level QoS measurement tests on international level ISP - Internet service provider IXP - Internet exchange point Figure 7.11 Measurements of Internet QoS at national and international levels. 7.8.3 Discussion About the Sampling Methodology Regardless of the evaluation scenarios and the types of tools used in the measurements (e.g. hardware-based or software-based), the crucial aspect is having confidence in the results. For the purposes of a high level of confidence in the QoS measurements, the number of probes to be used in testing should be large enough to cover all parts of the network and collected data from measurement is sufficient from a statistical point of view. Also, the data collection should be designed in a manner that reflects the QoS as it is being perceived by the end-user. Further, the measurements with the sampling methodology should reflect the market share regarding the number of selected access lines for each speed package, with aim the sampling methodology to be confident [23]. As usual, there are differences between QoS measurements in fixed and mobile access networks. For mobile networks, for example, probe stations should be positioned at different locations around the country and be proportional with the installed capacity in a given region (e.g. more probes are required in urban areas than in suburban or rural areas). For broadband QoS measurements in fixed access networks (e.g. DSL, cable, or fiber access), the selection of access points for QoS measurements can be challenging because one endpoint of the measurement must be located at users' premises (QoS is always considered end-to-end). In such cases (for fixed broadband), cooperation between NRAs, consumers, and ISPs is required, with the aim of attracting sufficient number of end-users volunteers which will want to par- ticipate in the QoS measurement campaign by allowing installation of either hardware or software probes at their end. Even in the case when there are enough probes, the broadband QoS measurements are not continuous 