An important challenge for the future growth of the Internet is to design routers that can forward the exponentially increasing volume of tra c, and at the same time provide the service di erentiation needed by new applications. In this paper, we describe the architecture, implementation, and initial experiences with a system designed to meet this challenge. This system, which we call a QoS capable Switch-Router (QSR), combines the salient features of switching and routing technologies to provide high throughput and support the di erent classes of service being de ned by the IETF. It consists of a core (ATM) switch fabric connecting intelligent adapters, each capable of both routing and switching packets. A control engine is responsible for routing, RSVP signaling, and resource management. We have built a prototype network of 3 systems connected to several UNIX hosts, and have conducted preliminary performance measurements on this network.