Un sistema de vídeo bajo demanda a gran escala tolerante a fallos de red.

Abstract

A Large Video-on-Demand system (LVoD) offers a large number of geographically distributed users access to video files. The most complete Video-on-Demand (VoD) service allows users to request their chosen video and reproduce it almost instantaneously, as well as the possibility of using interactive controls (pause, fast/ slow forward and rewind etc.) just as if you were watching a video using a VHS or DVD. This service is known as True Video-on-Demand (T-VoD) and implies a design and development of high complexity. Most VoD systems were designed for dedicated networks or networks which enable resource usage. However, the architecture of these systems is not applied to LVoD environments, mainly due to new scalability requirements, the cost of the system and fault tolerance. When the network environment changes from a Local Area Network (LAN) to Wide Area Network (WAN), the probability of faults increases, the bandwidth decreases and the quality and classification of services is replaced by a "best effort" service model. This thesis proposes a distributed LVoD system architecture which permits a T-VoD service with unicast communications on a network without quality of service (QoS) such as Internet. The new architecture, Video-on-Demand with Network Fault Recovery (VoD-NFR) aims to prevent network faults and server down, and guarantee delivery of multimedia content to clients without lowering its quality and without interruptions during viewing. To achieve these objectives, the model designed includes three key components: - A traffic scheduler with the ability to: 1) adapt the output traffic to the network congestion in a TCP-Friendly manner, 2) generate communication state information of the server with each client, and 3) maximise resources saving to resist a high workload. - A logical channel scheduler with the ability to: 1) use VBR videos, 2) continuously adapt to the bandwidth available of the communications, 3) not degrade the quality of the video in order to adapt to a lower bandwidth than that required by the video, and 4) fairly distribute the video to clients, prioritising those with a greater media need. - A module to guarantee quality of service with the ability to: 1) detect problems in the communication between servers and clients using two mechanisms which work together in detecting faults resulting from deterioration of communications, and 2) to continue offering a service without interruptions by service migration. The VoD-NFR system has been implemented in a real environment and a simulation; the system was evaluated more extensively and at a lower cost using the simulation. The results obtained show the system's ability to fulfil its objectives and they support continued investigation of the system.

Date of Award	17 Jul 2008
Original language	Spanish
Supervisor	Remo Suppi Boldrito (Director)