segments, where each segment is being monitored independently according to the three service cases (edge-edge, site-site, and TE-TE). Typically, telecom operators are interconnected with peering over some transit networks. A given service provider can act as an access provider for some traffic and as a transit provider for some traffic, or can have both roles for a given type of traffic. 7.7.3 Quality Assessment Methodologies The quality can be assessed with parameters that can be measured on network segments or end-to-end and compared with target reference values (for those QoS parameters), 7 Broadband QoS Parameters, KPIs, and Measurements or they can be assessed on the basis of the users' experience from service usage (e.g. it refers to services used by human users). Hence, there are two main methodologies for QoS/QoE assessment: Subjective assessment method. In this case the quality of audio and video media that are consumed by human users is evaluated in subjective terms. However, "real" subjective quality assessment, where human subjects evaluate the quality of various services under different testing conditions, can be time-consuming and expensive. Also, for such testing scenarios there are required professional audio-visual devices or soundproof chambers. Therefore objective quality assessment is preferred as a means for estimating subjective quality solely from performed objective quality measurements. As already discussed, MOS is used as a measurement grade (from 1 to 5) of the average subjective opinions on a given quality metric. One should note that non-utilization QoS parameters (Table 7.2) are subjectively assessed by using questionnaires (filled by end-users on voluntary basis) given to customers (after completion of certain non-utilization service) via Web form, email, SMS, or other digital (or paper) forms. Objective assessment method. In this case objective quality assessment is used to estimate subjective quality (i.e. QoE) by using solely objective quality measurements (i.e. QoS). In practice