EAP-SIM simulation, how does Freeradius calculate MAC value in AT_MAC attribute

[Tabibel Sami]

Hi,

I am working on the implementation of  an EAP-SIM supplicant,
when i send to freeradius a EAP-Response/SIM/Start packet i receive as
expected an EAP-Resquest/SIM/Challenge with AT_RAND (RAND value was
specified in users file [2]) and AT_MAC, after this I should calculate
MAC value and test if this value matches witch AT_MAC value sent by
freeradius.

my question is how freeradius calculate MAC value in AT_MAC atribute ?
or from wich source freeradius fill MAC value in the AT_MAC attribute ?

[2]: my eap-sim user is set in users file as below :

1262074920549791        Auth-Type := EAP, EAP-Type := SIM
        EAP-Sim-Rand1 = 0x39900000000000000000000000000000,
        EAP-Sim-SRES1 = 0x30112233,
        EAP-Sim-KC1 = 0x445566778899AABB,
        EAP-Sim-Rand2 = 0x31000000000000000000000000000000,
        EAP-Sim-SRES2 = 0x31112233,
        EAP-Sim-KC2 = 0x445566778899AABB,
        EAP-Sim-Rand3 = 0x32000000000000000000000000000000,
        EAP-Sim-SRES3 = 0x32112233,
        EAP-Sim-KC3 = 0x445566778899AABB

Thank you in advance,
Best regards.

--
Sami