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Diameter Protocol
Diameter is an Authentication, Authorization, and Accounting (AAA) protocol defined in RFC 3588, and a successor to RADIUS. It is used primarily in modern IP-based networks for carrying authentication, service authorization, and configuration information, especially within mobile networks and LTE infrastructure..
Diameter is a protocol designed to provide scalable AAA services in IP-based networks. Its design overcomes many limitations of its predecessor, RADIUS, including improved transport reliability, failover mechanisms, and enhanced security capabilities. Functionally, Diameter supports message routing, proxying, and redirect services, facilitating communication between diverse network entities in a flexible manner.
Diameter operates primarily over TCP or SCTP, aiming to ensure reliable data delivery rather than the unreliable transport used by RADIUS. The protocol defines a base message structure with extensible commands using Attribute-Value Pairs (AVPs), allowing it to be adapted for new applications without breaking backward compatibility. This extensibility makes Diameter suitable for a variety of AAA scenarios, from LTE core network functions (like S6a interface) to IMS implementations.
In mobile networks, Diameter functions as a fundamental signaling protocol handling subscriber profile management, mobility management, charging, and policy control. Interfaces that rely on Diameter facilitate communication across Home Subscriber Servers (HSS), Policy Charging Rules Functions (PCRF), and other critical infrastructure elements, ensuring consistent subscriber experiences and seamless roaming.