Cisco 4000 Series Integrated Services Routers (ISR), the branch routers, is a digital-ready platform that offers at least 4 GE ports, 3 NIM slots, 2 SM slots and 8 CPU core ISM slots. Cisco 4000 Series include ISR4221, ISR4321, ISR4331, ISR4351, ISR4431, ISR4451 series.