utive. The customer can also call the support desk for clarification on billing related queries. The customer support desk will have access to specific (subset) billing information to service the queries. However, most support professionals ask sufficient authentication queries to ensure that private information is disclosed only to the intended owner of an account. Some support professionals also request permission from customer, if the support personal can access the account owners billing data and if required, modify it. The billing system will interact with the accounting modules in NMS to get the billing records. The billing records generated by the elements in the network are handled by the element managers and network management systems to provided relevant billing data to the billing system. There is an account database that the bill- ing system will query to get information on customer account balance, credit limit, billing rules to be applied as per SLA, tax to be added as per regulations, additional charges for usage of specific service, and SO on that are associated with generating a final bill to the customer. Two important modules in the billing OSS are the mediation system and the rating system. All service providers have a mediation system that consists of several subsystems to capture usage information from the network and service infrastruc- ture and distribute it to upstream BSS modules like billing, settlement, and mar- keting (see Figure 20.14). The subsystems collect billing records from the various network infrastructures supported by the service provider and provide feed to the central mediation system that aggregates the records, performs correlation between records, repairs records with errors, filters the records based on predefined rules, and maps the data to a target format required by the business support systems. Some of the popular formats handled by the mediation systems include CDR, IPDR, and SDR (see Figure 20.14). Mediation functions can be classified into usage data collection