EAP TLS: how the radius server track clients

Hi, I have a question about how the radius server keep track of clients in EAP TLS. My understanding is that EAP TLS involves a series of  requests/responses.  Hence the radius server needs to keep track of status for each client during the handshake. How does the radius server keep track of clients? Based on 'User-Name' in the radius packet request? Thanks Jim