greement (SQA) and QoS parameters. parameters as well as customer QoS parameters. Finally, that results in the definition of the QoS agreement. The QoS parameters for the SLA purposes can be divided into the following groups: Direct QoS parameters. These refer to a concrete service element and can be deter- mined by direct objective measurements. Indirect QoS parameters. These are defined as a function of one or more direct param- eters. One of the most important indirect QoS parameters is service availability (SA). For example, QoS parameter service availability can be calculated by using the following simple equation (SA refers to service availability, while UA refers to service unavailability): SA [%]=100%-UA[%] (9.1) Further, UA can be calculated by measurement of the outage intervals and their aver- aging over the total measurement time, given as follows: UA [%] = ( outage interval/active time) X 100% (9.2) In this concrete example, given with Eqs. (9.1) and (9.2), the indirect QoS parameter is expressed through a direct QoS parameter such as average outage time (i.e. UA). 9.4.2 SLA and QoS Regulation Definition of QoS parameters in SLA contracts is required for promotion of the desired QoS level, but such agreements are not always effective because the desired QoS targets may not be clearly defined. For example, IAS with bitrates up to 100 Mbit/s does not clearly define whether the user can expect bitrates of 1 or 11 Mbit/s or any number of Mbit/s up to stated maximum bitrate, and whether such provision will be continuous over time. To be effective, a given SLA should include the following: 9.5 Specifying Parameters, Levels, and Measurement Methods The minimum QoS level offered to the customer specified by selected number of QoS parameters which are important to end-users (i.e. KPIs), not the average level to be achieved for all customers or the values (of the KPIs) that are provided only at shorter time intervals. The compensation payment for situations when the minimum level is not achieved. The sum shoul