[Users] sdp negotiation fails - no ACK - rtpproxy

Benko benkokakao at gmail.com
Tue Mar 6 14:29:23 CET 2007


Hello!

I'm struggling with a issue since several days, since i make no more
efforts i'd like to ask you for help: 
I'm trying to attach a exchange 2007 server to openser, most of the
features work(inbound call, refer) but i can't get a outbound call to
work as exc doesn't seem to like the SDP in my "200 OK" answer, i get no
ACK and no rtp-stream is sent from exchange. My setup looks like this:

    ________         _______        _____         ________
   |asterisk|=======|openser|======|(NAT)|=======|exchange|
   |________|       |_______|      |_____|       |________| 
   2x.x.x.107       2x.x.x.106    62.x.x.193      10.1.99.97


A rtpproxy is running on the openser too, exchange is talking tcp...


In my openser-config i use the nathelper-module and rtpproxy to
traverse nat for the clients. This setup is working for all phones i've
tested so far, so imho it is useable.

Exchange has a feature that allows dialouts to read voicemail to e.g.
a mobile phone. It is using a standard INVITE dialog, in a local
network without nat i've been succesfull to attach exchange to sipx and
a phone registered at sipx and i guess it will also work with a local
openser who doesn't use nat-traversal features.

However, with the public openser where i have a NAT, exchange doesn't
seem to accept my sdp-proposal, i get no ACK and the rtp stream is only
sent by asterisk, not by exchange. 
Unfortunately exchange offers no valuable debugging information, so i
have no idea what exactly it doesn't like about my answer - i did some
trial and error with different nat-helper-functions, activated and
deactivated them but so far it didn't make a difference(or the call
didn't got through at all due to missing nat-traversal).

I've uploaded wireshark-traces exported to text of the
working local dialog with sipX(http://pastebin.ca/383516) and the
non-working external dialog (http://pastebin.ca/383540) with
openser, maybe someone can take a look at it and check if
there's something wrong on my(=openser) side of the dialog - Thanks in
advance!

best regards
Christian




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