t Management Systems (EMSs). These EMSs interface with a particular type of NE various device to conduct management functions. An EMS can communicate with the NE using a variety of protocols i.e., SNMP, CMIP, TL1 or Telnet. Since one single domain may consist of NEs from many different vendors and of various flavors, multiple EMSs will likely be used at the EML layer to manage the devices in the domain. A domain manager is responsible for management tasks within a domain, such as maintaining inventory and setting up logical connections. A domain manager uses the appropriate EMSs to configure and retrieve information from NEs. Whereas a domain manager manages intra- domain resources, the inter-domain manager is responsible for managing and controlling inter-domain or cross-domain resources. The inter-domain manager treats each domain as a "Node" much the same way a domain manager treats a NE. The inter-domain manager manages resources across the domains and then leaves the task of managing intra-domain resources to The Ultimate Guide to Building and Delivering OSS/BSS the respective domain managers. This coordination at a higher level in the hierarchy ensures alignment among the activities performed by the domain managers. This multi-domain management framework also allows multiple levels of hierarchy and multiple levels of inter-domain managers. For example, a NMS package A from a vendor may only manage IP and ATM domains but not the optical domains. In this framework, package A is an inter-domain manager that controls multiple domains, transparent to upper levels. Another package B may be called upon to manage the optical domain and hence we would need another inter-domain manager managing package A and package B. This multi-level hierarchy provides the flexibility to architect OSS/NMS systems to manage complex network configurations. The multiple domain (multi-domain) challenge is most evident in the areas of inventory management - the gathering, aggregating and synchronizing of physical and logical inventory f