Final answer:
Diameter is the AAA protocol based on RADIUS that supports Mobile IP and VoIP, offering enhanced security and scalability.
Step-by-step explanation:
The authentication, authorization, and accounting (AAA) protocol based on RADIUS that supports Mobile IP and Voice over IP (VoIP) is Diameter. Diameter is an enhancement of the earlier RADIUS protocol designed to better serve the needs of advanced IP networks and next-generation network services such as Mobile IP and VoIP. Diameter offers more robust security features, supports higher numbers of simultaneous user sessions, and has a more flexible protocol framework than RADIUS, making it suitable for modern telecommunications and network infrastructures that require a more scalable and extensible AAA solution.