Found this at iinet support pages for their VOIP setup.

UDP 5060: From sip.state.iinet.net.au
UDP 35000-44999: From sip.state.iinet.net.au
UDP CPE Port: The port your CPE uses for RTP, eg 8000-8001 or 5061 or 16384 for Netcomm V300 firmware v04
I have no problems with first two ports configuration. The last one UDP CPE port I don't understand at all.
What is it? What is CPE and how I can find out wich port my PAP2 ATA uses for RTP?
I assume CPE is customer premises equipment - ATA PAP2 in my case.