Linksys PAP2 audio issues only for incoming calls

[amaramrahul]

Hi,
I have been trying to figure out a solution to this problem for the past 10 hours but have so far been unsuccessful. Here is the problem.

I have configured my PAP2 adapter according to the voxalot PAP2 guide. I am able to make outgoing calls and everything works fine. But when someone calls my voxalot account via SIP Broker, I am unable to hear their voice though they can hear mine. Also if someone calls me directly using the SIP URI xxxx@eu.voxalot.com, audio is not heard both ways.

From what I've read on the forums, this mostly seems to be some NAT issue. But the strange part is that when I connect to the voxalot account either using X-lite (in Windows) or iSIP (in iPod Touch), there are no audio issues with incoming calls. Both the smartphone and the desktop PC are in the same LAN as the PAP2. Something advanced like MAC / IP based blocking cannot be the cause as my LAN is behind a simple ADSL router.

I have tried all possible configurations and yet am unsuccessful. Here are my current PAP2 settings:

SIP:
Handle VIA received: no
Handle VIA rport: no
Insert VIA received: no
Insert VIA rport: no
Substitute VIA Addr: yes
Send Resp To Src Port: yes
STUN Enable: yes
STUN Test Enable: no
STUN Server: stun.voxalot.com
NAT Keep Alive Intvl: 15

Line 1:
NAT Mapping Enable: yes
NAT Keep Alive Enable: yes
Make Call Without Reg: yes
Ans Call Without Reg: yes
Enable IP Dialing: yes

The remaining PAP2 settings are those whose are described in the voxalot PAP2 guide.

The interesting part is that previously I had set to port forward 5060 from the adsl router to my PAP2 device and then if someone called using the SIP URI xxxx@<public IP of router>, it worked without any sound issues.

I am thinking that there is some small configuration change I should do in PAP2 to resolve this issue. Any help would be really appreciated. Thanks.