What are the different functional Diameter nodes?

The following are the various functional Diameter nodes:

• Diameter Client - A diameter client is the one that initiates the user authentication/authorization request. Typically, Network Access Servers act as Diameter clients.
• Diameter Server - A diameter server authenticates the users, by looking at the user database. If the authentication is successful, user profile information is sent to the Diameter client. Otherwise, a "reject" message is sent to the Diameter Client.
• Diameter Relay Agent   - A relay agent is used to forward protocol messages to appropriate Diameter Server. A relay forwards the message to the Diameter Server "as-is". It eliminates the need for the Diameter Client to maintain information about different Diameter Servers. The Diameter client can always forward requests to the Diameter Relay Agent, which in-turn decides the right Diameter Server for the request based on the realm.Thus, any time a Diameter Server changes, the network administrator doesn't have to modify the configuration in 100s of Diameter Clients. The configuration change has to be performed in just the Diameter Relay Agent.
• Diameter Proxy Agent - The function of the Diameter Proxy agent is very similar to that of the Diameter Relay Agent. However, the Diameter proxy can modify message content and apply rules.Thus, a Diameter Proxy can be used to enforce rules on different messages or perform administrative tasks for a given realm.
• Diameter Redirect Agent  - A redirect agent maintains request/response routing information in a central location. A redirect agent is used to redirect a Diameter client  (or a proxy or a relay) to the appropriate Diameter server. A redirect agent serves as a centralized configuration repository. The difference between the Relay and Redirect agent is - the Relay agent forward the request to the appropriate Diameter Server based on the request routing configuration, whereas, the Redirect agent sends routing information to the client and the client then contacts the Diameter server, directly.
• Diameter Translation Agent - A translation agent helps a service provider to migrate from a RADIUS/TACACS based authentication infrastructure to the Diameter based authentication infrastructure. The translation agent can convert a RADIUS request/response to a Diameter request/response, respectively and vice versa.