衛星電腦網路中連線指定與尋找傳輸路徑的方法

Abstract

對於太空電腦網路的建構，已建議採用具封包轉換技術的先進通訊衛星． 一般的同步衛星雖然較容易管理，但由於距離很遠，傳輸延遲很長，無法 滿足即時傳輸應用的需求，因此改採用低軌道 (LEO) 衛星以縮短延遲時 間．由於LEO 衛星的軌道較低，因此無法再與地球同步，而網路架構也隨 時在改變，所以衛星間通訊連線的距離並不固定，且連線也常會因地球的 阻隔而被切斷．因此需常常重新連線以維護整個網路架構．這種連線指定 的問題只出現在LEO 衛星網路上．在一個網路中，如果有很多衛星，且每 個衛星均裝備多個通訊連線器，則在任一起始與目的節點間都可輕易找到 數條不相交的路徑．在網路快速改變架構的情形下，多條路徑的利用對資 料封包傳輸的效率有很大的影響．本論文的目的在於分析利用連線指定維 護網路連接性的效率．另外也討論計算多條不相交路徑的演算法．利用這 些不相交的路徑，我們採用多封包傳送以改進系統效率和可靠性． Advanced communication satellites with store-and-forward packet switching capabilities have been proposed for constructing space-based computer networks. Satellites at the geosynchronous orbits are easier to manage, but incur long propagation delays. Low Earth Orbit(LEO) satellites are an alternative to reduce this delay which is critical for many delay sensitive applications. Because of the low altitude of LEO satellites, each satellite node is no longer geostationary and the network topology changes dynamically. The distance of communication links varies in time. In addition, links are often blocked by the earth. Therefore the network topology must be maintained by frequent link reconfigurations. This is an unique link assignment problem for LEO satellite networks. If each satellite is equipped with several communication links and the network is large, multiple disjoint communication paths exist between each pair of source and destination nodes. Routing data packets using multiple paths is of particular importance for networks with rapidly changing topology. In our thesis we analyze the effectiveness of link assignment algorithms for maintaining good network connectivity. Given instances of network connection, algorithms for computing multiple disjoint paths are studied. The computed multiple communication paths are used to demonstrate a proposed multiple packets multiple paths routing algorithm for improving system performance and reliability.