應用於點對點視訊串流錯誤回復之封包遺失模型

A Packet Loss Model for Error-resilient P2P Video Streaming

羅啓文(Chi-Wen Lo) ； 林嘉文(Chia-Wen Lin) ； 陳永昌(Yung-Chang Chen)

《電腦與通訊》 153期 (2013/10) Pp. 121-128

摘要

本論文提出一應用於網狀點對點（Peer-to-peer, P2P）視訊串流的封包遺失機率模型。在P2P網路中視訊封包會因為傳輸錯誤和網路擁塞而被節點間的鏈結捨棄。此外父節點不預期的離開也會造成此子節點大量的封包遺失。利用封包前向錯誤更正碼（forward error correction code, FEC）可以有機會回復遺失的封包。使用FEC會編碼出資料封包與額外的冗餘封包，這會增加頻寬使用量。在實際的點對點網路中，上傳頻寬是有限的，無法冗餘封包給任意數目的要求節點。於是我們需要一個封包遺失機率模型來評估上傳頻寬分配給各個要求節點所帶來的傳輸品質改善程度。此模型考慮了節點間傳輸的封包遺失、節點加入離開行為、FEC資料保護機制來描述視訊傳輸在網狀網路中的封包遺失行為。利用此精準的封包遺失機率模型，我們提出一個子節點選擇法來選擇對封包遺失有貢獻的子節點傳送冗餘封包，以降低封包遺失擴散。子節點的封包遺失貢獻度是由封包遺　失機率模型來估算，當封包遺失機率模型越準確，就越可以正確地分配頻寬來傳送冗餘封包，達成頻寬的有效利用。實驗結果證明本文提出的模型可以準確的估測網狀網路環境下的封包遺失率，所提出的節點選擇法可以有效地分配節點上傳頻寬來消除封包遺失。

關鍵字

點對點視訊串流 ； 網狀結構 ； 封包遺失 ； 前向錯誤更正

並列摘要

This paper proposes a model to estimate the packet loss probability in a mesh-based P2P streaming system. The video packets transmitted in P2P networks are dropped by the links between peers due to transmission error and network congestion. In addition, the unexpected parent-peer departure will cause the burst packet loss in their child-peers. The lost packets may be recovered by packet level forward error correction (FEC) code which encodes data packets and extra redundant packets. However, FEC also consumes more bandwidth to transmit redundant packets. In a real-world P2P network, the uplink bandwidth of peers cannot afford the enormous amounts of redundant packets. Hence a packet loss estimation model is required to decide the adequate amounts of redundant packets for each peer. The proposed model considers link packet loss, peer dynamics, and FEC protection scheme to characterize the packet loss behavior of video transmission over a mesh network. Based on the proposed model, we also propose a child-peer selection mechanism which can effectively mitigate packet loss propagation by selecting the child-peers to transmit redundant packets. The simulation results show that the proposed packet loss model can accurately estimate the packet loss in the different mesh-based network environments. Besides, the proposed peer selection method efficiently mitigates packet loss.

並列關鍵字

P2P Video Streaming ； Mesh-based Structure ； Packet Loss ； Forward Error Correction ； FEC