Most of the routers will automatically forward the incoming traffic to the appropriate softphone or the adapter. Some routers are very restrictive and some users might have a firewall which you might have to configure. Also, if you have any port forwarding that will come in the picture too..
Generally speaking, don't DMZ, dont port forward and see if everything works correctly. I don't do any of these. You might hit some problems when there is a port conflict on your end. This can be fixed by using STUN, setting rport field etc..
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