Protocol and operating system overheads have become the limiting factor for communications performance on fast networks such as ATM. A large component of these overheads stems from the protocol redundancy that arises when layering higher level protocols on top of lower level ones. ATM, for example, requires specific mechanisms for connection management, flow control, congestion avoidance, and segmentation and reassembly. With these mechanisms in place, it is relatively simple and inexpensive to provide for reliable sequenced delivery at the network interface level, making similar functionality in higher-level protocols such as TCP/IP redundant. In this paper we present a protocol architecture specifically tailored for communication over high-bandwidth low- latency local or metropolitan ATM networks. Our architecture yields high performance by eliminating protocol redundancy and by exploiting common-case communication behavior. With this approach, we can combine the functionality typically found in four separate layers of the ISO model-data link through session-in a single pass over the data, delivering high throughput and low latency