twork element and its element management solution. The functions in a network management system involve actions that can be per- formed on all the network elements. To have a common set of functions applicable EMS Functions Network management system Adaptation layer EMS-a EMS-b EMS-c NE-b1 NE-b2 Figure 4.2 Normalization at adaptation layer. to all the elements there must be consistency in the data handled at NMS. The adaptation layer performs the conversion required to a common format for han- dling the data at NMS. Another method to solve this problem is to have well-defined standards of interaction. The set of queries that the NMS will send to an EMS or the underly- ing network element is to be defined. TeleManagement Forum (TMF) is working toward this initiative with its standards on multitechnology network management (MTNM). 4.6 Service Assurance When a customer subscribes to a service, a service level agreement (SLA) is made with the service provider. Service assurance involves ensuring that the service pro- vider is delivering the guaranteed level of service to the customer. It is mainly comprised of: Service quality management Trouble or problem management Quality of service (QoS) is a key component in service assurance covered in service quality management that ensures speed and reliability of service. The QoS requirements are used to derive the network element and its resource requirements for entities such as call processing, data communication, and storage. The QoS parameters relevant to requirements in service level agreement are identified, moni- tored, and controlled. The QoS parameters may be oriented toward: performance (example: data rate) format (example: delay with different codec for media transmission) cost (example: different billing packages like first 100 calls free) user (example: quality of user experience QoE) Fundamentals of EMS, NMS and OSS/BSS There is also a service agreement on fixing trouble in service and restoration of service within a specified time. It is here that trouble or 