路徑狀態偵測之傳輸控制協定

Abstract

當今許多通訊產品對於多媒體資料的需求越來越高，也同時擁有多種網路介面方便使用者隨時隨地存取網路上的影音資料。本論文研製一套通訊協定，可方便擁有多個網路傳輸介面之產品使用。上層的應用程式以及底層的實體層都不需要做出修改，本通訊協定可以主動偵測資料傳輸路徑的狀態，來決定該如何動態轉移資料傳遞路徑，提升資料傳輸的可靠度與流通量。 在這篇論文中，RSA TCP 著重在路徑選擇的控制。因為TCP本身擁有流量控制的功能，所以路徑上如果發生錯誤或者壅塞，將會嚴重的影響TCP傳輸的效能。RSA TCP的目標就是判斷出現有的路徑是否出現錯誤情況，並且自動將原有的TCP資料流導引到另外的路徑上。 RSA TCP 能夠讓錯誤路徑上的資料封包轉移到其他正常的路徑上，如果要求上層的應用程式來達成這樣的效果，那麼每一個有使用網路功能或者跟網路有關連的應用程式都得修改，加上產品的平台種類繁多，作業系統除了種類多、版本也多，如果要應用程式達成這樣效果，將會是一筆非常可觀的花費。如果要求底層的網路層來做到路徑偵測，網路層本身只有IP相關的資訊，除了IP以外，網路層沒有其他任何的資訊可以判讀路徑的狀態，所以網路層是不可能達成這樣的效果。 RSA TCP 本身跟上層的應用程式是互相獨立的，跟底層的網路層或者實體層也互不干涉，也就是說，使用RSA TCP 來達成路徑偵測並轉移，是最方便也是最符合經濟效益的一種方法。我們也在NS2的模擬器上跟原有的方法比較效能。實驗顯示，與傳統TCP相比，RSA TCP可以達到大於26%的流通量。

There are more and more communication devices or portable devices equipped with multiple interfaces for users to request much higher multimedia data than before. Users could access multimedia data anywhere and anytime. The protocol studied in this thesis can be adapted by the devices with multiple interfaces to access the internet without requiring the modifications of the applications in the upper layer. There is also no need for lower physical layer to do any modifications. The protocol can detect the state of the routing path automatically to determine how to transmit data through the new path dynamically so as to improve the reliability and throughput. RSA TCP emphasizes on the path switching control for TCP packets. TCP protocols feature flow control, its performance may be affected by the congestion or error along the path. RSA TCP focuses on how to determine whether the paths encounter a problem or not. After the decision made is to switch routing path, the routing information will be updated to re-direct the data stream to the new next hop. TCP packets can escape from the congestion path automatically. If users request applications to do the same job, every network associated applications need to be modified. And there are various platforms and operation systems. The modification requested on application will cost a lot. It is infeasible for users to request the change in network layer, because network layer only contains IP information and is no routing information maintained in this layer, therefore it is unable know what happened and what to do. RSA TCP is independent of upper application layer and network layer, and it helps system keep the best performance for data communications with low cost. We perform the experiment for our method on NS-2 simulator and compare the performance with the original designed method. It shows that, comparing with traditional TCP, more than 26% throughput improvement can be achieved with RSA TCP.