Scalable end-to-end quality of service monitoring and diagnosis in software defined networks

Methods and a system are provided for detecting a Quality of Service degradation in a network flow. A method includes configuring, by a monitoring element, at least two network elements on a path of a network flow to report statistical information pertaining to the network flow as time series data. The method further includes collecting, by the monitoring element, the time series data from the network elements. The method also includes computing, by the monitoring element, a similarity of the time series data. The method additionally includes indicating, by the monitoring element, the Quality of Service degradation when the similarity is below a specified similarity threshold.