Caching Video Contents in IPTV Systems with Hierarchical Architecture

In this paper we consider IPTV systems with an hierarchical architecture. The lowest elements of the architecture are set-top boxes (STBs) at the user homes; a STB is connected to a central office (CO) which is in charge of delivering the video content to the end user. Since COs have limited storage capabilities, they may need to retrieve a particular video content that is requested by a user but temporary not stored in the local memory. Thus, COs exchange video contents with similar COs in a peer-to-peer fashion. At a higher hierarchical level, video source offices (VSOs) offer the video contents that cannot be retrieved at the CO level. Video content caching strategies at the COs and VSOs influence the system performance in terms of traffic exchanged between the network nodes. In this paper we propose two simple strategies that aim at reducing both the intra- and inter-level traffic. The strategies are studied by means of an analytical model that is validated against simulation results. Our results show that the hierarchical architecture allow good system performance even with limited overall storage capacity. The proposed strategies, in particular, can be helpful in improving system performance.