[asterisk-bugs] [Asterisk 0009660]: [patch]Asterisk can't establish dialtone after brief hangup

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A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=9660 
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Reported By:                mmacvicar
Assigned To:                
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Project:                    Asterisk
Issue ID:                   9660
Category:                   Channels/chan_zap
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     ready for testing
Asterisk Version:           1.4.4 
SVN Branch (only for SVN checkouts, not tarball releases): N/A  
SVN Revision (number only!):  
Disclaimer on File?:        No 
Request Review:              
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Date Submitted:             05-03-2007 14:08 CDT
Last Modified:              11-08-2007 02:24 CST
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Summary:                    [patch]Asterisk can't establish dialtone after brief
hangup
Description: 
Asterisk can't establish dialtone after brief hangup

When I press the hook-switch (i.e., receiver button) and then let go to
make a new call, the phone doesn't establish dialtone unless I hold it down
for for 4-5 seconds.

Reproducible Steps:
1. Pick up handset and establish dialtone.
2. Press the hook-switch for 1-3 seconds and let go

After letting go of the hookswitch, the sound on the line is silent for a
moment then a computerized squeal is heard briefly and silence continues.
The asterisk console displays the following messages when "core set verbose
10":
--------------------
    -- Starting simple switch on 'Zap/7-1'
    -- Hungup 'Zap/7-1'
[May  3 11:31:45] WARNING[2241]: chan_zap.c:1616 zt_set_hook: zt hook
failed: Device or resource busy
--------------------

We are using analog Astra Telecom 480e phones connected through internal
wiring to TDM400P cards in our asterisk server.


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====================================================================== 

---------------------------------------------------------------------- 
 meneault - 11-08-07 02:24  
---------------------------------------------------------------------- 
jmhunter:
Basically loopstart signalling and kewlstart signalling are almost the
same.
Choosing one or another is usually a question of hardware i.e your phones
for FXS channels. 

kewlstart is an add-on of loopstart, with loopstart you can't know when
other party has hanged up, you are obliged to detect a congestion tone and
then hangup. Usually on your asterisk configuration for your FXO channels
you would have something like busydetect=yes (or call progress detection or
hangup on polarity switch).

With kewlstart signalling on an FXO channel, the telco provider drop the
battery when other party has hanged up, thus your asterisk automatically
knows that the conversation is over and can hangup the channel
automatically, without trying to detect the congestion tone.
So for FXO channels the difference is really important.

For FXS channels it does not really matter to know when the communication
is over because on FXS channels you usually connect regular phones which
are taken off-hook by humans (i.e not computers). And when the channel is
hanged up asterisk plays a congestion tone on the channel, thus you know
that the communication is over and you hang-up.
In kewlstart mode, asterisk (actually zaptel) also drops the battery when
the communication is over and your phones may detect this and hang-up
automatically.
So for FXS channels it doesn't hurt as much as for FXO channels and
loopstart could be a good choice if you don't need the automatic hangup
detection by your phones.

FYI, in zaptel the kewlstart handling is buggy (IMHO) because when your
phones are already on-hook zaptel indicates hangup anyway by dropping
battery during 800ms which is simply non-sense because nobody is listening
on the channel.
So my patch only remove the battery drop when nobody is listening, that
avoid you to wait 800ms before taking the phone off-hook again. 

Issue History 
Date Modified   Username       Field                    Change               
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11-08-07 02:24  meneault       Note Added: 0073367                          
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