ied according to the structure of traffic-system models 5.4.2 The TMN Management System The OSF (the user of MOs) is not standardized. However, because of the functional complexity of the OSF itself, TMN (which was intended for public network opera- tors) deals to a great length with classifying all functional requirements on the OSF. Although the TMN classification may be overkill for other public networks (e.g., the Internet), its function classification approach is interesting as an exercise in managing functional complexity. TMN suggests a separation of the complete OSF in management functions that are relatively independent and have well understood relations to each other. The classification system has two dimensions: "functional levels" and "functional areas." The functional level classification is based on an assumed or possible network structure of logical nodes in a management system (MS). The ESMs of those nodes are called "managers". The structure suggest that each OSF functional level can be allocated to managers of its own. Four types of managers are suggested that deal with network element management (EM), network management (NM), service management (SM), and business management (BM) (see Fig. 5.12). In this model we make a distinction between mpCP and msCP, the latter being control points inside and between management systems (thus invisible to traffic systems). We have also indicated the possibility for different management systems to interwork (more about that later). 5.4 The Management System operator operator (part of OSF) (part of OSF) operator (part of OSF) operator (part of OSF) operator operator Fig. 5.12 The structure of OSF managers in a management system. BM=business manager; EM=element manager; NM=network manager; SM=service manager 1. Element manager (EM). TMN suggests that a manager connecting to network elements (NEs) will deal with logging, backup and maintenance of implementa- tion elements (hardware and software) in the network elements it connects. In addition it can deal with th