l. Later the TOM model was revised by TMF to have three main sections: SIP (strategy, infrastructure, and product), OFAB (opera- tions, fulfillment, assurance, and billing), and enterprise management. This revised model is called eTOM. The functions of the NMS mainly fall under the resource management layer of eTOM that spreads across SIP and OFAB. Though the NMS data can be used for planning phases in SIP, its functions can be directly mapped to real-time network configuring and maintenance in OFAB. So this chapter will mainly be about the network management functions from the categories of resource management in OFAB of the eTOM model. The following categories are used to discuss resource management functions: Resource provisioning Resource data collection and processing Resource trouble management Fundamentals of EMS, NMS and OSS/BSS Resource performance management "Resource management and operation" support and readiness A set of resources are required to develop a service. The term Resource as used by TMF could be any type of hardware, software, or workforce used to develop the service and includes within its scope a network or an element in the network. Hence resource management functions of TMF maps to the functions performed by NMS. It should be understood that the NMS functions in this chapter are generic and would be available in most network management solutions. There are also network management functions that are suitable specifically for a particular kind of network and high level capabilities that are implemented to satisfy specific requirements, both of which does not fall in the generic category. An example of a management function specific to a particular type of network is HSS (home subscriber server) subscriber provisioning. This operation involves creating, editing, and deleting customer/subscriber related records on the HSS. Since the HSS is an element found only in an IP-based network, this provision- ing functionality can be seen only in IP-based networks like IMS (IP multimedia subsystem)