[Freeswitch-users] PCMU fallback for T.38

[Brian West]

Are you on SVN trunk 12694?

/b

On Mar 20, 2009, at 4:28 PM, Gabriel Kuri wrote:

> hey folks, I'm trying to configure PCMU fallback for T.38.
>
> The originating endpoint (Linksys SPA-2102) sends an INVITE to FS with
> G729 and PCMU in the sdp. the INVITE to the provider includes G729 and
> PCMU as part of the sdp as well (absolute_codec_string=G729,PCMU) ...
>
> m=audio 16458 RTP/AVP 18 0 100 101
> a=rtpmap:18 G729/8000
> a=rtpmap:0 PCMU/8000
> a=rtpmap:100 NSE/8000
> a=fmtp:100 192-193
> a=rtpmap:101 telephone-event/8000
> a=fmtp:101 0-15
> a=ptime:20
>
> once the FAX tone is detected on the PSTN side, FS receives a T.38
> re-INVITE from the provider and FS sends back a 488/Not Acceptable
> (proxy_media=false). at that point the provider than attempts fallback
> to PCMU with another reINVITE ...
>
> m=audio 16816 RTP/AVP 0 101
> a=rtpmap:0 PCMU/8000
> a=rtpmap:101 telephone-event/8000
> a=fmtp:101 0-15
> a=ptime:20
>
> immediately after the PCMU reINVITE, FS closes the channel and the  
> text
> below is in the FS logs. given the SPA-2102 included PCMU in the
> original INVITE, even though it was the second preferred codec,
> shouldn't FS fallback to using PCMU if it was re-INVITEd with PCMU by
> the provider? It seems like it's not passing the PCMU Re-INVITE back  
> to
> the endpoint (SPA-2102), since it originally negotiated G729 with the
> SPA2102 as that was the 1st codec in the sdp, but trying to transcode
> between the two (G729 and PCMU)?
>
>
> 2009-03-20 01:19:58 [DEBUG] sofia_glue.c:2407  
> sofia_glue_negotiate_sdp()
> Audio Codec Compare [PCMU:0:8000]/[G729:18:8000]
> 2009-03-20 01:19:58 [DEBUG] sofia_glue.c:2371  
> sofia_glue_negotiate_sdp()
> Set 2833 dtmf payload to 101
> 2009-03-20 01:19:58 [DEBUG] sofia_glue.c:2407  
> sofia_glue_negotiate_sdp()
> Audio Codec Compare [telephone-event:101:8000]/[G729:18:8000]
> 2009-03-20 01:19:58 [DEBUG] sofia_glue.c:2407  
> sofia_glue_negotiate_sdp()
> Audio Codec Compare [PCMU:0:8000]/[PCMU:0:8000]
> 2009-03-20 01:19:58 [DEBUG] sofia_glue.c:1550
> sofia_glue_tech_set_codec() Changing Codec from G729 to PCMU
> 2009-03-20 01:19:58 [DEBUG] sofia_glue.c:1601
> sofia_glue_tech_set_codec() Set Codec
> sofia/cedarwireless.net/1XXXXXXXXXX at 1.1.1.1 PCMU/8000 20 ms 160  
> samples
> 2009-03-20 01:19:58 [DEBUG] sofia_glue.c:1811  
> sofia_glue_activate_rtp()
> Audio params are unchanged for sofia/cedarwireless.net/1XXXXXXXXXX at 1.1.1.1 
> .
> 2009-03-20 01:19:58 [DEBUG] sofia.c:2896 sofia_handle_sip_i_state()
> Processing Reinvite
> 2009-03-20 01:19:58 [DEBUG] sofia.c:2542 sofia_handle_sip_i_state()
> Channel sofia/cedarwireless.net/1XXXXXXXXXX at 1.1.1.1 entering state
> [completed]
> 2009-03-20 01:19:58 [DEBUG] switch_core_io.c:655
> switch_core_session_write_frame()
> sofia/cedarwireless.net/1XXXXXXXXXX at 1.1.1.1 receive message
> [SWITCH_MESSAGE_INDICATE_TRANSCODING_NECESSARY]
> 2009-03-20 01:19:58 [ERR] mod_g729.c:145 switch_g729_decode() This  
> codec
> is only usable in passthrough mode!
> 2009-03-20 01:19:58 [ERR] switch_core_io.c:723
> switch_core_session_write_frame() Codec G.729 decoder error!
>
>
> Thanks,
>
> Gabe
>
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