 to be aware of telecommunications networks and services as col- lections of cooperating systems. The architecture is concerned with orchestrating the management of individual systems SO as to have a coordinated effect upon the network. Introduction of TMNs gives PTOs the possibility to achieve a range of management objectives including the ability to: Minimize management reaction times to network events. Minimize load caused by management traffic where the telecommunication network is used to carry it. Allow for geographic dispersion of control over aspects of the network operation. Provide isolation mechanisms to minimize security risks. Provide isolation mechanisms to locate and contain network faults. Improve service assistance and interaction with customers. 21.9 TMN FUNCTIONAL ARCHITECTURE The TMN functional architecture is structured from the following functional elements: Function blocks Management application functions (MAFs) TMN management function sets and TMN management functions Reference points TMN management functionality to be implemented can then be described in terms of these fundamental elements. 21.9.1 Function Blocks Figure 21.14 illustrates the different types of TMN function blocks and indicates that only the functions that are directly involved in management are part of a TMN. Some of the function blocks are partly in and partly out of a TMN; these TMN function blocks also perform functions outside of the TMN functional boundaries as discussed below. The TMN function block is the smallest deployable unit of TMN management func- tionality. If the TMN function block contains a management application function, it may only contain one management application function. Operations Systems Function (OSF) Block. The OSF processes information related to the telecommunications management for the purpose of monitoring/coordinating and/or controlling telecommunication functions including management functions (i.e., the TMN itself). Network Element Function (NEF) Block. The NEF is a functional block whi