利用IP-Decoupling的方法支援主機行動性

Abstract

這篇論文提出一個利用IP-Decoupling的方式來使主機支援在無線網路上的行動性，本論文提出此方法的設計，實作與效能評估。在目前的網路架構中，網路位址有兩個作用，一個是在底層提供主機的位置資訊，另外一個則是提供主機上層一個獨一無二的識別記號。因為網路位址同時有這兩個作用，使目前的網路協定堆疊並不適合行動網路，因此我們提出IP-Decoupling的方式把目前的網路位址分成兩部分，上層使用的網路位址是用來識別主機，而下層所用的網路位址是用來代表目前所在的位置，並提出一個位址對應表來對應兩個位址。我們也利用了目前的DNS系統和Secure DNS Update來作找尋目前行動主機位置的主要機制，因此本方法並不需要任何特殊的伺服器的幫助即可支援主機行動性。和目前IETF所提出的Mobile IP比較，本方法封包的傳送路徑為最佳化，且改善了Mobile IP的幾個缺點，和Mobile IPv6相比，封包的負擔比較小，因此有較佳的效能。除此之外，本方法幾乎不需要修改就可以使用在IPv6的網路上面，因此可以讓主機在IPv4和IPv6的網路之間漫遊。另外，本方法也可以支援兩個不同網路介面(例如無線區域網路和電話網路)之間的漫遊。

This thesis presents the design, implementation, and performance evaluation of an IP-decoupling (IPD) approach that can support host mobility for wireless Internet. An IP address in the current TCP/IP protocol stack serves dual purposes: a routing directive in the network-layer and an end-point identifier in the transport or upper-layer. This coupling of the routing directive and the end-point identifier makes it difficult or unnatural to support host mobility in Internet. Although IETF has proposed Mobile IP (MIP) to support host mobility, the performance of Mobile IP is still not good enough. Therefore we propose a new IPD approach that can support host mobility by decoupling the IP layer routing directive from the transport layer identification. Similar to MIP protocols, when an MN changes its point of network attachment, the MN will obtain a new IP address as its new care-of address (COA) in IPD approach. However the MN uses secure DNS updates, instead of MIP registration messages, to inform the home domain DNS of the changes in care-of IP addresses. As a consequence, the IP routing directive of the MN can be acquired through a normal DNS query. Besides, each IPD-capable host is equipped with an address map table (AMT) to record the bindings between IP-layer routing directives and transport-layer identifiers. The binding information of AMT can be updated through ICMP message exchange directly between two communication peers with without the support of a third party. Therefore the routing path of the IPD approach is always optimized as it is in Mobile IPv6. Analysis results also show that the packet overhead in IPD approach is lower than that in both Mobile IPv4 and IPv6. Besides, the IPD approach can be easily adopted, with little modification, to support host mobility in IPv6 networks, or IPv4 and IPv6 co-existed networks. Furthermore, IPD approach can also be used to support mobility in an overlaid wireless network such as a wireless LAN/GPRS two-tier wireless network.