ile networks than in fixed networks. Mobility of the users. There is different mobility of different users, from nomadic mobile users (at home, office, or public place) to mobile users that are in transporta- tions vehicles (e.g. cars, buses, trains). The higher mobility is the lower is the bitrate over the same frequency spectrum resources due to usage of more robust modulation and coding schemes in such cases (which transfer less bits per symbol, hence result in lower bitrates). To combat radio interface and mobility of users (for higher QoS and QoE), one solu- tion is to use smaller cells in the mobile access network (that results in smaller attenua- tion of signals) which may support very high bitrates in the radio access part and provide higher QoE for mobile users (due to better QoS, that is, higher bitrates and smaller delays in smaller cells, especially for users with nomadic mobility). The QoS parameters in mobile networks can be classified in four layers, according to the ITU-T E.804 [14], as shown in Figure 7.7. The first layer is called "network avail- ability." It defines QoS from the viewpoint of the service provider. The second layer is "network access," which provides the basic requirements for all other service-related QoS parameters. The third layer in this model contains the other three QoS aspects from the service point of view: service access, service integrity, and service retainabil- ity. Finally, the fourth layer defines service-specific QoS aspects and parameters, which differ from one mobile service to another. Network Layer 1 availability Layer 2 Network accessibility Service Service Service Layer 3 accessibility integrity retainability Cloud Email transfer computing Mobile Video Mobile Layer 4 Mobile TV telephony telephony streaming Push over Internet of cellular Things Figure 7.7 QoS layering model for mobile services. 7.5 KPIs for Data Services and VPNs Regarding their implementation mobile services can be grouped into the following two main groups: Direct mobile services. These serv