臺灣博碩士論文加值系統

新一代位於傳輸層之串流控制傳輸協定STCP(Streaming Control Transmission Protocol, SCTP)在網路傳輸上沿用與TCP(Transmission Control Protocol, TCP)相同的擁塞控制(congestion control)機制，每當傳送端偵測到封包遺失，皆視為網路擁塞發生，傳送端會大幅度減少擁塞視窗(congestion window)大小來避免擁塞的情況。但是在有線/無線網路環境下，封包的遺失並非全然肇因於網路擁塞，例如無線網路發生無線訊號錯誤，此時如果仍大幅度降低擁塞視窗，將無法妥善運用現有的有線/無線網路之頻寬。

為了改善SCTP擁塞控制的效能，特別是在因無線傳輸訊號錯誤致使網路具有一定封包遺失率的情況下，本論文提出一個適應性的擁塞控制方法以增進SCTP的效能。此一利用接收端頻寬估計之串流控制傳輸協定稱為RSCTP(Receiver Bandwidth Estimation SCTP, RSCTP)，其中包含SCTP封包遺失的判別方法是透過接收端回饋的可利用頻寬(available bandwidth estimation)與傳輸流量作比較，決定封包遺失的原因再對擁塞視窗做適當的調整。在多重定址(Multihoming)的模式下，RSCT因為加入了估計封包遺失率的功能，所以能夠在封包遺失嚴重時進行傳輸路徑的主動的切換。

本論文是以NS2網路模擬工具對所提出之RSCTP進行驗證，模擬網路擁塞與無線訊號錯誤的情形，模擬之結果相較於SCTP證明RSCTP可以對擁塞視窗作出適當調整，能有效提升SCTP擁塞控制在無線網路的效能。

Streaming control transmission protocol (SCTP) is one kind of new generation transport layer protocol, is a little modification form TCP. Like TCP, the congestion control mechanism of current SCTP which rely on packet loss as an indicator of network congestion. When congestion been detected the sender will reduce congestion window size to half to avoid congestion. In wire/wireless network environment, the packet losses are not all ways because of congestion. If SCTP reduces the congestion window inappropriately in an error prone wireless network, it may not use the network resource efficiently. For the purpose to improve the performance of SCTP congestion control, especially in an error prone wireless network, we propose a new enhancement SCTP called RSCTP (Receiver Bandwidth Estimation SCTP) based on receiver-side available bandwidth estimation. RSCTP relies on bandwidth estimation to discriminate wireless loss from congestion loss over error prone wireless link, it also reduces congestion window and slow start threshold appropriately. In multihoming mode, using chunk loss rate estimation, RSCTP can switch path actively over the high loss rate environment. We use NS2 to simulate RSCTP and the simulation results reveal that our scheme improves performance efficiently over error prone wireless network in evidence.

中文摘要……………………………………………………………i
英文摘要……………………………………………………………ii
誌　　謝……………………………………………………………iii
目　　錄……………………………………………………………iv
圖 目 錄……………………………………………………………vi
表 目 錄……………………………………………………………viii
第一章 簡介………………………………………………………1
　　 1.1 研究動機………………………………………………2
1.2 論文架構………………………………………………3
第二章 背景知識與相關研究……………………………………4
2.1　串流控制傳輸協定簡介…………………………………4
2.1.1資料塊限定………………………………………5
2.1.2多重定址…………………………………………7
2.1.3多資料流…………………………………………7
2.1.4回應機制…………………………………………9
2.1.5擁塞控制…………………………………………9
2.1.6亂序傳輸…………………………………………12
2.1.7部分可靠傳輸……………………………………12
2.2　二項式擁塞控制演算法…………………………………12
2.2.1收斂於公平………………………………………14
2.3 傳輸層通訊協定的無線網路效能改進…………………16
2.3.1窺探法……………………………………………16
2.3.2預測流量控制與其強化版本……………………17
2.3.3無線網路傳輸層進階控制………………………18
2.3.4連結層錯誤警告串流控制傳輸協定……………20
第三章 接收端頻寬估計串流控制傳輸協定……………………21
3.1 頻寬估計…………………………………………………22
3.1.1主要路徑的頻寬估計……………………………22
3.1.2備用路徑的頻寬估計……………………………23
3.2 SCTP封包遺失率估計…………………………………25
3.3 修改可達性要求/回應資料塊…………………………26
3.4 RSCTP的擁塞控制………………………………………27
3.4.1傳送端的運作……………………………………28
3.4.2接收端的運作……………………………………31
3.5 收斂於平衡……………………………………………32
第四章 模擬實驗結果…………………………………………34
4.1 模擬實驗環境設定……………………………………34
4.2 RSCTP的參數設定………………………………………36
4.2.1實驗一：降低擁塞視窗函式的參數β……………………36
4.2.2實驗二：主要路徑的可達性要求傳送間隔……38
4.2.3實驗三：備用路徑的可達性要求傳送間隔……40
4.3 實驗四：無線訊號錯誤情況的效能表現………………41
4.4 實驗五：頻寬競爭公平性………………………………44
4.5 實驗六：TCP友好………………………………………45
第五章 結論與未來展望…………………………………………48
參考文獻……………………………………………………………50

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