隨著無線通訊的服務近年來越來越受到注目，使用者對於即時應用的需求也隨著蓬勃成長。然而，行動網路要達到廣泛的應用依然有許多技術問題需要克服。在IP網路中，封包係透過IP位址來轉送到目的地，這個特性使得使用者在行動網路中漫遊時，會因為IP位址的改變而形成某些換手(handover)上的問題，特別是換手的延遲(handover latency)。
行動IP (Mobile IP)即是設計來解決此類的問題。然而IPv6為避免IP位址衝突，會進行重覆位址偵測(duplicate address detection, DAD)的機制，而這項動作花費的時間，這對許多即時性的應用而言，將會造成嚴重的延遲現象。為了縮短MIPv6應用在換手時的延遲，有專家提出預先重覆位址偵測(advanced DAD, aDAD)之技術，能夠省略了重覆位址偵測的步驟，進而大幅減少了IPv6在換手上的延遲。
本研究目的在於改進aDAD的換手協定，主要是減少移動節點在提出換手要求後，換手訊息在基地台之間傳遞與處理的時間，如此一來，待移動節點提出換手的要求後，即可以更快地得到能夠在下一個子網路使用的IP位址。
研究將利用Network Simulator version2 (NS2)程式來進行新協定的模擬，並針對換手延遲、連線的吞吐量（throughput）等評量指標，來比較本研究所提出之協定與原始預先重覆位址偵測在換手延遲的差別。

While wireless technology is more and more popular nowadays, there are still some technical obstacles that must be overcome before mobile networking can become wide-spread.
Mobile IP technology is used to maintain users’ network connections when mobile hosts are traveling between different subnetworks. However, in order to avoid the address collisions, MIPv6 must perform the address duplicate detection (DAD). The DAD procedure is defined in RFC 3775 standard and is a time-consuming task. Although techniques such as advanced DAD (aDAD) and optimistic DAD (oDAD) have improved this latency, both methods have limitations.
In this thesis, we enhance aDAD handover protocol by reducing the delay while handover messages are exchanged between base stations. Therefore, mobile users can immediately receive responds from serving-router after they make their requests to handover to new subnetworks.
We use the “Network Simulator version 2” to evaluate the performance of the proposed mechanism. Furthermore, we set up different simulation scenario to compare the handover performance of our mechanism in this thesis with the ordinary aDAD handover strategy.

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