Xunet 2: lessons from an early wide-area ATM testbed

This paper is a retrospective on the design of Xunet 2, one of the earliest functional wide-area asynchronous transfer mode (ATM) networks. Work on Xunet 2 began in 1989 and the network, consisting of experimental ATM switches, IP routers, and 45 Mb/s transmission lines, has been operational since October 1991. The network serves as a "laboratory without walls" for eight research groups across the United States. While Xunet 2 has only a small number of nodes, it was designed as a prototype of a nationwide ATM network. This paper reviews some of the design decisions and lessons learned in the project and points out the research directions motivated by this work, focusing on the areas of traffic management, ATM switch design, network control, and the implementation of an IP router.