The Route Switch Processor 4 (RSP4) is the main system processor for the Cisco 7500 Series Router. The RSP4 combines all of the routing and high-speed switching functions for the Cisco 7500 series router. The high-speed switching section of the RSP4 communicates with and controls the interface processors on the Cisco 7500's internal high-speed buses. This switching section determines the destination of a packet, and switches it based on that decision.