[Freeswitch-users] Inbound 1-way audio issue using GSM codec

[Maxim Karp]

Hello,

I am using a GSM based endpoint connected to freeswitch that makes calls to
the PSTN via a SIP gateway (SBC).  The SBC uses PCMU between itself and
freeswitch.

When I make an outgoing call from a GSM based device via freewsitch to the
PSTN via the SBC, everything works fine and audio works in both directions
for both end points.  I looked at the console logs and they do indicate that
I am using GSM.

Console output when I dial and before answer on the GSM device:

v=0
o=- 74 0 IN IP4 10.229.0.58
s=session
c=IN IP4 10.229.0.58
b=CT:17
t=0 0
m=audio 59806 RTP/AVP 8 0 3 97 101
k=base64:P6l1kBQy3canYTWZkxccjAVtTWO9g/N5L4gxLtX0UnM
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:3 GSM/8000
a=rtpmap:97 RED/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=encryption:optional

Console output once it rings and after I answer on the PSTN side:

v=0
o=FreeSWITCH 1227887572 1227887573 IN IP4 10.229.0.10
s=FreeSWITCH
c=IN IP4 10.229.0.10
t=0 0
a=sendrecv
m=audio 30896 RTP/AVP 3 101 13
a=rtpmap:3 GSM/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=rtpmap:13 CN/8000
a=ptime:20

When I receive a call from the SIP gateway, the endpoint making the call
(not on freeswitch) can't hear me speaking from the GSM device connected to
freeswitch.  I can hear everything fine on the GSM device.

Here is the console output for the call info coming in from the PSTN.

v=0
o=FreeSWITCH 1227902084 1227902085 IN IP4 38.113.164.132
s=FreeSWITCH
c=IN IP4 38.113.164.132
t=0 0
a=sendrecv
m=audio 16724 RTP/AVP 0 101 13
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=rtpmap:13 CN/8000
a=ptime:20

Here is how I have vars.xml configured:

<X-PRE-PROCESS cmd="set" data="global_codec_prefs=GSM"/>
<X-PRE-PROCESS cmd="set" data="outbound_codec_prefs=PCMU,PCMA,GSM"/>


When I prioritize GSM on the outbound codec prefs I get static on the PSTN
side. 

<X-PRE-PROCESS cmd="set" data="outbound_codec_prefs=GSM,PCMU,PCMA "/>

Any ideas?

Maxim.