乙太被動光纖網路下改善服務品質的動態頻寬分配

Abstract

乙太被動光纖網路（EPON）被認為是下一代網路的明日之星，因為它能夠支援網路上日益增加的流量以及滿足人們對於網路各種寬頻服務的需求。這是因為它整合了既有的光纖基礎建設以及目前已發展成熟並且成本低廉的乙太設備。除此之外，另一個讓乙太被動光纖網路備受注目的原因是它的大頻寬解決了寬頻服務所帶來對頻寬需求激增的問題。在現今的多媒體網路傳輸環境下，傳輸服務品質（Quality of Service）就變的是很重要的議題。 在本篇論文中，我們提出了一個能適用於乙太被動光纖網路上改善服務品質的動態頻寬分配方法，我們針對及時性的服務(例如語音服務、視訊服務等)設計了以延遲以及封包被丟掉為考量的頻寬分配機制；另外，也針對非及時性的服務(例如一般資料服務)而設計了以避免它過度被犧牲作考量的排程機制。這是因為非即時性的服務時常會因為重要性比較低，在傳輸上往往會被犧牲而造成過大的延遲。我們為了減少這樣被過度犧牲的情況，在滿足即時性的服務下，改善非即時性服務的延遲情況。模擬的結果顯示我們所提出動態分配頻寬的方法確實能夠讓語音封包以及視訊服務的平均延遲和封包丟掉機率限制在一個可接受的範圍之內，並同時對於資料服務考量了對封包延遲與封包阻隔機率的支援。

To support the increasing traffic load and the growing demands of broadband multiple services in the network, Ethernet passive optical networks (EPONs) are the candidate of the next-generation access networks. The convergence of low-cost Ethernet equipment, lowcost fiber infrastructure, and the large bandwidth of the optical fiber link make the EPONs suitable for providing broadband services. Presently, in the multimedia environment, qualityof- service (QoS) becomes an important issue. In this thesis, we propose a QoS-promoted dynamic bandwidth allocation (Q-DBA) method to support transmitting delay-constrained voice and video packets, and starvationconsidered data packets. The goal of the Q-DBA method is to meet the delay criterion of voice service under the voice dropping probability is set to zero, the delay criterion and dropping probability of video probability, and to simultaneously maintain the delay of data packets. The data packets should not endure a long delay time although they do not have strict delay criterion. When the QoS requirement of real-time service can be satisfied, the performance of non-real-time service should be improved. Simulation results show that the proposed method can almost meet our goal. If combining call admission control (CAC), our goal can be totally achieved.