rough M1 combined with M2. M4 deals with their public ATM switches and networks. M3 is the link between private and public networks, used for exchanging fault, perform- ance and configuration information. Finally, M5 supports interactions between any two public networks. The definition of these interfaces allows a complete manage- ment service, ranging from a global view of the network (M5 management inter- face) to the management of individual elements (M1 management interface). In some cases, several management interfaces use the same information from a management information base (MIB) tree.4 We now elaborate on the management interfaces but omit M5 as significant work remains to be done on this standard (also see Table 3.3). 4 See Chapter 4 on SNMP for a quick introduction to MIBs. OSS for Telecom Networks Table 3.3 Management interfaces. Management Description interface Interface between corporate NMS and user device Interface between corporate NMS and private ATM network Interface between NMS Interface between carrier NMS and public ATM network 3.3.1 M1/M2 Interfaces and the ILMI Implementation We explain the M1 and M2 interface by describing the Interim Local Management Interface (ILMI), which is an implementation of the M1/M2 interfaces. ILMI enables the exchange of status, configuration, accounting and control information between any two ATM devices - such as two ATM switches - across a user-to-network inter- face (UNI). For ILMI to function, every ATM switch or network terminator and every ATM network that deploys a public or private network UNI must be equipped with a UNI Management Entity (UME) which supports an ILMI MIB. Two adjacent (or peer) UMEs can communicate using the common attributes provided by the ILMI. By sending SNMP commands, a UME may obtain or modify (if the object is indeed modifiable) information contained in its ILMI MIB. The ILMI MIB is hierarchically organised (Table 3.4). It contains information concerning each group listed in Table 3.4. Also defined are functions that allow retr