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 ...