route to the rated transaction to the appropriate billing or settlement system. Rating takes input from a predefined rules table and applies it on usage information provided by a mediation system. The charge computed by the rating engine is not just based on usage. The final charge has various rating com- ponents taken from modules like the order management, marketing management, and SLA management system. The main activities performed in rating are: Applying rating rules on the usage information for each of the customers. Applying any credits for outage. Applying discounts that are agreed upon as part of the customer order. Applying any promotions or offers on the charge. Applying credits for breach of terms in the SLA. Resolving unidentified and 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