分散式系統容錯之時間同步化策略及其在Web環境之應用「時間同步化」一直是分散式系統中極具重要性的課題，不僅是某些容錯應用方面需要有時間同步化來配合，如訊息的全域排序等等，即使在非容錯方面的研究上，也經常使用時間同步的假設，來確保其作業的正確。所以時間同步化是分散式系統中相當重要的一環。然而時間同步化的問題有多方面的考慮因素。在分散式系統中，不僅是各個節點上有各自不同的時間，它們的時間也可能各自以不同的速度在進行著；還有在時間同步化上常常會使用到其它的參考時間，通常需要使用網路環境來取得，因此網路的延遲也是時間同步化考慮的一個因素；另外錯誤的參考時間，也會嚴重影響時間同步化的正確性等等。這些都是我們在研究分散式系統時間同步化的問題上，不可忽略的重要因素。本論文提出一個分散式系統上的時間同步化策略，我們使用「滑動視窗演算法」來確保時間協議的正確性與可靠性，並討論目前使用於分散式系統容錯之時間同步化的策略種類與評估比較。另外，Web環境將成為未來分散式系統主要之應用平臺，我們亦探討將時間同步化策略應用於Web環境時所遭遇的困難與限制。為提供Web環境時間同步化，我們使用CORBA技術來解決Web環境上的限制，並在Web環境發展出一套具容錯能力之時間同步化系統－Web Ticker系統。

Time synchronization is the topic of great importance in distributed systems. Many fault-tolerance related applications need time synchronization in their systems, for example, the message total ordering. Even for many non-fault-tolerance related applications, they also need to assume the system clocks in their systems are synchronized. So time synchronization is considered as one of the important parts of distributed systems. The problem of time synchronization has various aspects. In distributed systems, not only the different nodes have different times, they may also be running at different speeds. To synchronize the system clocks on various computers often require the reference times in different nodes. This job is completed through the communication network. So it needs to consider of the delay of communication network. Another fact to think is the possibility of faulty reference times. The faulty reference times will affect the precision of time synchronization. All the above problems are very important on solving time synchronization in distributed systems. In this thesis, we propose a time synchronization strategy on distributed systems, we use the "Sliding Window Algorithm" to ensure the correctness and reliability of time consensus. On the other hand, World Wide Web environment will become the major platform for distributed systems in the near future. In this thesis, we discuss the difficulties and problems to provide time synchronization on webs.In order to provide the capability of time synchronization on webs,we use the CORBA technology to solve the limitations on web, and develop a fault-tolerant time synchronization system called "Web Ticker".