The Cisco 4000 Series Integrated Services Routers (ISRs) provide advanced routing, security, unified communications, and application services for enterprise branch offices and campuses. This router series includes the Cisco ISR 4321, 4331, 4351, 4431, and 4451 models.

Key features of the Cisco ISR 4000 Series include: high-performance routing with up to 300 Mbps throughput, modular design, dual embedded service modules, network virtualization, encrypted traffic analytics, and advanced threat protection. The routers run on the Cisco IOS XE operating system which provides a broad range of features and flexibility.

The Cisco ISR 4000 Series utilizes a modular architecture that allows customers to customize the router by adding various interface modules, security modules, and application service modules. Overall, the ISR 4000 Routers deliver a comprehensive enterprise-class solution for mid-sized sites.