d in three versions (IGMPv1, IGMPv2, and IGMPv3) by the IETF [2]. In the case of IPv6 networks, multicast listener discovery (MLD) is used, which has two versions (MLDv1 and MLDv2). Each of the routers engaged in multicast delivery of IPTV traffic joins a multicast group by using a multicast type of IP address assigned to the network interface (that belongs to that router) which joins the given multicast group. Although there are different standardized multicast routing protocols, the most widespread and typically used for delivery of IPTV traffic is PIM-SM (protocol independent multicast - sparse mode) [7]. However, in the last leg of the IPTV 6 Services in Fixed and Mobile Ultra-Broadband transmission (between network nodes and set-top boxes on the end-users' side), unicast can be used, while in the IPTV provider network, multicast is used. For QoS in the transport network, multi-protocol label switching (MPLS) and the DiffServ approach (Figure 6.4), as well as Ethernet QoS mechanisms (e.g. IEEE 802.1p), are used and can be mapped to MPLS and DiffServ QoS traffic types (and vice versa). 6.3 QoE for VolP and IPTV QoE is directly related to humans and how they judge QoS by using their senses, such as ears for voice services (i.e. telephony) and audio (accompanying video) and eyes (for watching video content). QoE cannot be related to machines, such as machine-to-machine (M2M) type of communications, while QoS can be associated to all types of services, including human-to-machine (e.g. client-server communication over the Internet, such as Web browsing, or real-time services such as IPTV or video streaming), human-to-human (e.g. telephony), and M2M services (e.g. various IoT services). Therefore, this section covers QoE for VoIP and IPTV. 6.3.1 QoE for VolP The QoE for voice is expressed with the mean opinion score (MOS), which is a sub- jective measurement done by human listeners placed in a "quiet room" (ITU-T P.800 [8], P.800.1 [9], P.800.2 [10]). Such an approach has existed since the PSTN era, SO it was not i