OH323 Fake Ring

Hi All,

I need your urgent help.
i installed OH323 channel and it is working well with samll problem fake ring.
I have my VoIP provider MCI and AT&T when i am routing the call via OH323 from the SIP ATA like Linksys i am getting too much fake ring even some time real RBT is there and also i can hear fake ring.

Could u please guide from which configuration i can disable the fake ring. one thing more funny when i am dialing using SIP channel to these provider i am not getting any fake ring, just we are getting real RBT.

this is my dial option:

AGI Script Executing Application: (Dial) Options: (OH323/MCI/phone-number|350|S(max talk time))