My VOIP Trunk provider (voiptalk.org) specifies RTP 10000-20000. I have this set in my “Asterisk SIP Settings”, RTP Port Ranges.
I wish to install an external SIP phone (Grandstream BT200) on a public internet address behind a NAT. On the Grandstream “Advanced Settings” page, the default RTP port specified is 5004. (Must be even).
My questions are:
Can the Grandstream RTP port stay at this default and I simply forward the SIP and RTP port 5004 through the NAT, or do I have to change the default RTP port to somewhere within the range defined in the Asterisk Server (10000-20000)?
Do I need to enable Symmetric RTP in both the FreePBX Extension configuration AND at the SIP Client?