[Asterisk-Dev] Ring requested on channel already in use

[alan]

A problem was recently posted on the Asterisk-Users mailing list, and it
went unresolved. Now that it's plaguing our production system as well, I
need to look into it further.

I am fairly sure this is a bug and not a misconfiguration issue. I will
be happy to provide much more additional information, after I'm sure
it's a bug and not a -users issue :)

Summary:

Occasionally, the same PRI channel receives two "Channel ... got hangup"
notifications in sequence, with no intervening activity on the channel.
A subsequent call coming in to the same span and channel receives the
"warning:"
Ring requested on channel 0/3 already in use on span 1. Hanging up owner.

When this happens, Asterisk enters an inconsistent state, which I have
only been able to correct by restarting.

Some symptoms I've seen when it's in this state are: previously active
"asterisk -r" sessions fail to exectue commands; most/all extensions
fail when dialed by local phones; and of course incoming calls on the
PRI fail (with the Ring Requested error).

A few more details:

I dug into chan_zap.c, and found 2 places which generate the exact same
"Channel 0/3, span 1 got hangup" message, both in the huge function
pri_dchannel. One was inside "case PRI_EVENT_HANGUP" and one was inside
"case PRI_EVENT_HANGUP_REQ".

I recompiled with slightly different error messages, so I could see what
was happening in this case. In the one failure case I've had since that
change, the first "Channel got hangup" message was generated by the
PRI_EVENT_HANGUP_REQ case, and the second message was generated by
PRI_EVENT_HANGUP.

"set debug 4" and "pri intense debug" logs are available if anyone knows
more about parsing the intense PRI debugging than I do.


** System specs:
Asterisk 1.0.8
libpri 1.0.8
zaptel 1.0.8
fedora core 3
1x Digium Wildcard TE110P, single T1/E1 card
  with a T1/PRI to the PSTN (US)


The previous problem description in Asterisk-Users:
http://lists.digium.com/pipermail/asterisk-users/2005-July/117242.html

A note on voip-info.org acknowledging the issue and providing a
completely inadequate hack for it:
http://www.voip-info.org/tiki-index.php?page=Ring+requested+on+channel


Thank you very much for any help you can give me in tracking down
this problem.

Alan Ferrency
pair Networks, Inc.