The present invention relates to a method and system for inspecting a session in a packet data network, wherein a set-up message is selectively routed to a predetermined server node (4001, 4002) and processed there. A media resource function (3021, 3022) is controlled based on the processing so as to bind incoming and outgoing data streams in order to relay the session via the media resource function. Thereby, a mechanism for providing charging, filtering and logging services for sessions, such as peer-to-peer chat sessions, is provided without requiring any new network entity or modification of existing network specifications.