 endpoints of the established communication session), which may be oper- ated by different network providers (i.e. telecom operators). As shown in Figure 1.6, Real-time Internet Core network Access IP transport of the telecom (includes all network network networks to the operator remote end) Streaming Network Network Network Network performance performance performance performance Internet data Remote equipment Total network performance Quality of service (QoS) Technical part of QoS Figure 1.6 Network performance, QoS, and QoE. 1 Introduction NP is the detailed technical part of the offered QoS. Also, NP contributes to QoS as experienced by the user [12]. The functions of a service depend on the performance of the network elements and the performance of the user's terminal equipment. QoS is always end-to-end, which can be user-to-user or user-to-content (one may also add here QoS for machine-to-machine communications, which may be directly not related to a human end-user). Hence, QoS is always an end-to-end characteristic, where it depends on the contributions from different components (Figure 1.6), including the end-user, its equipment (smartphone, computer, etc.), access network (fixed or mobile), IP transport network, core network, and the rest of the path end-to-end (e.g. through the Internet). QoE has a broader scope because it is impacted by QoS as well as by user expectations and the context. Meanwhile, QoS has broader scope than NP. 1.4 ITU's QoS Framework ITU has developed a QoS framework to suit different networks and services, initially defined in ITU-T G.1000 [12] and then in ITU-T 802 [13]. The framework is continu- ously evolving. To provide QoS support for a given service, QoS criteria and then QoS parameters based on the criteria need to be defined. Such definitions of QoS criteria were initially given in ITU-T recommendation G.1000, which provides the general QoS framework (by the ITU). Before defining QoS parameters, QoS criteria relevant to the user are required. The main goal is to establish a 