HP-UX AAA Server A.08.01 administrator's guide (T1428-90072, May 2010)

Figure 1-2 Client-Server RADIUS Transaction
When the user's device connects to the client, the client sends a RADIUS Access-Request
to the AAA server. When the server receives the request, it validates the sending client.
If the client is permitted to send requests to the server, the server then takes information
from the Access-Request and attempts to match the request to a user profile. If all
conditions are met, the server sends an Access-Accept packet to the client; otherwise,
the server sends an Access-Reject packet. An Access-Accept data packet often includes
authorization information that specifies the services the user can access and other
session information, such as a timeout value that indicates when the user must be
disconnected from the system.
When the client receives an Access-Accept packet, it generates an Accounting-Request
to start the session and send the request to the server. The Accounting-Request data
packet describes the type of service being delivered and the user of the service. The
server then responds with an Accounting-Response to acknowledge that the request
was successfully received and recorded. The user's session ends when the client
generates an Accounting-Request that is triggered by the user, the client, or an
interruption in service-to stop the session. The server acknowledges the
Accounting-Request with an Accounting-Response.
Establishing a RADIUS Session 37