Diameter Client - A Diameter Client is a node at the edge of the network that performs access control.
Diameter Server - A Diameter Server handles authentication, authorization, and accounting requests for a particular realm.
Relay Agent - It is used to rout the message to other diameter node with the help of routing information received in message such as Destination-Realm, Destination -Host. Relay can accept the request with multiple networks.
Relay must not change message format and avps except the routing avps. Relay must advertise its Application Identifier (0xffffffff).
Proxy Agent - Diameter Proxy does all that relay does. Moreover proxy can change message and avp format if required to apply some policies.
A Diameter Proxy MUST be called as DIAMETER X Proxy, where X is the application whose messages are being proxy-ed by by the node.
Redirect Agent - Diameter Relay is useful in the scenario where diameter routing information is stored at centralized location. Every node can get the rout information from Redirect agent and then forward the message. Redirect Agent does not forward message to any node. It just replies to the request received with the routing information
Redirect must advertise its Application Identifier (0xffffffff)
Translation Agent - A Translation Agent translates between two protocols, such as RADIUS and Diameter. In this case, the translation agent supports a RADIUS to Diameter migration, allowing server conversions to Diameter.
Edge Agent - A Diameter Edge Agent provides the extra security communications service providers (CSPs) require to connect securely with third-party partners when needed and share resources, such as in roaming and billing use cases. It does this by enabling Diameter signaling messages to flow smoothly among networks while also adequately disguising the topology of both networks. Its normalization engine ensures that only supported AVPs (attribute-value pairs) and content enter the network. It can also protect Diameter servers and the entire network from overload conditions brought on by DoS attacks or other types of traffic overload.