[Linphone-developers] [help] Linphone using proxy in a VPN without registration

[buch]

Hi,

I didn't found another way contacting people with a bigger background 
knowledge about linphone. I hope the mailing list is fine for this purpose.
I am trying to get linphone to work with a speech application which I 
can only connect to via a VPN network. Thus I have 2 CIDR addresses. A 
private IP and the VPN IP.
When I configure linphone to connect to the speech application I have 
following setup:
[image url: http://postimg.org/image/735j9maix/]
If I choose my ip address in the vpn subnet instead of localhost, the 
call also fails (exact symptoms below).

The call does not time out or something. I can call and the speechapp 
will answer the call but don't play the prompt. If I hang up, it also 
acts normal. Just that there is no prompt being played.
I used tcpdump on the speech application machine ('#  tcpdump -i any udp 
port 5060 -nnv') and compared it with the output of X-Liste v5 which is 
able to connect to the speech application (with prompt, as you would 
expect it).
You can find the two logs enclosed.
From SIP segment perspective everything is working fine (invite, 
ringing, ok,  ack, bye, ok) but the VIA attribute of the SIP segment is 
using my local IP address instead of the VPN IP address, which X-Liste 
uses.

Can this be the issue why no prompt is being played? And if this might 
be the issue: Can you tell me how I can configure this in linphone? Or 
at least confirm me, that this kind of configuration is not possible?
I really need to connect via the VPN. This is sadly not optional.

I would be really glad hearing from you.
Thanks in advance

Christian

#################### Attachment ##############
[1] Linphone call tcpdump:
http://pastebin.com/NEy3CJbj
[2] X-Lite v5 call tcpdump:
http://pastebin.com/zs1RyNGj