e able to determine network performance and measure it against SLAs and take action upon QoS degradation, such as providing billing credit or re-configuring network resources to meet SLA requirements. 3.3 Real-Time Usage Collection and Billing Billing for the circuit-switched services have traditionally been based on minutes of use. Even when service providers started offering packet-based services, they were still billing on a flat-rate basis. However, there is an increasing trend towards consumption-based billing for next-generation services. Service providers want to bill based on bandwidth reserved, QoS level desired, bytes transferred, applications downloaded and number of transactions. In addition, numerous pre-paid services are evolving that require service providers to rate usage in real-time. Mediation devices and usage collectors pull usage figures from network elements, servers, Web sites and portals and then aggregate and correlate that information to customers and services based on telephone number, IP address, Mobile Device Identifier, NAI, Cable Modem or MAC address. Numerous standards exist for capturing usage data i.e., CDR (call detail record) for minutes of use service, IPDR (IP detail record) for measuring IP packets transmitted/received and TDR (Transaction Data record) for measuring number of transactions performed by the user. 3.4 User-Interface Considerations The NGN OSS will have to provide robust, flexible and distributed user- interfaces for affective management of the network infrastructure and to also allow end-customers to self-manage their services. The OSS user-interface will have to support the following functions: - Web-based: Given the trends towards thin client architecture, the next- generation OSS must support access to OSS functions via a standard Web browser. This will support anytime, anyplace access and keep client software distribution costs low. The Ultimate Guide to Building and Delivering OSS/BSS Secure: Since multiple users will have access to the OSS functions, the 