Cisco 8831 Administration Manual page 37

Chapter 3 Configure SIP and NAT
The service provider might require the phone to send NAT keep alive messages to keep the NAT ports
open. Check with your service provider to determine the requirements.
Step 6 Click Submit All Changes.
Configure the firewall settings on your router to allow SIP traffic. See the
Step 7
page 3-4.
Cisco Unified IP Conference Phone 8831 for Third-Party Call Control Administration Guide
Configure NAT Support Parameters
"Configure SIP" section on
3-11