[asterisk-bugs] [Asterisk 0016936]: [patch] Qualify frequency has big pauses. Asterisk stops sending SIP OPTIONS to keep NAT alive

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=16936 
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Reported By:                ib2
Assigned To:                
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Project:                    Asterisk
Issue ID:                   16936
Category:                   Channels/chan_sip/General
Reproducibility:            sometimes
Severity:                   major
Priority:                   normal
Status:                     acknowledged
Asterisk Version:           1.6.2.4 
JIRA:                       SWP-993 
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:             2010-03-01 13:54 CST
Last Modified:              2010-04-30 11:04 CDT
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Summary:                    [patch] Qualify frequency has big pauses. Asterisk
stops sending SIP OPTIONS to keep NAT alive
Description: 
We have several SIP phone peers that that becomes UNREACHABLE since
upgrading to Asterisk 1.6.2.x

[10:08:44] chan_sip.c: Peer '202_117' is now UNREACHABLE!  Last qualify:
100
[10:11:25] chan_sip.c: Peer '202_117' is now Reachable. (86ms / 2000ms)
[11:59:03] chan_sip.c: Peer '202_117' is now UNREACHABLE!  Last qualify:
91
[12:11:27] chan_sip.c: Peer '202_117' is now Reachable. (85ms / 2000ms)
[13:17:21] chan_sip.c: Peer '202_117' is now UNREACHABLE!  Last qualify:
90
[13:41:27] chan_sip.c: Peer '202_117' is now Reachable. (92ms / 2000ms)

The phone is UNREACHABLE until it registers again. The phone does not know
that it is UNREACHABLE.
Asterisk reports the phone as UNREACHABLE after a big pause in sending SIP
OPTIONS to keep NAT alive. Therefore NAT table is lost and asterisk cannot
receive SIP OK reply from the phone.

The typical interval between the occurrence is shown above
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 (0121229) cappucinoking (reporter) - 2010-04-30 11:04
 https://issues.asterisk.org/view.php?id=16936#c121229 
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I'm seeing the exact same behaviour, but with two asterisk machines talking
to each other using SIP. Both are non-NAT however.

Only seems to happen when other calls are going through the system, rarely
happens over night.

Can't see anything in core show locks around the times when this is
happening.
But since it is pretty random when it is happening, it is very difficult
to catch at the right time.