zero billed usage scenarios. Adding/reducing the charge based on special plans selected by the customer. In rating, first the value of the attributes that are used for rating are identified from the formatted records forwarded by the mediation system (see Figure 20.16). Some of the attributes that effect rating are: Connection date and time: There could be special rates imposed on specific dates. For example, the service provider might option to give a promotional discount to all subscribers on Thanksgiving Day. The discount could also be associated to time (like 6 AM-6 PM) on the specific date. Time of day (TOD): Service usage has peak hours and off peak hours in a day. For example the number of users using the Internet would be more during office hours. To make effective utilization of resources, service pro- viders offer a low rate for service usage during off peak hours. It is quite Fundamentals of EMS, NMS and OSS/BSS Billing and settlement system Rating engine Mediation system Network infrastructure Figure 20.16 Message flow with rating engine. common to see some content providers specifying a download limit during peak hours while giving unlimited limits during off peak hours, another common scenario is reduced call rate for calls made between 10 PM and 6 AM. Day of week (DOW): The same scenario of peak usage during office hours has an implication on special rates on specific days in a week. The usage of some services like Internet will be less on holidays compared to regular work- ing days. Service providers account for these usage patterns by preparing rate plans to suit user needs. Duration of usage: Rating can be based on duration of usage. The total time is a direct indicator of usage interval. When a flat rate is applied for a predefined interval of time, charge to customer would be a simple multiple of rate against the number of intervals in the duration of usage. It can also happen that the rate plan follows a set of rating increments. That is, rates keep on incrementing every 30 or 60 seconds. Thi