[Freeswitch-users] Codec negotiation questions

Fri Feb 13 06:57:48 PST 2009

Hi Anthony,

Excuse me if I'm wrong but inbound-late-negotiation must be used proxy_media
as I see in documentation. I don't want to proxy media because of some
issues with MOH or 3-way conferencing. Also I want to exclude media codecs
that are supported only in pass-trough mode. Let mi give you an example:

SDP from caller

   v=0
   o=- 1 2 IN IP4 192.168.20.193
   s=CounterPath eyeBeam 1.5
   c=IN IP4 192.168.40.81
   t=0 0
   m=audio 56888 RTP/AVP 100 106 97 105 98 3 101
   a=fmtp:101 0-15
   a=rtpmap:100 SPEEX/16000
   a=rtpmap:106 SPEEX-FEC/16000
   a=rtpmap:97 SPEEX/8000
   a=rtpmap:105 SPEEX-FEC/8000
   a=rtpmap:98 iLBC/8000
   a=rtpmap:101 telephone-event/8000
   a=sendrecv
   a=x-rtp-session-id:61940567309B49E8909127E1393A966E
   m=video 46378 RTP/AVP 125 115 34
   a=fmtp:125 profile-level-id=42e015; max-br=4000; max-mbps=19800
   a=fmtp:115 QCIF=1 MAXBR=4520
   a=fmtp:34 QCIF=1 MAXBR=4520
   a=rtpmap:125 H264/90000
   a=rtpmap:115 H263-1998/90000
   a=rtpmap:34 H263/90000
   a=sendrecv
   a=x-rtp-session-id:E8244E608F65445BA183BBE641C5DF3C
   a=nortpproxy:yes

SDP from Freeswitch to called

   v=0
   o=FreeSWITCH 6228154995644782318 4633980766357417433 IN IP4 10.10.10.10
   s=FreeSWITCH
   c=IN IP4 10.10.10.10
   t=0 0
   m=audio 26920 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

So we offer *only first* in codec preference list

from called wich is normal receives
   SIP/2.0 488 Not Acceptable Here
*called suports - PCMA,PCMU,iLBC
*
Codec preference to this vars.xml we have witch is used in provile:
<X-PRE-PROCESS cmd="set" data="all_codec_prefs=GSM,speex at 32000h
@20i,speex at 16000h@20i,speex at 8000h@20i,*iLBC at 30i,PCMA,PCMU*,G729"/>
also we have in profile:
<param name="inbound-codec-negotiation" value="greedy"/>
<param name="disable-transcoding" value="true"/>
In dialplan I've set:
<action application="set" data="inbound-late-negotiation"/>
<action application="set" data="inherit_codec=true"/>

About my second question:
Why I should parse variable_switch_r_sdp: [v=0
o=- 6 2 IN IP4 192.168.20.193
s=CounterPath eyeBeam 1.5
c=IN IP4 192.168.40.81
t=0 0
m=audio 60642 RTP/AVP 100 106 97 105 98 3 101
a=rtpmap:100 SPEEX/16000
a=rtpmap:106 SPEEX-FEC/16000
a=rtpmap:97 SPEEX/8000
a=rtpmap:105 SPEEX-FEC/8000
a=rtpmap:98 iLBC/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=x-rtp-session-id:0674790128EB43ACB8C7F55829BCFF14
m=video 44938 RTP/AVP 125 115 34
a=rtpmap:125 H264/90000
a=fmtp:125 profile-level-id=42e015; max-br=4000; max-mbps=19800
a=rtpmap:115 H263-1998/90000
a=fmtp:115 QCIF=1 MAXBR=4520
a=rtpmap:34 H263/90000
a=fmtp:34 QCIF=1 MAXBR=4520
a=x-rtp-session-id:D1EAE543055746AC9C03006B91ADE6DF
a=nortpproxy:yes
]
In FS core this parse is already done I'm sure in much more intelligent way.
It can be exported as a variable like a absolute codec string I think.

Thanks again.

2009/2/12 Anthony Minessale <anthony.minessale at gmail.com>

> the entire sdp is available as a variable (route the call to the info app
> to see the variables)
> so if you have inbound-late-negotiation set to true on the sip profile
> then you can use a regex or a script to set absolute_codec string before
> you answer.
>
>
> On Thu, Feb 12, 2009 at 8:06 AM, ivdreg ivdreg <ivdreg at gmail.com> wrote:
>
>> Hi all,
>>
>> Can I ask 2 questions about codec negotiation:
>>
>> 1. Is it possible Freeswitch to work negotiate codecs between two phones
>> as it is described below.
>> INVITE from A with some codecs in SDP ---> Freeswitch rewrites codec
>> preference according absolute_codec_string but exclude all codecs not
>> offered by A ----> INVITE to B with rewrited SDP.
>>
>> example:
>> from A SDP:PCMA,PCMU,SPEEX  ----> absolute_codec_string=G722,PCMU,PCMA,GSM
>> ----> to B SDP: PCMU,PCMA
>>
>> 2. Can I get codec list in INVITE with mod_perl for example or via
>> xml_curl without processing SDP variable (switch_r_sdp). It will be useful
>> to be in format that absolute_codec_string variable takes.
>>
>> Thanks
>>
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>>
>
>
> --
> Anthony Minessale II
>
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