culated. This record is stored in a database and aggregated over the billing cycle. At the end of a cycle (like a month for monthly billing of calls), the aggregated records are used by modules like an invoicing system to prepare an invoice for the customer. There can be different billing models that can be applied based on the SLA with the customer. It can be flat bill where a fixed amount is billed for usage of service, or a usage-based bill where the bill reflects the customer's utilization. Another example along the same lines is real-time billing where the debit from a prepaid account or amount to be paid for on a postpaid account can be viewed as soon as a service is used. Now let us see an E2E flow of how the modules discussed in this section (see Figure 19.3) interact to offer a service like telephony. Every activity starts with a business requirement. So first the customer contacts the sales desk and uses a Web interface to request the service. Once the credit check is performed and the customer can place an order, the required customer details and service information is feed to the order management system. The order management system creates a work order and sends the details to the provisioning system. The provisioning system sends What Is OSS and BSS? Customer Customer Sales and Order relationship Billing customer care management management Service/resource Inventory Service/network Trouble management and management provisioning management operations Figure 19.3 Mapping of the support system process. data to the inventory system for allocation of appropriate resource. If some manual setup is required before starting the automated provisioning, then a work request a trouble ticket is created. Using the workforce module, the request is assigned to a technician for resolution. Once the setup is ready, the provisioning module initiates provisioning of service and the network. Once provisioned, the service is activated and the billing module is triggered to collect and work on the billing records. 19.8 Con