ere is required precision level of +3% for the same con- fidence level of 95% there will be required 1067 samples from the measurement of the same parameter under the same conditions (Table 7.8). 7.7.2 Basic Network Model for Measurements In an ideal scenario QoS measurements would be made between the same endpoints for each type of customer's traffic. These endpoints are the customer's terminal (TE - terminal endpoint), customer equipment such as edge router (CE - customer edge), or provider edge router (PE - provider equipment) [22]. Generally, the IP network is partitioned in segments, which include access network and core networks (ingress and egress segments) and transit networks. Hence, a given telecom operator (i.e. provider) can be access provider and/or transit network provider. The point of interconnection (POI) of access network and regional network (e.g. core Table 7.8 Measurement sample sizes and confidence intervals. Confidence level Degree of variability Precision level Required number of samples 7.7 QoS and QoE Assessment Methodologies Transit segment Regional Regional network A network B Demarcation Demarcation POP A POP B Transit networks PE-PE Access Access network A network B Demarcation points Site-to-site Site A Site B TE-TE CE - Customer edge PE - Provider edge POP - Point of presence TE - Terminal endpoint Figure 7.9 Network models for QoS measurements. network of the telecom operator) is referred to as demarcation POP. The providers offer services between different endpoints which include the following cases: Edge-edge services. In this case the demarcation points (DPs) are PEs (provider edge routers). Site-site services. In this case the service extends to the customer edge point (managed CEs). TE-TE services. In this case the services extend to the customers' terminals. The types of offered services by providers in fact define the positioning of the measure- ment points, based on the network model for QoS measurements shown in Figure 7.9. In this model network is partitioned on network 