改善無線串流服務 : 
訊框丟棄與封包遺失原因之區分演算法

近年來串流服務已成為網路的主要應用之一，加上無線網路快速普及，在無線網路上提供串流服務已成為一項重要的議題。然而由於無線傳輸媒介的特性，如較低的頻寬和較高的位元錯誤率，使得在無線網路上提供串流服務比在有線網路上，更具有挑戰性。當我們經由一資源有限的網路傳輸串流影片時，有時候因為頻寬的不足，導致部分的資訊遺失是不可避免的。為了提高網路頻寬的使用率，我們必須先傳送對影片品質有較大影響的訊框(frame)。因此我們提出一以相似度為基礎的訊框丟棄演算法(Similarity-based Frame Discard)，依相似度決定各影片訊框的重要性。目前串流連線普遍採用TCP Friendly Rate Control (TFRC)為其壅塞控制機制以達到和傳統TCP連線公平地競爭網路資源的目的。如同TCP，TFRC在遇到封包遺失時，會認為網路已經進入壅塞狀態並調降傳送速度，以免網路的負荷量持續增加。但在無線網路上，由於較高的位元錯誤率，封包遺失可能是由無線傳輸媒介的不穩定所造成。因此，盲目地遇到封包遺失就調降傳送速度將會造成頻寬使用率的低落。為了解決此一問題，我們提出了以趨勢和遺失密度為基礎的遺失原因區分演算法，利用封包傳送時間的改變趨勢和封包遺失的密集程度，判斷封包遺失的原因是否為網路壅塞，抑或為無線媒介所造成。

關鍵字

無線；網路；串流

並列摘要

Streaming is more challenging in a wireless network than in a wired network, because wireless networks have their own characteristics such as low bandwidth and high bit error rate. We propose two schemes to address these issues. When we deliver a video stream across a bandwidth-constrained network, loss of frames may be unavoidable. To maximize the perceived quality-of-service at the client side, it is desirable to find a server transmission schedule that can transmit important frames first and utilize the network resources efficiently. To address this issue, we develop Similarity-based Frame Discard (SimFD). Unlike previous works, we select frames into transmission schedule by taking both frame similarity and inter-frame dependency into account. The frames that are less similar with their previous frame will get higher priority. TCP Friendly Rate Control (TFRC) is a widely accepted rate control method for streaming in the Internet. It assumes that packet losses are primarily due to congestion, and reduces sending rate in the present of packet losses. But this is not applicable to wireless networks in which the bulk of packet losses are due to wireless channel error and not relative to congestion. To help TFRC differentiate the losses caused by wireless channel error and avoid reducing sending rate blindly, we develop an end-to-end approach, Trend and Loss Density based Loss Differentiation Algorithm (TD). Our approach is based on the observation that congestion losses often occur after the ROTT peak and always appear in burst.

並列關鍵字

wireless ； streaming ； frame ； network

參考文獻

[2] Zhang, Z. L. , Nelakuditi, S. ,Aggrawal, R. ,Tsang, R. P.: Efficient Selective Frame Discard Algorithms for Stored Video Delivery Across Resource Constrained Networks. Proceedings of IEEE INFOCOM 98

[4] Hari Balakrishnan , Srinivasan Seshan , Randy H. Katz, Improving reliable transport and handoff performance in cellular wireless networks, Wireless Networks, v.1 n.4, p.469-481, 1995

[5] A. Bakre, I-TCP: indirect TCP for mobile hosts, Proceedings of the 15th International Conference on Distributed Computing Systems (ICDCS'95), p.136, May 30-June 02, 1995

[7] Saad Biaz , Nitin H. Vaidya, “Discriminating Congestion Losses from Wireless Losses using Inter-Arrival Times at the Receiver”, Proceedings of the 1999 IEEE Symposium on Application - Specific Systems and Software Engineering and Technology, p.10, March 24-27, 1999

[8] Y. Tobe , Y. Tamura , A. Molano , S. Ghosh , H. Tokuda, “Achieving moderate fairness for UDP flows by path-status classification”, Proceedings of the 25th Annual IEEE Conference on Local Computer Networks, p.252, November 08-10, 2000

國際替代計量

改善無線串流服務 : 訊框丟棄與封包遺失原因之區分演算法

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