Summary of Diameter Advantages over RADIUS

Better Transport

Diameter runs over a reliable transport, TCP or SCTP.
Lost packets are retransmitted at each hop.
A persistent connection with an application-level heartbeat message (called a Watchdog message) supports timely failover.
TCP and SCTP adapt to network congestion.
Better Proxying

Hop-by-hop transport failure detection allows failover to occur at the appropriate place — proxies can locally failover to an alternate next-hop peer.
The proxy automatically does retransmission of pending request messages following a failover.
An AVP that identifies the ultimate destination allows multiple transactions for a given session to be routed to the same home server.
Better Session Control

Session management is independent of accounting. Accounting information can be routed to a different server than authentication/authorization messages. Session termination is conveyed by a specific Session-Termination message rather than an Accounting Stop message.
The server may initiate a message to request session termination.
The server may initiate a message to request re-authentication and/or reauthorization of a user.
Better Security

Hop-by-hop security is provided using IPsec or TLS.
End-to-end security protects the integrity and/or confidentiality of sensitive AVPs through intermediate proxies.

原文：http://www.interlinknetworks.com/whitepapers/Intro_to_Diameter.htm

简而言之，Diameter是RADIUS的下一代，当然是一代更比一代强了，没时间细看，纪录先