Panasonic KX-HTS Series Setup Reference Manual page 11

 SIP Trunk Property continued – SIP Carrier-1
[Session]
9. Session Timer Ability:
10. Session Expire Timer:
11. Session Incoming Refresher Request:
12. Session Refresh Method
[DSP]
Leave Default
[Option]
Leave Default
Click [Apply]
Click [Apply Now]
 Save the System data
Click [Save & Logout]
Leave Enabled (Passive)
Leave at 180
Leave UAC
Leave re-INVITE
11