he QoS and QoE (for services used by humans). 9.6 KPIs and Measurement Methods for Fixed and Mobile Services Example: End-to-End Delay Calculation in IP-Based Networks When a flow portion does not contain a satellite hop, its computed Internet Protocol packet transfer delay (IPTD) is (according to ITU-T Y.1541): IPTD (microseconds) < where Rkm km represents the route length assumption computed above, (Rkm x 5) is an allowance for "distance" within the network portion, while NA, ND, Nc, and N1 represent the number of IP access gateways, distribution nodes, core nodes, and internetwork gateway nodes respectively, and finally DA, DD, Dc, and D1 represent the delay of IP access gateway, distribution node, core node, and internetwork gateway nodes respectively (typically, nodes and gateways are IP routers). 9.6.1 Audit of QoS and Publishing the Measurements The QoS audit is targeted at verification of QoS experienced by customers in order to compare results against the obligations which are specified in licenses (e.g. for mobile operators) or in the SLA. There are different methods for audit of telecom operators; however, they are dependent on the types of access network (fixed or mobile) and ser- vices provided to end-users. For example, the audit in mobile networks may include a drive test performed on a periodic basis (e.g. weekly, monthly, quarterly), consumer surveys, and measurement data which are submitted monthly or quarterly by telecom operators which are also service providers (e.g. they provide voice, IPTV, and business services over managed IP network as well as IAS). For example, targeted consumer sur- veys can highlight certain weak elements in respect of QoS and will provide valuable feedback to operators. Such data will also allow customers to compare their QoS expe- rience with other users. The main goal of publishing the measurements is to help customers to compare QoS from different telecom operators SO they can make informed choices. NRAs typically are required to publish information on performance