| Summary: | 碩士 === 國立交通大學 === 電機資訊學院碩士在職專班 === 93 === As WLAN gets more and more popular, many cities have been set up the dense wireless network. Therefore, WLAN have gradually joined to people’s life. One of the application is Voice Over WLAN. However, most of the application are using the structure of VoIP. Hence, it is very important and indispensability for WLAN industry to overcome how to keep the network stable and how to roam between two base stations or different networks.
In this paper, we will bring up a kind of structure. That will help the wireless LAN company to solve the roaming problem. The wireless LAN module will solve the roaming in Layer2 and Layer3. First of all, we build up the connection by Semi-Soft in wireless LAN module that could help the message exchange in advance in Layer2 and Layer3 when the module starts roaming. In addition, we also create the NAT transformation in WLAN module. It could fix the up layer’s network IP and the application function does not need to change network IP for rebuilding network.
Although we can use Semi-Soft to exchange the information in Layer 2 and Layer 3 beforehand, we just have one real hardware module. It means we just can connect only one AP at the same time. For this reason, when the packet cycle is less than 20ms, the roaming will have delay problem. Nevertheless, if we focus our application on VoIP which packet cycle more than 50ms, the idea is sufficient.
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