[Freeswitch-users] Probably obvious but not to me - sofia hangup

Hi, I am on freeswitch / centOS: Linux pbx 2.6.18-194.11.3.el5.centos.plus #1 SMP It is a fairly straight out of the box freeswitch config, I am not so good with XML yet. Issue is the line to my single SIP phone will drop after about 8 minutes, no matter if talking or not. What might be the cause of this? Seems like a timeout or lack of ACK somewhere? Thanks for the help.... Mark B