[Asterisk-Users] RE: Caller ID

[Greg Blakely]

I've come late into this thread, so I risk saying things that you all
will just shake your heads at and say, "Duh!"

Historically, though, from WAY back in the days of electromechanical
switches, reverse battery mainly provided answer supervision.  Its
usefulness pretty much went away with the advent of SS7, except for
those cases where end users resold their POTS services (such as hotels
and motels, which usually paid extra for the service).

The battery would then reverse BACK to normal again after the call was
terminated.  During this reversal (obviously), the voltage would
transition past zero, and it would also suffice for disconnect
supervision.

Aside from the hotel/motel scenario, telcos have recently been providing
disconnect supervision solely by means of removal of battery from the
circuit.  This feature continues to be of value in situations where
analog CPE would continue to keep the line seized were it not for the
removal of the battery -- key systems having lines on hold, answering
machines, etc.

Personally, I would very much like to see the reverse battery feature
built in to the FXS cards that work on asterisk.  I say this because I
am starting to go back to my roots in the industry by looking for old
step-by-step line finders, selectors, and connectors.  Answer
supervision via some electromechanical means would be preferable than
trying to cobble an ISDN D channel over to that old stuff.

Just my 2 cents.


> -----Original Message-----
> From: asterisk-users-admin at lists.digium.com 
> [mailto:asterisk-users-admin at lists.digium.com] On Behalf Of 
> Kevin Walsh
> Sent: Sunday, May 02, 2004 1:05 PM
> To: asterisk-users at lists.digium.com
> Subject: RE: [Asterisk-Users] RE: Caller ID
> 
> Steve Underwood [steveu at coppice.org] wrote:
> > Wake up.
> >
> Sorry, I must have drifted off for a while.  Thanks for the 
> alarm call.
> 
> > 
> > The reversal detection is a complete waste of time. Totally 
> unnecessary.
> > Pointless. A line break detector would have much more use, 
> as it would 
> > give a reliable disconnect detection on many lines. (Actually, 
> > reversal detection would have years ago, but its not much 
> use any more).
> >
> Perhaps both would be good then:  A polarity reversal 
> detector for determining the start of a Caller*ID sequence 
> and a line break detector for, err, detecting line breaks.  
> Actually, my X101P seems to detect hangups just fine, so I've 
> not had cause to check whether the detection is done in the 
> hardware or in the driver.  If you say that it's not done in 
> hardware then I'll take your word for it for the moment.
> 
> > 
> > All you need for these CLI requirements is to monitor for 
> some energy 
> > on the line. Since these FXOs are not being used in banks 
> of hundreds, 
> > you will never notice this MIPs this uses.
> > 
> I'd still prefer to see this done in hardware, rather than in 
> some sort of idle loop in the driver or the application.  
> Call me old fashioned, but I prefer it when unnecessary 
> overheads are not measured in MIPs. :-)
> 
> Perhaps the new FXO module for the TDMxxB has, or will have, 
> hardware support for the above.  If it has, and I'm sure I 
> heard somewhere that it does, then that's great.  An X102P, 
> with similar support, would no doubt be welcome too.
> 
> -- 
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>  _/ _/    _/          _/ _/     _/    _/  _/_/    kevin at cursor.biz
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