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<p><font size="2" face="Tahoma">Hi All</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">We're quite new to Freeswitch and are in the process of migrating from OpenSer (as an SBC) to Freeswitch.</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">Mostly all is working well, except an oddity on DTMF.</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">Our scenario:</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">Telco/SIP Provider A is passing us calls using DTMF inband.</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">We have a freeswitch configured as a SBC using 2 sip profiles (telco and internal) to topology hide and manage</font></p>
<p><font size="2" face="Tahoma">distribution of calls to the PBX servers located behind the SBC.</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">The freeswitch will be handling up to a few hundred calls so we're trying to keep it lightweight.</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">Behind the SBC is a series of Asterisk and Freeswitch PBX boxes handling customer needs.</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">An example inbound call profile looks like this:</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma"><extension name="Inbound 124356"></font></p>
<p><font size="2" face="Tahoma"> <condition field="destination_number" expression="^(123456)$"></font></p>
<p><font size="2" face="Tahoma"> <action application="pre_answer"/></font></p>
<p><font size="2" face="Tahoma"> <action application="start_dtmf" /></font></p>
<p><font size="2" face="Tahoma"> <action application="bridge" data="<a href="mailto:sofia/external/123456@INTERNAL.PBX.IP:5060%22/">sofia</a><a href="mailto:sofia/external/123456@INTERNAL.PBX.IP:5060"/">/external/123456@INTERNAL.PBX.IP:5060"/</a>></font></p>
<p><font size="2" face="Tahoma"> </condition></font></p>
<p><font size="2" face="Tahoma"></extension></font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">Initially when calling into the platform IVR type applications runinng on our PBX boxes would not</font></p>
<p><font size="2" face="Tahoma">work (you could hear the DTMF but the platform did not recognise the tones).</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">We have had to add the appliation start_dtmf in order for Freeswitch to pass the DTMF to the Asterisk</font></p>
<p><font size="2" face="Tahoma">PBX behind the SBC. Interestingly on our OpenSer platform we just proxied the media (rtpproxy) with</font></p>
<p><font size="2" face="Tahoma"><font size="2" face="Tahoma">inband</font> DTMF from the Telco and our PBX boxes recognised the inband DTMF tones on the PBX platforms and</font></p>
<p><font size="2" face="Tahoma"><font size="2" face="Tahoma">IVR</font> type applications just worked.</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">However under freeswitch if we don't start_dtmf before the bridge the backend PBX boxes don't recognise</font></p>
<p><font size="2" face="Tahoma">the DTMF inband (even though the tones are audible ie you can hear them on a call recording on the</font></p>
<p><font size="2" face="Tahoma">PBX).</font></p>
<p><font size="2" face="Tahoma"> </font></p>
<p><font size="2" face="Tahoma">Have we missed something here? We would have thought with inband DTMF on non compressed codec (no
</font></p>
<p><font size="2" face="Tahoma"><font size="2" face="Tahoma">transcoding</font>) that the tones would just work with the media stream?</font></p>
<p><font size="2" face="Tahoma"><font face="tahoma"></font> </p>
<p></font><font size="2" face="Tahoma">We have confirmed both legs are PCMA and when using start_dtmf the first second of the call is clipped.</font></p>
<p><font size="2" face="Tahoma"></font> </p>
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<div><font size="2" face="Tahoma">Kind Regards,</font></div>
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