en the origin and destination as in tra- ditional billing methods. This is because IP distance will not be a key factor and it will be parameters like quality of service and security level that deter- mines the tariff to be imposed on the service subscribed by the customer. Interconnect billing: Services can span across multiple service providers. For example, a simple phone call between two people can involve two ser- vice providers, when each of them is serviced by a different service provider. Outgoing call charges are imposed by one service provider at the call origi- nating end and incoming call charges are imposed by another service pro- vider at the call terminating end. This setup connecting the network from different service providers/operators requires some kind of billing mecha- nism to monitor the actual amount of data (sent and received). It is known as interconnect. Some of the billing models are: Volume-based billing: Here the bill is calculated based on the volume of data (total size). An internet service provider charging the customer based on the volume of data upload and download is an example of using volume-based billing. Duration-based billing: In this billing, time is the determining factor. An Internet service provider charging the customer based on duration of sessions the user is connected to the internet is an example of using duration-based billing. Content-based billing: This model is most common in IP billing. In this bill- ing, the type of content offered to the customer is the determining factor. It can be applied on services like video broadcast, multimedia services, gaming, and music download. Charging process can be: Off-line charging: In off-line charging the service rendered cannot be influ- enced by the charging information in real-time. Online charging: In online charging the service rendered can be influenced by the charging information in real-time. Online charging is becoming increasingly important with convergent services where a third-party con- tent provider will be pa