Abstract: The present invention relates to a method for performance analysis of data networks where data is collected as measurement samples from the individual network elements at in-synchronous sampling intervals and stored in a Performance Database. Said database is maintained by a Performance Local Agent, which stores collected data in the database, retrieves data from the database on request from a client, processes the data and provides clients with a view of the data. According to the invention, measurement samples are normalised by interpolation so as to appear as samples sampled at exactly the same sampling times.