適用於不穩定無線網路下具高輸出效率之UDP可靠檔案傳輸機制

High Throughput UDP Based Reliable File Delivery Mechanisms For Unstable Wireless Networks

葉信延(Xin-Yan Yeh)

指導教授 ： 孫宏民

國立清華大學/電機資訊學院/資訊系統與應用研究所/碩士(2012年)

摘要

今日，無線網路技術越來越成為我們每天生活的一部分，不同於IEEE 802.3的有線網路，無線網路的訊號非常容易受到環境限制的影響。本篇論文中，我們考慮了在不穩定無線網路下的檔案串流。為了提高檔案串流傳輸的效率，結合了＂正向錯誤更正技術 (FEC)＂及＂回饋確認頻道＂的方法被研究人員使用著，而實作在＂應用層的正向錯誤更正技術 (AL-FEC) ＂，便是將一個物件 (檔案)，切成許多區塊，並使用加解密的編碼演算法，修復遺失封包區段；接著是針對每個區塊的＂回饋確認頻道＂能夠確保傳送端與接收端知道正在傳送的區塊是否已經足夠，我們以＂封包來回時間 (RTT)＂與＂Iperf＂流量來決定傳送端與接收端間連線的狀態，並且我們使用許多WiFi基地台連接成的＂無線分散系統 (WDS)＂來建立不同RTT與頻寬大小的環境，且由於是在不穩定的連線狀態下，斷線處理機制也是一個重要的議題。在這篇論文中，我們提出了4種R-FLUTE架構，以不同的ACK頻道 (TCP或UDP) 及傳送方式 (單一檔案或多檔案) ，實驗中更證明了，在不穩定環境下，R-FLUTE擁有超過FTP 10% 到 80%的傳送效率。

關鍵字

用戶數據報協議 ； 檔案串流

並列摘要

In recent years, wireless technologies become more and more important in our daily life. Dierent from IEEE 802.3 wired network, wireless signal is more sensitive with the variation of environment, resulting violent round trip time (RTT) and packet loss rate variation. In this paper, we consider a video streaming over environment with unstable connection quality. In order to improve the throughput and reliability in video streaming, we consider streaming content le delivery and combine Forward Error Correction (FEC) with feedback mechanism. With Application-Layer
FEC (AL-FEC), we depart a object (e.g., a le) into many blocks and use encoding/decoding algorithm to repair the lost part of the blocks. Then a feedback mechanism
for each block makes the sender knows if the receiver possess enough symbols to decode. We investigate RTT and Iperf throughput between sender and receiver as our basis to determine the quality of connection. To simulate various RTT and bandwidth environments, we connect WiFi APs with Wireless Distribution System (WDS). Because of unstable connection quality, the disconnection handling mechanisms
is also a very important issue. In this paper, we propose four Reliable-FLUTE (R-FLUTE) schemes with various ACK channel (TCP or UDP) and sending flow (single file or multiple files). The experiment result shows that in comparison with FTP, R-FLUTE protocol have 10% to 80% throughput gain in unstable environment cases.

並列關鍵字

UDP ； Video streaming

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