When the session is complete, the network access server sends another Accounting−Request packet to the RADIUS security server, detailing the delivered service. Because RADIUS implements services using the UDP protocol (which is connectionless oriented), the RADIUS server has the responsibility of acknowledging the Accounting−Request packet with an Accounting−Response packet. This is considered the Accounting−Start packet. It is the network access server's responsibility to send accounting information to the RADIUS server after initial authentication and authorization is complete, and it does so by sending an Accounting−Request packet to the server.
The network access server and RADIUS server communicate accounting information between one another on UDP port 1646.
