rom multiple domains; service provisioning and activation - the assigning and activating end- to-end network and application resources across multiple domains; and fault management - the gathering of network fault events, correlating fault and determining the root cause, again across multiple domains. The key to cost-effective management of the network infrastructure of the future (which includes integrated and legacy domains) will be a successful development of a multi-domain architecture and development/deployment of systems in line with this architecture. 3.1.1 Inventory Management Inventory Management entails maintaining a constant view of the physical and logical resources in the entire network and keeping that data synchronized with the network. The inventory management function often also includes resources that are pending installation, such as spare parts, warehoused equipment, and faulty equipment. For the purpose of this discussion we will focus on the most important aspect - the assignable or provisionable network inventory. This inventory is a "shared" enterprise resource since multiple OSS/NMS processes such as provisioning and activation, fault management and performance management use this inventory. A network consists of multiple logical domains such as the DSL domain, ATM domain, optical domain and IP domain. While we call them logical Chapter 8 - Next-Generation OSS because they are all integrated at the network level, because each domain has its own unique characteristics. The concept of multi-domain inventory management calls for a hierarchical arrangement of network inventory. At the lowest level individual domain managers maintain an inventory of network resources - network elements, shelves, cards, links, channels and circuits within their respective domains. In our example of Figure 11, there are three logical instances of intra-domain databases for inventory. One level higher in the hierarchy, an inter-domain database inventories the domains themselves (represented as a node) and the int