The present invention relates to a system and a method for charging in a communication network and to a communication network charging server. The system comprises a client (1) associated with the network for providing services to subscribers associated with the network. The charging server (2) is adapted to handle subscriber account information, and the said client (1) is adapted to send a first charging request message for a service, to the charging server (2) before the service is provided, using an on-line charging protocol (3). The charging server (2) is also adapted to perform pre-reservation of an amount of resources from the subscriber's account, wherein the amount depends on a requested amount included in the message about the service, and to return an answer message including information indicating whether an amount of resources is pre-reserved from said subscriber account for enabling usage of the service to the client (1) using the on-line charging protocol (3).