IP services). IPTV functional architecture consists of different functional entities, which include end-user functions, application functions, SCFs, CDFs, network functions, manage- ment functions, and content provider functions. Such IPTV functional architecture can be used for different delivery mechanisms, including multicast delivery and unicast delivery of IP packets carrying the IPTV content. Regarding the design of IPTV transfer over IP networks, the most efficient way for linear IPTV channels (linear TV refers to TV content which is transferred to all users that have chosen the given TV channel at the same time) is the use of multicast routing. In fact, multicast routing is intended for use in real-time services where many recipients listen and/or watch the same content. Why is multicast routing for IPTV better for the telecom operator's network than uni- cast? To answer this question, let's assume that the operator provides 100 IPTV channels to its customers. Each channel with SDTV requires 3 Mbit/s per channel and 6 Mbit/s per HDTV channel. Let's have 100 000 active IPTV users (watching one IPTV channel per user at the same time) in a given region being served by the given IPTV provider (of course, this is an example; in practice it is dependent upon the size of the country and the telecom operator). If only unicast is used in the network, then on a network link between nodes A and B which (in this example) carries all traffic to all 100 000 users, capacity of 100 000 x 3 Mbit/s = 300 Gbit/s will be needed in the case of SDTV channels, or 100 000 x ( 6 Mbit/s = 600 Gbit/s capacity in the case of HDTV channels. Although such capacities in the transport networks in the 2010s and the 2020s can be provided, multicast saves the capacity needed in the network, SO IPTV can be provided at a lower price or with a higher profit margin (since less capacity is used in the network), or the remaining capacity can be used for other IP traffic (e.g. Internet traffic, IP managed traf- fic), which can bring additional re