Integrating Inter Access Points Protocol and Enhanced Distribution Coordination Function to Enhance the QoS of Voice over IP in Wireless LAN
| Autor: | Wan-wei Huang, 黃宛薇 |
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| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 Seamless multimedia applications, such as VOIP, video conferencing and video on demand, and mobility make the WLANs have a numerous up-growth in market. With extensive deployment of WLANs, the ubiquitous services can be achieved to support more and more convenient access to Internet. In WLANs the mobile users may roams between APs. To remain the application, MN has to maintain a connection from one AP to another AP, which is the procedure of handoff. The IEEE 802.11f specifies the inter access point protocol (IAPP) to handle the handoff procedure. However, the higher IAPP handoff latency due to the hard handoff characteristics, before make the connection with the new AP the MN first disconnects with the old AP, could reduce the mobility of mobile users. There are three stages to complete the IAPP handoff: scanning, authentication, and re-association. The scanning stage takes the major handoff latency which is about 350ms which is not satisfied the QoS requirements of real time applications. In this thesis, we try to reduce the handoff latency to less than 52ms in the best case to closely match the QoS requirements of the VOIP applications in WLANs. The proposed method integrates enhance IAPP, neighbor table, and RSSI triggering handoff. The use of neighbor table can reduce the scanning latency because the numbers of probable channels to be scanned are less than that of IAPP. However, in the beginning of operation, the null neighbor table will cause a longer scanning latency which leads mismatch the QoS requirements. To reduce the warm-up stage failure, we recommend a pre-operation training or a manual handle to build the neighbor table. The enhanced IAPP has small authentication and re-association latency than that of IAPP. These characteristics make the proposed method reduces the handoff latency to less than 52 ms in the best case. In the future, we try to make up simulation environment in ns-2. This is a huge job including build up the enhance IAPP module, neighbor table client and server, RSSI triggering handoff, and so on. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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