[USR-TC] Unable to CHAP

i enabled chap authentication on HiperARC by : SET PPP AUTHENTICATION_PREFERENCE CHAP and SET PPP RECEIVE_AUTHENTICATION CHAP but it doesnt seem to work. i dialed into HiperARC by HyperTerminal and got login prompt but not chap challenge. how is it possible to enable chap authentication and disable pap? (i have HiperARC V4.1.59)