A very important question in IP networks, on which depends the development and implementation of the new demanding applications and services is the Quality of Service. The Quality of Service requirements can change through the variable user demands, or variable communication circumstances. Therefore, it is probably that the applications and services will be performed with variable level of quality. The variable level of quality require introduction of new mechanisms, which will enable such class of service. This dissertation incorporates the requirements for the Quality of Service from the application and the service point of view, user equipment requirements and the cost of the service. The ways for serving the services with different level of guarantees are defined. From the users point of view, a procedure for choosing, changing and adapting the proper Quality of Service is determined. The QoS architecture model for the applications and the services with variable services requirements is proposed. The QoS parameters, which are specific for this kind of service and the service classes, are defined. The experimental verification of the proposed model is performed in laboratory simulated IP network environment, with few simple service classes. The property of the proposed model for choosing and negotiating the quality of service, by the variable quality requirements is ascertained, as the efficient network resource management.