ibility that requires that the MSs can cooperate about resources of common interest. A similar situation exist between management systems of different interworking operator networks. Two interworking management systems may both be TMN systems, which facilitates interworking. Often they are not (e.g., one may be a TMN system, the 5.4 The Management System other an SNMP system), which creates a more difficult interworking situation because they specify MOs differently, for example. Interworking between management systems can comprise anything from inter- working between element managers to interworking between service managers. If two MSs must interwork around a shared resource (e.g., a route, a charging record) that is represented by MOs, they must also have a common understanding of that resource. This common understanding can be specified as something called virtual MO (vMO) in AMLn. The set of all vMOs that are agreed upon between two MSs will act as a contract between them that defines which information in one MS is available to the other, and which resources in one MS may be managed by the other. In their communication, the two MSs will refer operations and reports concern- ing virtual MOs. Locally, however, they must translate such information to opera- tions and reports of MOs defined for their own traffic system (or part of a common traffic system). To support this paradigm, a TMN manager that interworks with another MS must include a translation function, as indicated in the model in Fig. 5.13 (here exemplified as interworking between network managers). Note that interworking between management systems requires attention to authentication and other security issues, such as leaves-dropping and unauthorized intrusions. Interworking NM Local operator Local Locale-virtual MO translator SM,BM for MS2 interworking operator Fig. 5.13 Interworking between management systems can be specified by virtual MOs (vMO) A scenario is included in this model (only one way is shown here, but it works both ways, of course): 1