Which call processing agent is based on Cisco IOS software and works with ISR platforms?

Cisco Unified Presence Server is a standalone application server for presence and instant messaging services, not an IOS-based call processing agent.

Cisco Unity Connection is a dedicated voicemail and unified messaging server that runs on its own platform and is not a call processing agent.

Cisco Unified Communications Manager Express (CUCME) is built directly into the Cisco IOS software image and runs on Integrated Services Router (ISR) hardware, requiring no dedicated server. It provides full call processing, dial plan configuration, and telephony features for small to medium branch office deployments entirely from within IOS.

Cisco Unified Communications Manager (CUCM) runs on dedicated server hardware or virtual machines and is not based on Cisco IOS software.

Cisco Unified Contact Center Express is a contact center platform that runs on a separate application server and is not based on Cisco IOS or ISR hardware.