To overcome the problems with their original WLAN and reap the potential benefits listed earlier earlier in this case study, ST. Luke's made two changes[CONR03]. First, the hospital phased out the Proxim APs and replaced them with Cisco Aironet (WWW.aironet.com) APs. The Cisco APs, using IEE 802.11b, operate at11Mbps. Also, the Cisco APs use direct sequence spread spectrum (DSSS), which is more reliable than the frequency-hopping technique used in the Proxiom APs. The second measure taken by St Luke's was to acquire a software solution from NetMotion Wireless(netmotionwireless.com) called Mobility. The basic layout of the Mobility solution is shown in Figure V.1. Mobility software is installed in each wireless client device (typically a laptop or handheld) and in two NetMotion servers whose task is maintain connections. The two severs provide a backup capability in case one sever fails. The Mobility software maintains the sate of an application even is a wireless device moves out of range, experiences interference, or switches to standby mode. When a user comes back into ranger or switches into active mode, the user's application resumes where it left off. In essence, Mobility works as follows. Upon connecting, each Mobility client is assigned a virtual IP address by the Mobility server on the wired network. The Mobility sever manages network traffic on behalf of the client, intercepting packets destined the client's virtual address and the client, intercepting packets destined for the client's virtual address and forwarding them to the client's current POP (point of presence) address. While the POP address may change when the device moves to a different subnet, from one converage area to another, or even from one network to another, the virtual address remains constant while any connections are active. 是先用DR.EYE跑过一次.... 已经修改过很多~.~ DR.EYE跑完的结果根本不能看 --

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