gical layer of TMN. When mapping it with functional architecture the OSF of the network elements are associated with this layer. Fundamentals of EMS, NMS and OSS/BSS Currently, the operation support system (OSS) mostly used in association with service management applications is supposed to incorporate all management func- tions as in OSF of the TMN functional architecture. When we segregate manage- ment functionality into business, service, network, and element management, the business management application got associated with BSS, service management application with OSS, network management application with NMS, and element management applications with EMS. 3. Network management layer (NML): The responsibility of this layer is to manage the functions related to the interaction between multiple pieces of equipment. Some of the functions performed in this layer are: Creating a view of the network Correlation of network events Single-sign-on to elements in the network and the element managers Traffic management based of attributes and behavior of network elements Monitoring network utilization and performance A detailed discussed of network management is handled later in this book. 4. Service management layer (SML): This layer, as the name signifies, is con- cerned with managing services. Service is what is offered to the customer and hence this layer is the basic point of contact with customers. To realize any service there is an underlying network and SO the SML uses information presented by NML to manage contracted service to existing and potential customers. The SML also forms the point of interaction with service provid- ers and with other administrative domains. Some of the functions performed in this layer are: Service provisioning User account management Quality of service (QoS) management Inventory management Monitoring service performance A detailed discussion of service management functions is handled later in this book under OSS. 5. Business management layer (BML): This is the top most layer in the TMN 