[Freeswitch-users] Freeswitch as b2bua

Helmut Kuper helmut.kuper at ewetel.de
Wed Feb 28 01:01:05 PST 2007

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I want to know whether freeSWITCH is able to be a b2bua proxy for both
sip and rtp or not. sofia has a registration section to Register
freeswitch to one or more upstream VoIP provider. I understand this
feature in that way, that UAC registered to freeswitch can use this sip
accounts to do outbound calls into a external VoIP-Cloud/domain. My
picture of it is as follows:

1. uac1 at mydomain.com makes an outbound call to uac2 at externaldomain.com

2. freeswitch gets this call, answered it and sets up a RTP stream to uac1.

3. freeswitch uses the destination address of uac1 and establish a call
as a member of externaldomain.com eg. freeswitch at externaldomain.com.

4. freeswitch bridges the RTP stream between uac1 and freestwitch's own

This means uac1 is only talking to freewitch while freeswitch is talking
to uac1 destination. So freeswitch acts like a man in the middle.

Am I wrong ?

In my test environment freeswitch registers to the upstream provider,
but when I start a call from uac1 to a uac in that upstream provider
domain. freeswitch takes it and send an invite to upstream. In this
invite message I can find a source sip address which is that from uac1
instead of freeswitch's registration account for upstream domain. The
upstream sip proxy sends first a Trying and then a 488 message "Invalid
Session Description". The 488 message contains a Warning named "
Warning: 301 xxx.xxx.xxx.xxx 'invalid transport IP address'"

I think this reffers to the forwarded uac1 source sip address, so that I
think that the upstream sip proxy doesn't accept source addresses which
doesn't belog to that upstream sip domain.

Any ideas how I can convince freeswitch to act as a UAC-Proxy for rtp
and sip?


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