How to fix call being dropped after 5 minutes?

Hi guys im just new in using elastix. i have experience that whenever someone is calling this specific extension the call gets drop after 5 minutes or sometimes calls randomly drop.

from what ive observed it seem like when this extension calls other extension it is ok. it does not disconnect.

how do i check for the problem??

thanks in advance guys

Elastix support forums are available at they use a modified version of FreePBX that is not supported by this community.