eed between the service provider and the cus- tomer by using an SLA. Such an approach allows the user to have an SLA only with the primary service provider (that is the telecom operator which provides the access net- work to the user, either to the public Internet or to managed IP networks) as the sole provider responsible for the QoS received. Such an approach can continue between the primary service provider (in regard to the given user) and its sub-providers, though this is not directly related to the SLA signed with the end-user. The QoS agreements with sub-providers (e.g. transit network providers) refer more to the aggregate traffic at the interconnection points between the given provider and its transit providers. 9.4.1 QoS Agreement The part of the SLA which defines the QoS is referred to as the QoS agreement. Its main goal is to define the agreed QoS with the end-user (when signing the agreement) and to obtain the end-user's satisfaction. For the purposes of the SLA and its corresponding QoS agreement, the definition of QoS parameters (e.g. minimum, average, and maxi- mum supported bitrates are different definitions of the bitrate as a QoS parameter) is essential [5]. In all cases the QoS parameters should be defined in a clear way, which means with "simple" language that can be understood by the ordinary end-user while more technical details in the QoS agreement can be used for QoS agreements with other network and service providers. The definition of QoS parameters is required for development of the SLA and corre- sponding QoS agreement (Figure 9.3). Overall service level requirements influence the choice of QoS parameters, including service dependent and service independent QoS 9 QoS Regulatory Framework Service level requirements Service independent Customer QoS Service dependent QoS parameters parameters QoS parameters Inter-operator service Inter-operator service independent QoS parameters dependent QoS parameters Service quality agreement (SQA) QoS - Quality of service Figure 9.3 Service quality a