TCP (Transmission Control Protocol) 是當今最重要也是最被廣為使用的傳輸協定，其可正常運作於純有線的網路環境之下。但由於最近幾年之內無線網路的迅速發展，TCP被迫由純有線的環境轉到有線無線共存的複合式網路下運作。於無線網路中，由於高錯誤率(BER)的原因，封包隨機的遺失使得TCP經常非必要的調降其傳輸視窗大小，這樣的一個行為造成TCP於無線環境下效能低落。而這一個問題已經被研究多年也有多種的方法提出來解決此一問題，JTCP是眾多方法中表現最好的一個。但不幸的是，就算這些方法能夠正確判斷封包遺失的原因，在判斷正確後TCP的行為卻可能造成傳輸超時(timeout)。為了解決這樣的問題，我們修正了JTCP的判斷遺失機制並提出了平緩傳輸機制(smooth transmission mechanism)，如此的做法可以增加對封包遺失判斷的正確性以及避免大量傳送資料所造成的傳輸超時。另外我們也針對802.16中傳輸模組改變時所造成的影響提出對應方案。由實驗結果顯示，我們所提的強化JTCP傳輸機制(EJTCP)在複合網路中傳輸表現高於其他方法。 TCP is the most important and widely used transport protocol at present, and it can work well over the purely wired network. But in virtue of expanding of wireless network in the recent years, TCP must transfer its working environment form purely wired link to wired-cum-wireless network. As a result of high bit error rate (BER) in wireless, TCP halves down its congestion window unnecessarily caused by random packet loss event regularly, and the performance is really bad in wireless network. The problem about differentiating loss has been investigated for a long time and many schemes were proposed to solve this problem. JTCP has better performance among those schemes. Unfortunately, even if those schemes can judge correctly, some events may occur to make TCP timeout. To solve this problem, we amend JTCP scheme and propose a smooth transmission scheme to increase the correctness of loss distinction and avoid burst transmission. We also propose a scheme to deal with modulation changing in 802.16. The experimental results show that our scheme, enhanced JTCP (EJTCP), unrolls better performance than other algorisms over wired-cum-wireless network.
