Over the past few years, the drive towards optimization and globalization of business activities has mandated the integration of various services, an increase in system scale, and the networking of a variety of systems. These requirements can only be satisfied by the introduction of systems that are able to accommodate and control multiple media and integrate LANs and PBXs synergistically. This paper proposes an architecture for next generation private networks called ANS (Areal Networking System) that is targeted at achieving flexible customization in an effort to meet a wide variety of user requirements as well as the ability to efficiently handle multimedia services. Based upon the clarification of various requirements on the ANS architecture, this paper defines two models for the ANS architecture. These models introduce modular building blocks in hierarchical structures that facilitate the custom design of networks. The key technologies for the ANS architecture are also discussed; for example, schemes for logically networking control functions by using virtual connections and a way to implement the LAN function.