在行動IP(Mobile IP)中，當移動節點(Mobile Node)離開內部網路(Home Network)不改變其內部位址(Home Address)，必須透過註冊讓內部代理人(Home Agent)來掌握移動節點的動向。移動節點於外部代理人(Foreign Agent)間移動時因註冊所產生的註冊控制訊息，會對整個網路產生不小的負擔，尤其當移動節點數目多且快速於代理人間移動時。於是行動IP區域註冊(Mobile IP Regional Registration)的機制被用來降低換手延遲(Handoff Latency)及降低註冊訊息(Signaling Cost)。在這個機制下，家註冊(Home Registration)的成本遠比區域註冊來的大，於是減少家註冊的發生次數，是降低訊息成本的最主要方法。即使如此，這樣的機制由於必須預先制定區域領域(Regional Domain)，對於瞬息萬變的無線網路常有因為分割不當及考慮不夠全觀導致效能降低的缺點。
　　我們提出一個以外部代理人的工作量以及移動節點行為當作領域分割依據的方法。統計一段時間內整個網路裡所有移動節點在外部代理人上造成的工作量。以上述統計資料為參數，進而推算每個區域領域的訊息成本，並尋找鄰近可使訊息成本下降的領域以進行合併，如此反覆直至沒有任何的領域可以被合併且訊息成本無法再下降為止。在我們方法裡，使用一中央集權式的計算方式，其與針對每個使用者的區域分割方式，最大不同在於不用使移動節點承擔額外的計算負擔，對於現實的使用上較為合理。除此之外中央集權式的計算方式期望在制定領域時可以考慮到整個網路的狀態以使成本可以降至最低。於是對於行動IP區域註冊的使用效能上可以大幅提升。

　　In Mobile IP, when a mobile node leaves its home network and do not want to change its home address, it must notify its home agent to update its location by registration to its home agent. Since the mobile nodes must register their location after every movement, the registration controlling messages will result in heavy traffic overheads especially when there are large amount of mobile nodes and each mobile node fast roams among foreign network. Therefore, the mobile IP regional registration was proposed to reduce handoff latency and signaling cost by registering in the regional domain. Because the cost of the home registration is much greater than that of the regional registration, decreasing the frequency of home registration is the main idea to reduce the signaling cost. Even for this mechanism, due to regional domains are fixed a priori, it is neither adaptive to the transitory wireless network nor conscientious to the overall network states and therefore may lead to performance reduction.
　　We propose an approach, which adaptively determines the suitable regional domain according to workload statistics of foreign agents and behavior of mobile nodes. First, we define a protocol to collect the statistical information of foreign agents. The statistics of the resource utilization and the mobility of mobile nodes are used to calculate the signaling cost of each regional domain. The foreign agents aggregate as clusters to form suitable domains if the aggregation leads to a lower signaling cost. Iteratively, as performing the aggregation process, we can obtain a low signaling cost network. In our scheme, we use a centralized architecture to construct the regional domain. The primary difference from the distributed method is that the mobile nodes do not bear the overhead of determining its domain and thus the proposed approach is more reasonable for real world implementation. In this way, the overall network states are considered in regional domain determination so that the signaling cost of network is dramatically reduced and the performance of mobile IP regional registration scheme is improved.

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[2] Eva Gustafsson, Annika Jonsson, Charles E. Perkins, “Mobile IPv4 Regional Registration” draft-ietf-mobileip-reg-tunnel-08.txt, November 2003
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