This paper describes the application of a general purpose object-oriented software engineering method to the design of a bandwidth management system for ATM-based virtual private networks (VPNs). Such a system allows a VPN customer to dynamically modify the bandwidth allocated to VPN connections. The design process has focused on the service management information model and interfaces required to provide that service to the customer. Object interaction graphs have been designed and class descriptions have been derived. Finally the VPN customer, value added service provider and network providers service management system interfaces have been designed and corresponding primitives are given.'