[Asterisk-Users] Excessive VNAK's and jitter over IAX2

[Matt Lawson]

Howdy,

I recently saw something strange with a call between  *'s over IAX2. 
 There are actually 3 *'s involved.  The setup is like this:

SIP phone ------(ulaw over LAN)------ *1 -------- IAX2 (ulaw over 
Internet) ---------*2--------(GSM over Internet) 
-----------*3--------(ulaw over LAN)------ SIP phone

Now what is shown below is the Asterisk in the middle, that is doing the 
conversion between the other two, one of which only speaks ulaw and the 
other only speaks GSM.

The call basically seemed to work, except the audio quality was 
terrible, but it did seem to be basically connected.  Asterisk started 
spewing out these VNAK messages, thousands of them as fast as it could. 
 In the middle of it I did an "IAX2 show channels" to show what was in 
progress.

The asterisk version shown here is a completely stock, CVS version from 
just a few days ago.  The "outboard" Asterisks are somewhat modified but 
also re-synchronized with CVS within the last week.

Also, all Asterisks have iax jitterbuffer=no.

So, my questions are:

1.  What do the excessive VNAKs indicate?  Some type of communication 
error?  NAT-related perhaps?
2.  Does the 20,000+ jitter have something to do with the audio sounding 
terrible?
3.  Why is there jitter at all if all Asterisks have their IAX2 jitter 
buffers turned off?
4.  Is there any significance to the "Username (none)" for one of the 
peers?  The Asterisk has both peer and user names for both machines. 
 The caller name shows up, but the callee name is always "(None)"

Ideas anyone?  Thanks.


DEBUG[98311]: File chan_iax2.c, Line 4649 (socket_read): Sending 
VNAK                                                       
DEBUG[98311]: File chan_iax2.c, Line 4649 (socket_read): Sending 
VNAK                                                       
DEBUG[98311]: File chan_iax2.c, Line 4649 (socket_read): Sending 
VNAK                                                       
DEBUG[98311]: File chan_iax2.c, Line 4649 (socket_read): Sending VNAK
                                                        
s                                                                                                                            

Peer             Username    ID (Lo/Rem)  Seq (Tx/Rx)  Lag      Jitter  
Format                                              
24.9.xx.xxx      i58         00009/00003  00015/00006  00000ms  0169ms  
ULAW                                               
66.167.xx.xxx    (None)      00010/00004  00008/00013  00009ms  20743ms  
GSM                                                
2 active IAX 
channel(s)                                                                                                      

*CLI> DEBUG[98311]: File chan_iax2.c, Line 4649 (socket_read): Sending 
VNAK                                                 
DEBUG[98311]: File chan_iax2.c, Line 4649 (socket_read): Sending 
VNAK                                                       
DEBUG[98311]: File chan_iax2.c, Line 4649 (socket_read): Sending 
VNAK                                                       
DEBUG[98311]: File chan_iax2.c, Line 4649 (socket_read): Sending VNAK