Consistent and flexible policy and charging control is one key factor for effective access control and efficient resource management in IP-based multimedia communication networks. One approach to deal with this challenge is to put more decision logic into the so-called mediation layer which is residing between the operators’ core network and the charging system. This article describes our research study to extend the mediation layer with more capabilities for online charging control. The presented prototype implements and extends parts of the 3GPP Policy and Charging Control Architecture using the open source JAIN SLEE framework Mobicents.