Centralized and distributed approaches to the design and implementation of a multi-gigabit per second asynchronous transfer mode (ATM) switch are discussed. The implementation constraints associated with a centralized switch are demonstrated and an alternative distributed optical network architecture is described. The distributed approach exploits unique opportunities presented through the use of a passive optical medium. A network based on these principles (TeraNet), has been implemented that offers user access rates of 1 Gbit/s. The distributed ATM switch fabric resides in small, geographically dispersed access stations interconnected by a shared, all-optical medium carrying many wavelength-multiplexed channels. Although the underlying multihop architecture for the ATM network produces a lower per-port throughput than that afforded by a large centralized ATM switch, significant implementation advantages exist. Possible techniques to yield a higher per-port throughput approaching that of a large centralized switch are also discussed.>

Abstract TeraNet is an experimental network being built at the Center for Telecommunications Research, Columbia University. The network is part of the ACORN (Advanced Communications Organization for Research Network) project. The purpose of ACORN is to investigate innovative optical network architectures which offer user access at data rates as high as one Gigabit per second (Gbit/s). The design principles of TeraNet incorporate three main concepts: a transmission medium that contains multiple channels; a system architecture that employs a multihop approach to routing packets; and a traffic control architecture that supports multiple traffic classes. The network contains a set of network interface units (NIU) that are interconnected with passive optics. Each NIU is a two-by-two switch with an additional user access port. Each of the six NIU ports (three input and three output) can handle data rates up to one Gbit/s. The NIU buffers and the bandwidth of the output links are shared by four traffic classes according to the ATS concept of resource allocation. The packet format and routing procedure are compatible with the emerging ATM standard.

MAGNET II is a testbed for integrated networks. It was designed and implemented based on requirements of real-time network management and control. Quality-of-service requirements explicitly appear in the design specifications of the network on the media access level. Switching is based on the concept of asynchronous time sharing. The core of the network distinguishes between three traffic classes. The quality of service of these classes is monitored and controlled by the traffic-control architecture of the network. Monitoring is supported by observation units distributed throughout the system. The main network resources, switching bandwidth, communication bandwidth, and buffer space, are observable and controllable.>