How does EAP-SIM module decide whether read keys from file or calculate by itself?

[lishuai zhao]

Hi, all
    After I studied the EAP-SIM and EAP-AKA parts, I have some doubts
and questions:
    1.I think the function eap_sim_sendchallenge is to calculate keys
and send to authenticator, then authenticator forward it to the
client.
    2.I think the function process_eap_sim_challenge is to check the
response and to decide weather to response with EAP-Success.
    3.As said in 1, the eap_sim_sendchallenge can calculate keys
itself, and also the rlm_sim_file module makes it can read keys from
file. How to decide which method to use?

    Waiting for your replies, thank you!

    Best wishes!
    Lanny Zhao