hile on the other side the NP is determined by the performances of network elements one by one, or by the performance of the network as a whole. So, the NP has an influence on the QoS, and it represents a part of it. However, the QoS is not influenced only by the NP but also by non-network performance parameters. Simply said, QoS consists of network performance and non-network performance, as shown in Figure 1.5. The NP concept is applied for purely technical purposes, i.e. assessment and analy- sis of technical functions. NP is the ability of a network portion or the whole network to provide the QoS functions related to communications between the users. Network performance is determined by the performance of network elements one-by-one. The Table 1.1 Mean opinion score for the quality of experience. Mean opinion Quality score (MOS) classification Excellent 1.3 Introduction to QoS, QoE, and Network Performance Quality of service (QoS) Network performance Non-network performance Figure 1.5 Network performance (NP) and quality of service (QoS). performance of the network as a whole (end-to-end) is determined by the combina- tion of the performance of all single elements along with their interconnections on the communication path between the end-user devices. NP is specified in terms of objec- tive performance parameters, which can be measured, and then the performance value is assigned quantitatively [10]. 1.3.4 QoS, QoE, and NP Relations All three terms - QoS, QoE, and NP - are related one to another. QoE is different from QoS and NP as it has a subjective nature by definition, and because it depends on the end-user's perception. Clearly QoE is impacted by QoS and NP. For example, if NP is lower, it will result in lower quality experienced by the end-user. Further, NP applies to various aspects of the network provider's functioning, includ- ing planning, development, operations, and maintenance of network elements and the whole network. Also, there can be several interconnected networks (along the path between the