Determination of the cause of degradation of the quality of a service based on the evolution of a set of services

The invention relates to a exchange for group used for determining a service can end of the voltage of quality, especially a service management system, for determining possibly is at least a service drop the edge of the set of network element, the is characterised of comprising for determining the service device of quality, and for acting according to the following parameter by the fixing the: deviceThe other service the made; For providing of the service network element.