| Summary: | SCTP (Steam Control Transmission Protocol)是由IETF[2]提出在傳輸層的新機制。SCTP像TCP一樣提供擁塞控制機制(congestion control mechanism)。此外，SCTP提供Multi-Homing和Multi-Streaming兩個TCP所缺乏的重要機制。然而，SCTP和TCP一樣無法分辨當快速重傳機制(Fast-Rtx)或是Timeout機制啟動時，packet-loss發生的真正原因，如瞬間的通道錯誤或因網路擁塞引起的封包拋棄。於此，SCTP會不正確地啟動擁塞控制機制來防止網路擁塞狀況的持續惡化。
本篇論文目的在於改善SCTP在無線網路所遭遇效能低落的問題。我們提出三種解決問題的機制，分別是SCTP-EnhancedProbing、SCTP-Duplicate 及SCTP-Changeover。SCTP-EnhancedProbing機制是一種點對點的方法，用以判斷packet-loss發生的真正原因。SCTP-Duplicate機制則藉由multi-homing機制來幫助提升SCTP-EnhancedProbing機制的效能。SCTP-Changeover機制則是一個必要的方法來補足SCTP-Duplicate機制所引發的問題，以提供良好的改善方案。最後，我們將利用網路模擬器NS-2 (Network Simulator ver. 2)來驗證並評估我們所提出三種方法的效能。
=== SCTP (Stream Control Transmission Protocol) is a new proposed mechanism by IETF [2] at the transport layer. SCTP has similar congestion control mechanism as that in TCP, and embeds multi-homing and multi-streaming mechanisms that are not offered by TCP. However, SCTP can’t identify exactly whether the cause of packet-loss is from transient channel error or congestion error as fast-transmission or timeout is triggered. SCTP will thus invoke congestion control mechanism incorrectly.
The objective of the thesis is to improve the performance of SCTP which suffers performance degradation in a wireless network. We propose SCTP-EnhancedProbing, SCTP-Duplicate and SCTP-Changeover three mechanisms for this end. SCTP-EnhancedProbing is an end-to-end mechanism used to identify the cause of packet-loss. SCTP-Duplicate employs the multi-homing feature to enhance SCTP-EnhancedProbing performance. SCTP-Changeover is a necessary complement to SCTP-Duplicate mechanism. Moreover, the proposed SCTP-Changeover is an effective solution to the changeover problem in SCTP.
At last, we verify and evaluate the performances of the three proposed mechanisms using Network Simulator 2 (NS-2), respectively.
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