[asterisk-bugs] [Asterisk 0016010]: Call abort after wrong behaviour of VNAK transmission

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=16010 
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Reported By:                ffloimair
Assigned To:                
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Project:                    Asterisk
Issue ID:                   16010
Category:                   Channels/chan_iax2
Reproducibility:            sometimes
Severity:                   major
Priority:                   normal
Status:                     acknowledged
Asterisk Version:           1.4.26.2 
JIRA:                        
Regression:                 No 
Reviewboard Link:            
SVN Branch (only for SVN checkouts, not tarball releases): N/A 
SVN Revision (number only!):  
Request Review:              
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Date Submitted:             2009-10-02 03:22 CDT
Last Modified:              2009-10-28 05:16 CDT
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Summary:                    Call abort after wrong behaviour of VNAK
transmission
Description: 
Asterisk sends VNAK to signal a retransmission of a packet. After
retransmission the request is sent again and again... Abort of the call is
the result after a few retries.
Overall, asterisk very often sends VNAK after receiving LAGRQ and PING
consecutively. Why does asterisk know that packet 2 after 1 is missing if
there was no packet 3 so far (numbers referring to ascending sequence
numbers in IAX Header)? This is confusing since the RFC states the below
text requiring to retransmit all frames with a higher sequence number than
the one received with the VNAK.

Please see the attached pcap file.

There was no significant output in the asterisk console, so I do not post
this as of now. If required I can post this later.

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Relationships       ID      Summary
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duplicate of        0016055 Loss of IAX calls after strange VNAK be...
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 (0112836) dreamer2000 (reporter) - 2009-10-28 05:16
 https://issues.asterisk.org/view.php?id=16010#c112836 
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I looked through the pcap file and i think i have 2 ideas for possible
reasons why the calls are dropped after "max tries exceeded...":

1.
one part sends PING (SEQ-ID) and LAGRQ (SEQ-ID+1), after this asterisk
answers with VNAK (SEQ-ID) which looks like a bug at all because of
IAX2-RFC: 6.9.3. VNAK: Voice Negative Acknowledgement Message - you must
repeat frames with a higher seq-id as in VNAK - in case that PING is lost,
the VNAK should say SEQ-ID-1! PING must be the frame that is lost because
otherwise asterisk would not know that one frame is lost after there is no
third packet.
2.
after receiving 2 frames in a row in a very small time slot it seams that
maybe the receiving queue is read out wrong. I do not know how this is
handled - is it FIFO ? or is the queue handled via iax-timestamps? in this
case the two frames have the same timestamp and may be mixed up all the
time until time out error.. 

Issue History 
Date Modified    Username       Field                    Change               
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2009-10-28 05:16 dreamer2000    Note Added: 0112836                          
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