Two softphones on different computers share same public IP

[sl9280]

I would like to know if we can have two softphones installed on two different computers with individual FPL# that share the same public IP behind a router.

e.g.

Computer A:
Number 1: 1-403-123-4567
Internal IP: 192.168.10.100
UDP port for voice: 13000

Computer B:
Number 2: 1-403-123-4568
Internal IP: 192.168.10.101
UDP port for voice: 13000

Both can be registered successfully with FPL and be able to make outgoing calls individually.

However, when number 1 call number 2 or vice versa, the conversation can only substain for about 30 seconds and then it will lose one side of communication. e.g. Number 1 can hear number 2 but not the other way. Some time after another while, both sides cannot communicate but the phone status still in connection (i.e. not end call).

I suspect there is a conflict in the voice UDP port and end up losing communication. Can FPL advise how to setup two computers behind the same router share one public IP.

I tried to change the voice port of one of the softphone to 13001 and the problem go away. Both phones can then call each other and communicate without problem.

The difference is when call between FPL softphones, the originating softphone ring tone is "ring, ring" that is not like the ordinary ring tone "Dude dude.." (lower frequency) when making outgoing call to other phone.

Why I ask this, because there would be other members in the house that can have their own FPL numbers and some time they may need to call each other.