The objective of this draft is to clarify a framework for standardizing the mechanisms supporting interoperable network-based virtual private networks (NBVPNs). These are VPNs using IP facilities whose operation mechanisms are implemented within a network (or networks) and outsourced to one or more service providers. This draft first describes the assumed services of NBVPNs and clarifies the logical architecture model and reference model of NBVPN. Considering the assumed services, this draft further clarifies the NBVPN requirements for interfaces and MIBs in the reference model. It also surveys and discusses current technologies supporting NBVPNs such as tunneling, VPN identifier, routing, and QoS/SLA. Additionally it will, in future, provide outline of the interface and MIB specifications and present criteria for achieving interoperability.