Strange behaviour of codec-negotiation

31 Oct 2012

      Hey guys!

I have a real problem with FreeSWITCH (latest GIT) and the codec negotiation. I tried all, even did packet-capturing with wireshark. Something goes wrong with negotiation. First of all an overview:

Siemens OpenStage (Phone) <-- internal-profile --> FreeSWITCH (Gateway) <-- external-profile --> FRITZ!Box 7270 (Gateway)

Siemens OpenStage codec-order:
G722,PCMA,PCMU,G729

FreeSWITCH internal-sofia-profile:
<param name="inbound-codec-prefs" value="G722,PCMA,PCMU"/>
<param name="outbound-codec-prefs" value="G722,PCMA,PCMU"/>
<param name="inbound-late-negotiation" value="true"/>

FreeSWITCH external-sofia-profile:
<param name="inbound-codec-prefs" value="G722,PCMA,PCMU"/>
<param name="outbound-codec-prefs" value="G722,PCMA,PCMU"/>
<param name="inbound-late-negotiation" value="true"/>

1) When I originate a call to a cellphone from the Siemens OpenStage, the phone offers G722, PCMA, PCMU and G729 in the INVITE to FreeSWITCH. All ok!
2) FreeSWITCH forwards this INVITE to the FRITZ!Box 7270. All ok!
3) FRITZ!Box 7270 answers the INVITE with a "100 Trying" to FreeSWITCH. All ok!
4) FRITZ!Box 7270 sends a "183 Session progress" with SDP to FreeSWITCH and offers G722, PCMA and PCMU. All ok!
5) FreeSWITCH sends this "183 Session progress" with SDP to Siemens OpenStage and offers only G722. All ok! At this stage, the codec is negotiated and I can hear the ringing (early media) without any problems.
6) When picking up the call on the cellphone, FreeSWITCH receives a "200 OK" with SDP from FRITZ!Box 7270. In the SDP there is codec-change and the FRITZ!Box 7270 now offers only PCMA and PCMU.
7) FreeSWITCH sends an "ACK" to FRITZ!Box 7270.
8) FreeSWITCH sends the "200 OK" to the Siemens OpenStage but still offers only "G722" and not the "new" "PCMA, PCMU".
9) FRITZ!Box 7270 sends an "ACK" to FreeSWITCH.
9) FRITZ!Box 7270 sends its media still in G722.

The result is:

The Siemens OpenStage does not receive any packets and there is a complete silence on the phone.
On the cellphone, I receive a complete distorted voice. It sounds like a "kidnapper".

Wireshark shows the following with the rtp-media:

FreeSWITCH  --G722--> FRITZ!Box 7270
FreeSWITCH <--PCMA--  FRITZ!Box 7270

Siemens OpenStage -----G722--> FreeSWITCH
Siemens OpenStage <--no packets-- FreeSWITCH

Can anybody help? Why does FreeSWITCH don't propogate the second SDP (with the "200 OK Message") to the Siemens OpenStage?

Alex

"Alex Müller"

Anthony Minessale

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