Explanation:
The ATM Forum has defined as management interface architecture, ATM network reference model. There are five interfaces between systems and networks, M1, M2, M3, M4 and M5. Ml and M2 are, respectively, the interfaces between private NMS and either end-user of private network. A private NMS can access its own network-related information in a public network via an M3 interface to the public NMS. M4 is the interface between a public NMS and a public network. M5 is the interface between NMSs of two service providers.