A communications system in which event based charging is implemented and in which service flows between end user equipments and application servers are filtered for charging purposes by a traffic plane function (TPF). The TPF identifies a service flow between an end user equipment and an application server and implements event based charging by sending a message to an Event Owner for the service flow requesting notification of Events associated with the service flow. The Event Owner sends a message containing an Event Result to the TPF when an Event associated with the service flow occurs and the TPF correlates the Event Result with the service flow. This correlation may include the matching of the Event Result to the service flow which the TPF then notifies to a billing control function so that the billing control function can bill the end user appropriately based on the Events. This correlation may also include the matching of the Event Result to a data download detected by the TPF on the service flow so that the system operator can confirm that the service flows filtered by the TPF match the Events notified to the TPF by the Event Owner.