This paper is a draft of a technical report that was never published. AN2 is a high-performance Asynchronous Transfer Mode (ATM) switch developed at Digital’s Systems Research Center. AN2 provides sixteen 800 Mbit/sec. porls, each of which can contain a 4-port 155 Mbitlsec (Oe·3) line card, or a single 622 Mbit/sec. (OC12) line card. AN2 supports both constant bit rate (CBR) and available bit rate (ABR) traffic. It uses a unique hop-by-hop flow contra] prolocollhal eliminates cell loss. even in the presence of congestion. Software in the switch provides circuit setup functions, automatic network reconfiguration in the event of hardware failures, and resilient virtual circuits, which provide automatically-established connections in a local area ATM network of modest size. AN2 is the prototype for Digital’s ATM switch products. In this paper, we discuss the implementation of the hardware and software of AN2.