Redirect Agent

            A Redirect Agent acts as a centralized configuration repository for other Diameter nodes. When it receives a message, it checks its routing table, and returns a response message along with redirection information to its original sender. This would be very useful for other Diameter nodes because they won't need to keep a list routing entries locally and can look up a Redirect Agent when needed. Figure 3 illustrates how a Redirect Agent works. The scenario in Figure 3 below is basically identical to the one in Figure 2, but this time the Proxy Agent is not aware of the address of the contacting Diameter node within example.com. Therefore, it looks up the information in the Redirect Agent of its own realm to get the address.

Translation Agent

In addition to these agents, there is a special agent called Translation Agent. The responsibility of this agent, as you might have guessed, is to convert a message from one AAA protocol to another. The Translation Agent is helpful for a company or a service provider to integrate the user database of two application domains, while keeping their original AAA protocols. Another situation is that a company wants to migrate to Diameter protocol, but the migration consists of many phases. The Translation Agent could provide the backward capability for a smooth migration. Figure 4 shows how one agent translates the RADIUS protocol into the Diameter protocol, but, of course, other kinds of protocol translation (for example, Diameter to RADIUS, Diameter to TACACS+) are also possible.