Analysis and placement of storage capacity in large distributed video servers

Abstract

In this paper, we study how to distribute storage capacity along a hierarchical system with cache-servers located at each node. This system is intended to deliver stored video streams in a video-on-demand way, ensuring that, once started, a transmission will be completed without any delay or quality loss. We use off-line smoothing for videos, dividing them into CBR video parts. Also, our request rates are distributed following a 24 h audience curve. In this system, when a request is received, the server reserves the required bandwidth at the required time slots, trying to serve the video as soon as possible. We perform a detailed analysis by means of simulations of the start-up time delay for some storage distributions. It shows that an adequate storage distribution can increase performance about 25% with respect to a uniform distribution and about 47% with respect to one in which all the storage is attached to the gateway routers that connect the final users. We also analyze bandwidth usage, comparing the behavior of these storage distributions. Finally, we present a method which allows dynamic and transparent video reallocations when their popularity changes.