local ringback from SBC to lync 2010

Hi guys

i'm having an issue with no ringback on a client lync 2010 , below u can see the  scenario in my test lab here at my work office . 

if i call from a Lync client to the PSTN i can hear ringback but if i try for example to call an EP registered on the cucm or an EP registered locally on the Asterisk i don't hear ringback on Lync ,anyway i can see 180 ringing going to Lync side .

RFC 3960 says :

1. Unless a 180 (Ringing) response is received, never generate local ringing.
2. If a 180 (Ringing) has been received but there are no incoming media packets, generate local ringing.

3. If a 180 (Ringing) has been received and there are incoming media packets, play them and do not generate local ringing.