| Summary: | 碩士 === 國立雲林科技大學 === 電機工程系碩士班 === 94 === In IEEE 802.11 networks, the handoff process occurs when a station moves its association from one access point (AP) to another. Handoff involves AP discovery, authentication, reassociation establishment, and possible inter-AP transfer of physical connectivity and context like quality of service parameters or credentials specific to the mobile station. For secure context exchanges along with authentication and cryptographic key management, the IEEE 802.1X framework has been adopted as mandatory part of Robust Security Networks. Provided IEEE 802.1X transactions at a remote site, internetwork operations account for another potentially prohibitive handoff delay.
For the provisioning of fast handoff support, current schemes preauthenticate a mobile station or distribute the context of the station proactively to neighboring APs. Each target AP caches the station’s context a priori and can thus bypass IEEE 802.1X authentication if the station reassociates. We present an approach independent of any well-known schemes to improving caching effectiveness that allows for both recency information and distinct cache miss penalty indicative of authentication delay. These metrics form a means to assess the relative importance of each context among all the contending contexts. We assign longer cache lifetime (called Time-to-Live value in this text) to high-penalty contexts such that these contexts become less volatile, whereas low-penalty data shorter lifetime. In consequence, low-penalty contexts are more likely to expire and can thus make room for caching other new contexts without overriding the storage space of high penalty contexts. This enables high-penalty stations to receive fewer cache misses upon reassociations. An underlying idea is that frequent high-penalty cache misses by reassociating stations impairs the handoff process and hence should be avoided. Performance results show that our approach outperforms counterpart schemes generally by over 15%~35% in terms of handoff delays when the ratio of cache capacity to station population is small. Our development lends itself to the emerging IEEE 802.11r standard in support of fast Basic Service Set transitions.
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