Which protocol improves upon RADIUS (Remote Authentication Dial-in User Service), strengthening some of its weaknesses, but is less widespread due to fewer products using it?

Diameter is the protocol that improves upon RADIUS by addressing some of its weaknesses, such as scalability, security, and flexibility. Diameter supports authentication, authorization, and accounting services but does so with enhanced features compared to RADIUS. For instance, it utilizes TCP or SCTP for transport rather than UDP, which provides reliable message delivery and avoids issues related to connection management inherent in RADIUS. Additionally, Diameter allows for more complex authentication methods and supports richer data formats, improving its capability to manage different types of network access.

However, despite these improvements, Diameter has not been adopted as widely as RADIUS, primarily due to the existing investment in RADIUS technology and the ecosystem built around it. As a result, many vendors and products still rely on RADIUS, leading to a slower adoption rate of Diameter in the industry. This context underscores why Diameter is recognized as an enhanced version of RADIUS but remains less prevalent in practice.