I successfully tested SIP/RTP using a SIP Soft Phone , a VPN and VZW 4G-LTE network, my laptop with the Pantech UML295 4G-LTE modem.
Now, I want to do the same SIP/RTP tests without the VPN and just using the destination phone number (toll-free) and the MDN.
Is this possible with VZW 4G/LTE and the UML295 modem?..
I tried it, but without the VPN, the SIP Invite and its retries times-out and never gets any responses (Ringing, Trying or other).
The backend servers I am trying to connect to are not public IPs.so I cant specify them. A media gateway maps the call to
proper the backend servers. The toll-free number and backend services I am trying has been in-place and working for years.
The MDN is in the SIP Invite header.
How might this be done?
