標題: 適用於網路多媒體之可調式誤碼校正機制設計
Adaptive Forward Error Correction for Internet Multimedia
作者: 曾勁源
Chin-Yuan Tseng
黃育綸
Yu-Lun Huang
電控工程研究所
關鍵字: 誤碼校正;多媒體;網路多媒體;AFEC;FEC;Forward Error Correction;Adaptive Forward Error Correction;Internet multimedia
公開日期: 2006
摘要: 可調式誤碼校正(Adaptive Forward Error Correction, 簡稱AFEC)是一種利用動態評估網路狀態調整冗餘封包數量,以達到提升接收端播放品質的機制。一般而言,AFEC常用在有即時性需求的網路服務中,特別是在多媒體服務方面的應用。因為網路服務的即時性的要求,所以當封包遺失時,將無法透過一般的重傳機制重新取得遺失的封包。因此,在AFEC中,不採用重傳機制和服務品質(Quality of Service, 簡稱QoS)的方式確保服務品質,而是改用動態評估及預測網路擁塞狀況,並以複製封包的方法調整冗餘封包的數量,讓接收端能即時取得遺失的封包以提升接收品質。然而,AFEC在網路環境評估與預測的準確性上常有誤差,使得接收端並無法有效率地利用冗餘封包來回復遺失的資料。換句話說,一旦因評估錯誤而造成注入過多的冗餘封包,不僅無法有效率的提升接收品質,反而會造成更嚴重網路擁塞情形。因此本論文提出了一套數學模型,目的在找出冗餘封包數量和接收品質的最佳平衡點。為此,我們設計了可套用到AFEC中的可調式回饋控制方法,提出了三種機制,能動態地依據網路現狀調整冗餘封包數量,以達到提升接收品質,避免造成網路擁塞的目的。除此之外,由於注入冗餘封包的緣故,單位時間內所能傳送的有效資料量也隨之減少,因此,本論文中也特別分析了冗餘封包與接收品質之間的關係,期望提供服務商注入冗餘封包,提升接收品質時的參考依據。
By injecting redundant packets, adaptive forward error correction (AFEC) mechanisms recover the lost packets at the receiver side and thus improve the receiving qualities of real-time applications over unreliable packet networks. In this paper, we propose a simple mathematical equation of packet loss rate, receiving quality and transmission overhead to find the optimal redundancy solution for real-time applications. In addition, three adaptive control schemes are presented based on the proposed equation: static, dynamic and advanced AFEC schemes. In these proposed schemes, the data block size, redundancy overhead and qualities can be adjusted based on the estimated loss rate and network status. Upon applying these schemes, the receiving qualities of real-time applications can be guaranteed by recovering the lost packets with the redundant ones. Compared with non-AFEC mechanisms, the simulation results also show that the proposed schemes effectively improve the receiving qualities with good performance and packet redundancy.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT009412542
http://hdl.handle.net/11536/80673
Appears in Collections:Thesis


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