支援WiMAX網路快速換手之分散式金鑰配置機制

Abstract

本論文依據IEEE802.16e與WiMAX Forum中Network Working Group (NWG )制定的換手協定，修改換手過程時的金鑰派送與傳送機制，以減少WiMAX後端網路的負擔為目標，達到快速換手的目的。 IEEE802.16e的換手程序包含金鑰的重新派送，因此NWG也定義了後端(backhaul)網路產生與派送金鑰的金鑰更新機制。也就是說，每次的換手程序都必定在後端網路執行一次金鑰的產生及派送的動作。這樣的作法不僅會增加後端網路的負擔，更新金鑰的動作也會增加換手延遲。 針對此問題，本論文提出一個分散式的金鑰配置機制，在不失安全性的前提下，藉由擴大金鑰有效範圍，減少了換手過程中執行金鑰產生與派送程序的次數，藉以減少換手時所產生的後端網路資訊量。也因此，改善了換手程序所需的平均換手時間。 最後，本論文也進一步分析及探討我們提出的方法的安全性，確定此方法在運作上不失其安全性；另一方面，本論文也利用數學分析，比較此方法與NWG所制定的方法，證明了本論文的方法在減少網路負載上較為優異，也因此改善了換手程序所需的平均換手時間。

This thesis proposes a distributed key assignment mechanism that can support fast handover for WiMAX networks. According to the specifications of IEEE 802.16e and Network Working Group (NWG) of WiMAX forum, a WiMAX mobile station (MS) needs to perform a key re-assignment for each handover procedure. The key re-assignment procedudre requires several message exchanges between the MS and the authentication server situated in the backhaul network. Therefore, it not only introduces signal overhead to the backhaul network but also increases the latency of handover procedures. The underlying concept of the distributed key assignment mechanism is to enlarge the scope of the authentication key (AK) so that the MS needs not perform an AK re-assignment each time it roams from one base station to another. By reducing the number of key re-assignments, the proposed mechanism can reduce both the number of signals in backhaul networks and the handover latency, while retaining the same security level as the original WiMAX does. We also present an analytical model to evaluate the proposed key assignment mechanism. Analytical results show that the proposed mechanism can not only reduce signal overhead in backhaul networks but also shorten the handover latency. Furthermore, we also analyze the security level of the proposed mechanism to justify the effectiveness of the proposed mechanism.