Abstract
在各種網路服務中，數位視訊預料會是主要的交通量成分，並且將影響未來多媒體網路之服務品質。數位視訊交通通常佔用相當大的網路頻寬。為了維持一定的影像品質，固定位元率視訊傳輸模式將需要一直佔用高峰值的頻寬。如此一來便難免減低了網路頻寬的效率。反之，可變位元率視訊傳輸模式可在維持固定的影像品質下節省了可觀的頻寬，但缺點是其交通量的波動很大。當考慮可變位元率之視訊交通量在一個高速網路上進行傳輸及統計多工時，對於像是資料細胞遺失及延遲之類的問題必須仔細加以評量。在處理網路效能的問題之前，首先要完成可變位元率之視訊源的統計特性描述與模型建立。對於一個傳送可變位元率之視訊交通的網路而言，某些效能評估值會被傳統的隨機模型低估，這是由於它們缺乏對於可變位元率視訊源之長程相關性的描述。本論文是針對兩個具有充分長程相關性的可變位元率視訊交通源模型作進一步的研究。根據對一個實際的可變位元率視訊源樣本之自我相似性的深入觀察，以便用來修正模型的參數。並在電腦模擬的輔助之下，驗證了這兩個模型的長程相關性，且觀察到它們對於一個虛擬的非同步傳輸模式網路多工器佇列的影響。結果顯示修正後的模型更能正確地描述一個多媒體網路的佇列狀態變化情形。之後，一個利用在現有文獻上常用的流量近似法會應用在其中一個模型上，以便能理解虛擬佇列的末端分布趨勢。In considering variable bit rate (VBR) video traffictransmission through and statistical multiplexing on a highspeed network, problems such as cell loss and delay must bewell evaluated. Before handling network performance issues, anaccurate statistical characterization and modeling of VBR videosource should be done at first. Some performance measures of anetwork carrying VBR video source traffic are under-estimatedby traditional stochastic models due to their lack of long-range dependence to characterize VBR video sources. This thesisis a further study of two VBR video source models withsufficient long-range dependence proposed for MPEG coded videosources. Parameters of these models are modified and fittedaccording to a much closer inspection of the self-similarity ofa practical sample VBR video source sequence. With theassistance of simulation, the long-range dependence of thesetwo models has been verified, and their effect to thehypothetic queue in an ATM multiplexer is also observed. Ourresults also show that these modified models characterize thequeueing behavior of a multimedia network more adequately.Afterward a diffusion approximation is applied to one of theproposed model to realize the tail distribution of thehypothetic queue with some well developed techniques in theliterature.