[asterisk-bugs] [DAHDI-linux 0017318]: FXS Polarity Reversal on Hangup

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=17318 
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Reported By:                armeniki
Assigned To:                
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Project:                    DAHDI-linux
Issue ID:                   17318
Category:                   NewFeature
Reproducibility:            always
Severity:                   major
Priority:                   normal
Status:                     new
JIRA:                        
Reviewboard Link:            
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Date Submitted:             2010-05-11 06:12 CDT
Last Modified:              2010-05-11 22:42 CDT
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Summary:                    FXS Polarity Reversal on Hangup
Description: 
FXS lines normally connect to a telephone.  However, when FXS lines are
routed to an external PBX or Key System to act as "external" or "CO" lines,
it is extremely difficult, if not impossible for the external PBX to know
when the call has been disconnected without receiving a polarity reversal
on the line.

DAHDI/Asterisk should have a feature to allow a setting someplace, perhaps
in chan_dahdi.conf, to allow a FXS channel to provide a polarity reversal
on channel hangup.
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 (0121763) armeniki (reporter) - 2010-05-11 22:42
 https://issues.asterisk.org/view.php?id=17318#c121763 
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Hi Alec,

The behaviour of a CO line with Line Reversal, is as follows.  Note that
the phone company offers this service in two different flavours, one is
called ROA (reverse on answer) and the other is ROD (reverse on
disconnect).  You can also choose to have both if you needed but that's
rare. It's basically a manner of what event causes the reversal.

In the case of this particular ticket, ROD (reverse on disconnect) would
be the feature.

ROD works likes this:
1) Telephone is Onhook - polarity FWD
2) Telephone goes Offhook - polarity FWD
3) User dials number - polarity FWD
4) Call is answered - polarity FWD
5) Call is disconnected - polarity **REV**
6) Telephone goes back Onhook - polarity resets back to FWD

ROA (reverse on answer) works in the same manner except polarity changes
on ANSWER instead of HANGUP, like this:

1) Telephone is Onhook - polarity FWD
2) Telephone is Offhook - polarity FWD
3) User dials number - polarity FWD
4) Call is answered - polarity **REV**
5) Call is disconnected - polarity FWD
6) Telephone goes back Onhook - polarity resets back to FWD

The important thing to note is that for any of these scenarios, the
polarity never changes if the call is not completed (answered or hangup). 
So if the number dialed is BUSY, etc. it will not change.

Cheers,
Armen 

Issue History 
Date Modified    Username       Field                    Change               
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2010-05-11 22:42 armeniki       Note Added: 0121763                          
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