Asterisk<==>PSTN not Hangup!

Hi friends,

I have a problem need be helped!
My server is RedHat Linux EL, install asterisk and zaptel, i have a card TDM400p (1 port FXO and 1port FXS). Port FXO connect PSTN line.

The call incoming, from PSTN–>Asterisk, when PSTN Hangup then Asterisk not detect these signal, hence the call not terminate althrough PSTN party was Hangup.

How to asterisk detect these Hangup signalling,
Please help me!

Than’k so much, and regard!