Architectures With Bus‐Based Switch Fabrics: Case Study—Fore Systems Powerhub Multilayer Switches

This chapter describes the architectures of the Fore Systems PowerHub multilayer switches [FORESYSWP96]. The PowerHub multilayer switches (PowerHub 7000 and 6000) perform both Layer 2 and Layer 3 forwarding and support a wide range of physical media types for network connectivity. The chapter covers architectures with bus‐based switch fabrics and centralized forwarding engines and, architectures with bus‐based switch fabrics and distributed forwarding engines. The PowerHub supports four CPUs with its software designed to run in a multiprocessor system. In the PowerHub, six separate processes service each packet forwarded by the system, with the processes communicating through first‐in first‐out (FIFO) descriptor queues. They are packet reception, receive polling, forward polling, transmit polling, packet transmission and transmit cleanup. A majority of the first‐generation switches and routers were often designed based on shared bus and shared memory architectures with a single, centralized processor.