視訊隨選網路上的視訊訊務描述與管理

摘要

隨著網路上多媒體應用日益風行，隨選視訊因為在教育、商業、娛樂等方面皆非常便利，因此是種非常重要的應用。由於網路內容儲存與及遞送已逐漸發展為分散式的拓樸架構並設置在近端的都會/接取網路內，視訊資料在網路上傳輸的瓶頸也因此而移到近端的視訊伺服器中心對外連接的交換器或路由器上，於是近端網路設備的頻寬管理十分重要。
然而，因為視訊訊務對延遲以及封包遺失皆非常敏感，而且其資料流具有變動位元率的特性，又具有高變動的資料叢集現象，造成欲在網路上傳送視訊且要有良好的品質是件深具挑戰性的事。許多文獻提出各種訊務描述的方法以提供近端網路設備作為頻寬保留的依據，可是這些方法並未考慮目前網路頻寬常受制於接取網路的可用峰值頻寬有其上限的實際狀況。
在本篇論文中，我們針對非即時的隨選視訊服務提出一種新的視訊訊務描述模型，稱之為可容忍延遲的多漏斗式視訊訊務描述法。此方法以現有的確定性訊務模型為基礎，但不再採用最壞打算分析，並且將I、P、B畫面對於延遲容忍度不同的特性結合進來，以增進頻寬使用率。更重要地，我們將網路頻寬常受制於接取網路的可用頻寬上限的實際狀況，在機制中做充分的考慮與討論。 實驗模擬結果顯示，即使在有峰值頻寬限制的情況下，可容忍延遲的多漏斗式視訊訊務描述法仍然能夠擁有低延遲上限以及高連結數量的良好表現，而且在訊務描述方面亦比其他訊務描述模型更為精準。

 

Video Traffic Modeling and Management over Video on Demand Networks

Abstract

With the popularity of multimedia applications over Internet, Video on Demand (VoD) is an important application because of its conveniences. For effective network content storage and delivery, Content Delivery Network (CDN) is always proposed such that video server farms are located at the metro networks.
Therefore, one of the major bottlenecks for transmitting video applications over Internet is at the border router of server farms. However, the border router always needs accurate traffic characteristics information provided by video sources for efficient bandwidth management.
Up to now, many literatures have proposed some accurate video traffic description methods. However, these methods never consider the realistic situation that the peak data rate of access networks may probably be limited.
In this thesis, we propose a new video traffic description scheme, Delay-Tolerant Multi-Leaky-Bucket (DTMLB). DTMLB is based on the deterministic traffic concept but does not use the worst-case model for analysis. DTMLB also introduces the consideration of different delay tolerance characteristics among I-frames, P-frames, and B-frames to improve the bandwidth utilization.
Moreover, in our simulations, we also consider the realistic situation that the peak data rate is often limited by the available bandwidth bound of access networks. Simulation results show that when the peak data rate limitation is introduced, DTMLB can always provide lower transmission delay and higher bandwidth utilization than the other description methods. The description accuracy of DTMLB is also better than the other description methods in our simulations.