.11 切換機(jī)制的研究與應(yīng)用 ii ABSTRACT As a perfect combination of computer networks and wireless telecommunication technology, Wireless Lo

2、cal Area Network (WLAN) is gradually used for data communications in rail transit, simultaneously WLAN handoff becomes one of the hottest research issues. Due to the limited WLAN radio power, t

3、he range of radio coverage is within hundreds of meters, and since that vehicle- mounted mobile radio needs frequently handoff in different access points. It will not only cause packet loss, r

4、educing reliability, but can also lead to certain time network outages. So it plays a critical impact on wireless network performance. Firstly this paper introduces the data communication system

5、 in the rail transportation, then gives an overview of IEEE 802.11 WLAN and some limitations in the rail transit, finally analyzes and summarizes the WLAN data link layer handoff research pro

6、gress at home and abroad. Second, in view of the smooth handoff, combined with the common store and forward thinking in wireless network, this paper gets the wireless link events through the

7、 Netlink socket for user and kernel space communication, captures and forwards frames by packet socket, implemented a smooth handoff mechanism on the Linux wireless AP which is independent of d

8、viver. Fping, Ixchariot and other test tools verify that the new mechanism greatly reduces the packet loss rate and improves the network performance. Third, in the fast handoff, the same channe

9、l is used in the track side adjacent AP for the special rail transit circumstances. This paper obtains different BSS’ s beacons by way of modifying MadWifi. Fast handoff is opportunely trigger

10、ed by comparison of RSSI to support stable and reliable link. Extensive experimental results bear out that the handoff delay is less than 20ms. Finally, this paper gives the improved mechanisms

11、 for smooth and fast handoff in the rail transit. In the introduced data communication system framework, the redundancy and retransmission mechanism is adopted to overcome the problem of wireless cha

12、nnel unreliability, at the same time, nil packet loss is achieved; while using wireless admission control, firewall and IPSec policies make up for the open authentication measures in order to