A behavior investigating device of a system investigating arrangement in a communication network continuously obtains statistical network usage data of users, analyzes the statistical network usage data with regard to the pattern of behavior of the users, prioritizes the users based on the analysis and informs a traffic prioritizing function about the priority of at least one of the users. The traffic prioritizing function, which may be provided in the traffic prioritizing node, determines that there is network congestion, identifies a communication session of a user in the communication network, obtains a priority of the user from a behavior investigating device and determine whether the user is to be allowed to use the communication network based on the priority and the congestion determination.