. For example, if the operator, the NRA, independent agency for QoS measurements, or end-users want to perform QoS measurements on the operator's network, they use a client application installed at the end-user's side (or hardware/software probes installed in defined locations for measurement purposes) and the server endpoint (for active measurements) is typically connected to the IXP either nationally (for assessment of QoS in the targeted telecom operator's network) or internationally (for assessment of end-to-end QoS in the more realistic scenario where traffic traverses multiple autonomous networks on the path between the two endpoints, the client and the server). 9.5.1 Defining QoS Parameters For the purpose of defining QoS parameters, there is typically a need to involve telecom operators in the process. To avoid possible stronger influence (by operators) in such a consultation process, the NRA needs to have strong leadership, taking into the account the various factors that may influence the choice (of QoS parameters). However, the Table 9.1 List of proposed parameters. Customer interface Network infrastructure Service functionality Complaint Broadband access coverage Call setup ratio (for voice) submission rate (fixed or mobile) Complaint Service supply time Call retention ratio (for voice) resolution time Customer service Fault report submission rate Listening voice quality (mean opinion call answer ratio score - MOS grading) Fault repair time Message transmission ratio (e.g. for SMS, Data transmission capacity (e.g. downlink and uplink for IAS, typically specified in Mbit/s) Packet delay (in ms) Packet error ratio (probability or %) 9.5 Specifying Parameters, Levels, and Measurement Methods measurements should be possible for operators, and there should be the possibility to use independent agencies/entities for audit of the measurement results obtained from different operators. But the most important thing is to retain the aspects of real customer experience for the given services. A possible list of Q