I have seen complaints that Polycom SoundPoint IP phones do not work well with NAT. The problem is the port used for RTP gets closed on the firewall after a while and the phone doesn’t know about it. Then calls go through, but the user gets dead air. A relatively harmless workaround is to have the phone re-register every 30 seconds. Then the port refreshes at an interval low enough that the firewall never closes it.
I found a reference to a very simple fix and have had success with it: Simply edit the .cfg file for the phone (assuming the phone is getting its settings from TFTP or FTP) and change the following value: reg.1.server.1.expires=”" to reg.1.server.1.expires=”30″
If you have other configured lines, then you’ll also need to change reg.2.server.1.expires, reg.3.server.1.expires, etc.
I’ve also had problems with the RTP ports being used falling outside of the range specified on the firewall’s port mapping, which caused the same symptoms. The phone started at port 16844. I just just adjusted the firewall, but there are also settings on the phone to force the RTP port or port range used.
This worked for a Polycom 501, but should be the same for any of the SoundPoint IP models: 300, 301, 500, 501, 600, 601.
Posted by Pat McKay 
