ng time. Enormous CDR flow: One of the biggest challenges in designing media- tion systems is to make it scalable enough to handle enormous CDR flows. There are a large number of call or usage records that are pumped to the mediation systems at any given point of time. The mediation systems should OSS/BSS Functions have a mechanism to collect all the records and process them in the shortest possible time. Data correlation: The correlation between records to send consolidation information is also a challenging activity considering the wide variety of ser- vices being offered and the network infrastructure deployed by the service providers in current telecom industry. There are several billing systems that take feed from the mediation system as depicted in the figure on mediation data usage. Data from the mediation systems is used to compute the network usage charges, interconnect charges, roaming charges, and other value added service charges. The data is also achieved in a stor- age system for future reference or for processing by business support solutions like planning, which try to identify usage statistics based on aggregated information in historical records. Next we will discuss the rating engine whose role it is to apply pricing rules to a given transaction, and 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 