Packet-switched network technology is expected to form the integration layer for future multi-service networks. The trend to integrate voice and data traffic can already be observed in the Internet and is expected to carry on until the full integration of all media types is achieved. At the same time it becomes obvious that the business model employed for current Internet usage is probably not sustainable for the creation of an infrastructure suitable to support a diverse and ever-increasing range of application services. Currently, the Internet provides only a single class of best-effort service and prices are mainly built on flat-fee, access-based schemes. However, the large and increasing differentiation of demand for quality of transmission services creates the necessity to differentiate service provision and, consequently, charging for network communications. In this article, we survey relevant service models and motivate the need for appropriate charging mechanisms. We give an ov...