5 - the best). QoS parameters can bas based on primary metrics that are determined by using direct measurement (e.g. circuit noise, echo path loss, or signaling release cause) or derived from a set of primary parameters (e.g. statistical operations on measured data, applying rating factor for obtaining estimates of customer opinion such as E-model rating, deci- sion thresholds). Particular QoS metrics can be defined to serve specific service types, such as: 7.2 Generic and Specific QoS Parameters QoS metrics for different types of services (e.g. voice, video, multimedia, various data). QoS metrics for one service type (e.g. video), but different types or subtypes of that service (e.g. for video service that can be VoD, IPTV, Web live streaming, video tele- phony, video conferencing). Different types or subtypes of the same service may have different requirements regarding the same QoS parameter (e.g. video conferencing is very sensitive to one-way delay, which is not the case with video streaming or VoD). QoS metrics for the same service type, but different commercial basis for the same service. For example, VoD or TV streaming over Internet access service (IAS) do not have QoS guarantees end-to-end (due to network neutrality principle for the Internet network) and occasionally may enter congestion periods (e.g. when such video traffic is multiplexed with a high volume of other Internet traffic). Meanwhile, paid IPTV service (and included VoD service) has guaranteed QoS end-to-end (e.g. guaranteed bandwidth). 7.2.1 Comparable Performance Indicators The QoS parameters and metrics must be important and understandable to the end-users, as well as comparable among different service and network providers. The agreed QoS values are also referred to comparable performance indicators [4]. Such QoS values (CPI examples are given in Table 7.1) enable customers to be aware of the actual variety of service quality to help them make informed decisions when choosing a provider (e.g. fixed or mobile telecom operator). 7.2.2 Sta