This artifact specifies how billing/charging is to be performed. Commonly used billing/charging schemes are schemes relying on the data volume provided (i.e. volume-based), the number of requests for, or connections to, a service (i.e. I/O based) or the time period the service can be used (i.e. time-based). While in some cases flat billing/charging schemes may be an adequate solution (as they are simple to set up and use), it is also possible to combine the above-listed schemes into a hybrid scheme.