Abstract: A method solves the problem of implementing flexile charging of subscribers so that no changes, or minor changes, need to do in charging systems. Hence, the problem is how the rating and charging of communication events can be separated. The method is provided for creating, due a detection of a communication event, a notification relationship between a network node and a rating engine, wherein the notification relationship obeys a charging control protocol. Then the rating engine forms a supplementary instruction on the basis of information obtained from the notification relationship. Finally, the rating engine sends the supplementary instruction to the online charging system that re-charges the communication event according to the supplementary instruction. The invention also comprises a rating engine in accordance with a single charging embodiment in which the rating engine alone controls the charging of the communication event.