stripped-username for eap sim

Hi all, i'm using freeradius 2.1.9 for eap sim testing i have simtriplets.dat with format : imsi.RAND,SRES,Kc and i'm having message probleme: rlm_sim_files : insufficient number of challenges for imsi 151008xxxxxxxxx@wlan.mnc008.mcc310.3gppnetwork.org [sim_files] : returnnot found i read that we should strip that full username : 151008xxxxxxxxx@wlan.mnc008.mcc310.3gppnetwork.org into strip username: 131008xxxxxxxxx and realm wlan.mnc008.mcc310.3gppnetwork.org am i correct? so how do i configure that strip username for authorizing into rlm_sim_files and to simtriplets.dat? thanx best regards, martin