Skinny phones does not detect DTMF

i designed a telephony system with asterisk , i have some sip phone and some other 7960 cisco phones ,i use tenor as the gateway . my problem is with DTMF detection , at first all telephones could not send DTMF but when i set the DTMF of sip phones to info the problem solved for sip phones . but the cisco phones still have problem . i set dtmfmode option in skinny.conf to info and rfc2833 but they still have problem .
i also test diffrent kind of DTMF option is for sip trunk between asterisk and tenor but it fails .
any idea to solve this ?