As enterprises use ATM networks for their private networks and as these private networks use public ATM networks for wide area communication, the need for the customers to be able to manage both private and public networks is increasing. Currently, some standardization work is being done towards providing this capability to customers. In this paper, we propose a new customer network management (CNM) system architecture for the management of both private and public ATM networks in a uniform way. The particular features of the proposed architecture lies in the efficient support of the complex hierarchical TMN manager-agent relationships at M3 and M4 interfaces, and the support of SNMP and CMIP integration. The TMN hierarchical many-to-many manager-agent relationships are realized by the utilization of a CORBA-based Shared Management Knowledge (SMK) system. We have implemented a prototype of ATM CNM system, and measured the performance for the demonstration of the suitability of the proposed architecture.