網際網路中，TCP（Transmission Control Protocol）為傳輸層中最被廣泛應用的協定，它主要設計是在一個不可靠互相連接的有線網路上，提供可靠的點對點傳輸。隨著科技日新月異，無線網路環境快速的發展，由有線與無線建構起的網路架構也愈發成熟，異質性網路在未來中將扮演著極重要的角色，然而，根據之前的研究與我們的實驗，TCP的壅塞控制演算法卻沒有考慮到無線網路的特性。在無線連結比起有線而言是非常不可靠的，任何時間可能會遺失封包且遺失率較高，而現有的TCP實作都假設封包遺失或逾時是因為壅塞引起的，因而調降傳送的速率，此一做法主要是想降底網路的負載，進而緩和壅塞的狀況，但在無網環境中，封包不因壅塞遺失最適當的處理方法就是儘快重新傳送，將速度調慢只會讓它的效率變差。事實上，當封包遺失在有線網路上，傳送端應該要減速；而是遺失在無線網路上，則不應該降底傳送率。如果能讓傳送端分別出封包在何種網路類型中遺失的，必定能改善TCP在無線環境中效能不好的問題。在此篇論文中，我們提出了一個新的方法，利用封包遺失與延遲變異判斷網路連結是否壅塞（congestion），由實驗數據結果顥示，以延遲為基礎的壅塞判別技術在異質性網路中的確有較好的表現。 TCP, a widely used transport protocol performs well over the traditional network which is constructed by purely wired links. As wireless network is growing rapidly, the wired/wireless mixed inter-network, a heterogeneous environment will get wide deployment in the next generation ALL-IP wireless networks. TCP which detects the losses as congestion events could not suit the heterogeneous network in which the losses will be introduced by higher bit error rates or handoffs. There exist some unsolved challenges for applying TCP over wireless links. End-to-end congestion control and fairness issues are two significant factors. To satisfy these two criteria, we propose a jitter-based scheme to adapt sending rates by the packet losses and jitter ratios. The experiment results show that our jitter-based TCP (JTCP) conducts good performance over the heterogeneous network.
