移動式 IP 和無線網路之整合與實作

Abstract

Mobile IP通訊協定已經被廣泛的使用在支援無線網路上的 IP 可移動特性。 其功能為當一個使用者從一個子網域移動到另一個子網域時，此通訊協定可保持連線的不被中斷。另一個日漸得到注意的網路架構為可移動式無線隨意網路，(俗稱 MANET)，此能很有彈性的被使用在任何環境中而並不需要基地台的支援就能運作。為了轉移到 All-IP 的環境，將這兩種架構整合起來是一種抵擋不住的趨勢。 在這本論文中，我提出如何將固有的無線基地台架構延伸到多個可移動式無線網路叢集架構 (其每個都是 Internet 上的一個子網域)，以及討論如何在此環境上支援 Mobile IP 通訊協定。這種整合有利於兩個方面：從 Mobile IP 的角度上看來，遠端代理人 (Foreign Agent) 的服務範圍可以不再被侷限在只有直接相連的使用者身上而得以延伸出去。而從無線隨意網路的角度上看來，使用者可以直接享受到目前 Internet 現有的總總服務。這篇文章報告了我們在 IEEE 802.11 無線網路上整合以及實作的經驗。提出來的一些問題包括兩兩 MANETs 的重疊關係，如何可以動態的調整可移動式代理人 (Mobile Agent) 的服務範圍大小，有限制的的廣播以及各種不同的通訊路徑選擇方案。同時也討論了如何調整 Mobile IP 和在網路架構第二層和第三層實做的優點和缺點。最後列出了一些對於我們系統所做的的效能測試。

Mobile IP has been widely accepted as a standard to support IP mobility in a wireless Internet environment to keep a session connected when a mobile host roams from subnet to subnet. Another emerging wireless network architecture that is gaining more and more popularity is the {\it mobile ad hoc network (MANET)}, which can be flexibly deployed in almost any environment without the need of infrastructure base stations. In order to move to an all-IP environment, there seems to be growing demand to integrate these two architectures together. In this paper, we propose to extend the typical {\it wireless access points} to multiple clusters of MANETs, each as a subnet of the Internet, and discuss how to support Mobile IP in such environment. Such integration is beneficial to both societies. From Mobile IP's prospective, Foreign Agents' service areas are not limited to hosts within a single (wireless) hop any more. From MANET's prospective, mobile hosts can immediately enjoy tremendous services already existing on the Internet. This article reports our integration and implementation experience based on IEEE 802.11b wireless LANs. Issues such as overlapping of MANETs, dynamic adjustment of mobile agents' service coverages, support of local broadcast and various communication scenarios are addressed. Discussion also covers required adjustments of Mobile IP and pros and cons of layer-2 and layer-3 implementation of MANETs. Performance results are also reported.