[Freeswitch-users] How to inspect the jitterbuffer?

John freeswitch at earthspike.net
Sat Feb 11 02:38:27 MSK 2012

Holger, Anthony,

I'm seeing a similar/identical 'feature' where the voice is 
intermittently broken on ISDN; I've raised ticket #1310 with Sangoma.  
My MTU is still on the default 80 but there is no IDLE_FLAG setting 
(default 0, I guess?).

Interestingly(!), it is intermittent and unpredictable, but when it 
manifests there is no clear pattern as to what will be disrupted; A wav 
audio played by a Lua IVR will be fine, then on the same call the MOH 
will be broken, as will the voicemail outgoing message and finally the 
internal user's speech.  The path from ISDN into FreeSWITCH is never 
disrupted (no surprise).  Record_session doesn't show the breaks and 
there's nothing in the FS logs.  I have sample audio taken from another 
(SIP only) FreeSWITCH instance which demonstrates the problem, but as 
the fault is intermittent and on a production system, debugging is 
taking some time.  Sangoma has asked me to take samples at the ISDN (S?) 
interface and the echo canceller on the B700 board.  When I next have 
the problem manifest, and grab those traces, I should be able to share 
the results once Sangoma has decoded them.  I can make available the 
audio samples I already have if that would help.

On 10/02/12 21:24, Anthony Minessale wrote:
> That made no sense in regards to my last message.
> I asked you to try particular wanpipe parameters, so you should try
> them and restart your wanpipe and report the results.
> Your MTU is very high and may cause timing issues for interop with voip.
> set MTU to 80 (10ms)
> set IDLE_FLAG to 0xFF (send the 255 byte on idle stream)
> 1) Turn off FreeSWITCH
> 2) wanrouter stop
> 3) wanrouter start
> 4) start FreeSWITCH
> You are pushing RTP up against TDM, RTP can start and stop, TDM
> cannot, When there is no RTP the TDM will carry on sending the
> IDLE_FLAG byte over the wire.
> I made both the RTP stack and the TDM endpoint from scratch so you
> should assume I may have some insight.
> On Fri, Feb 10, 2012 at 12:28 PM, Holger Freyther<holger at freyther.de>  wrote:
>> Anthony Minessale<anthony.minessale at ...>  writes:
>>> If there is no RTP then the TDM should be generating its own audio.
>>> Try
>>> MTU           = 80
>>> IDLE_FLAG     = 0xFF
>> Writing about audio is difficult. Imagine one says the word "Two"..
>> and one called a mailbox. Opening the file in audacity gives you
>> the wave of what you said, you zoom in and you see that in the
>> middle of the word the the amplitude is zero for a bit (where it
>> should not be zero). As echoing works on FreeTDM, there is no packet
>> loss in RTP, the bug has the whole audio... it means something is
>> broken in FreeSWITCH to get the audio to FreeTDM in time?
>> Any ideas?

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