前向錯誤更正系統在多媒體通訊的應用

Abstract

可靠的傳輸可以由自動重傳要求或前向錯誤更正來達成，對即時性的多 媒體應用而言，自動重傳要求並不適合，尤其是一對多的應用，如廣播系 統，自動重傳要求會使伺服器成為系統瓶頸，疲於應付個個客戶不同的重 傳要求。前向錯誤更正的好處是，不論是一對一或是一對多的傳輸，客戶 都可以自行在當地回復錯誤。本論文將簡介前向錯誤更正理論，並發展了 一套適合多媒體傳輸的前向錯誤更正系統，同時我們也發展了一套完整的 系統界面，將系統模組化，讓多媒體應用程式可以容易的和本系統結合， 由單機應用轉成網路多機互動的應用，而不需要知道網路傳輸的細節。本 論文最後成功的將MPEG的layer2壓縮和本系統結合，發展了一套即時的廣 播系統，驗證了系統的可行性。 Reliable transmission can be achieved by both ARQ (Automatic Retransmission Request) and FEC (Forward Error Correction). For most real-time multimedia applications, especially for one-to- many applications like broadcasting systems, if ARQ is used, the server will be busy retransmitting lost packets because each client may have different patterns for lost packets. The advantageof FEC is that clients can recover lost packets without asking the server to retransmit. In this paper, we will introduce the scheme of forward error correction, and we will develop a FEC system for multimedia transmission. We also define a general interface such that application programs can be integrated with our system without knowing the details of our system by using the interface. At final, we will combine our system with the MPEG layer2 encoders/decoders to form a broadcasting system.