[MAYBE OFFTOPIC] Modem hangup?

[Chaiya Intasoie]

Hello all;
        I'm not sure if this is the right list? I tried linux-ppp,
linux-serial but got no answer here is my question.

        I am trying to connect to my ISP using the modem to dial-in to the
ISP. 
        How can I re-dial when the modem hangup. I want the box (linux) to
check every if the modem is still connect or not. If the modem hangup then
re-dial to ISP automatically. Can anyone point me how to set this up.
Should I switch to diald instead of pppd?

Thanks for any help.
Chaiya