[USR-TC] Callback on HiPer

I have chassis with HiPer ARC (5.3.3), HiPer DSP E1/PRI (3.5.13). I want to do callback on that TC. Callback is enabled on HiPer ARC (enable ppp negotiated_callback), interfaces are TWO_WAY. On radius there is user with Service-type Callback-Framed, Callback-Number xxxxxx, and all other attributes for network user. After calling this TC, callback is negotiated and TC calls me back, but my modem can't hear TC side modem. Where is problem? Can anybody help?