Dimensioning of a Multi-rate Network Transporting Variable Bit Rate TV Channels

摘要

We consider a centralised (client-server) digital TV network with heterogeneous receiver devices of different resolutions, requiring a multi-rate transport system. There exist two main ways to store and transport (streamed) TV channels in such a system: either by providing different single-layer versions of a channel (simulcast transport mode) or by keeping one multi-layered version (encoded e.g. in SVC) with extractable substreams. We propose one approximate analytical and two simulation methods to estimate the capacity demand in such a network with variable bit rate channels and we consider two behaviour models. In some TV distribution networks, the video is delivered in constant bit rate. However, this implies that the video quality is varying. In order to provide better quality of service (QoS), a network operator must deliver the channels in non-constant bit rate aiming in this way at constant video quality. Our models take into account also the correlations between the different resolutions of a channel. Starting from real experimental data, we obtain the necessary input to our models and explore two realistic TV network scenarios - with bouquets of 50 and 300 channels, respectively. The results by the three approaches correspond well (relative error of 0.5% at most). In the case of 50 channels, SVC outperforms simulcast in terms of required bandwidth, while in the case of 300 channels, SVC is outperformed by simulcast. Therefore, we conclude that it depends on the system parameters which of both transport strategies will be more beneficial to save network resources.