[asterisk-users] OT - Do analog gateways detect a phone is plugged in or out ?

[Lyle Giese]

Philipp Kempgen wrote:
> Steve Totaro schrieb:
>   
>> On Wed, Jul 22, 2009 at 12:07 PM, Steve Underwood <steveu at coppice.org>wrote:
>>     
>>> Olivier wrote:
>>>       
>>>> I've got a general question about analog gateways (Xorcom, Audiocodes,
>>>> Patton, ...) .
>>>> Is it usual for analog gateways to detect when an analog phone is
>>>> plugged in or out ?
>>>> If positive, would it be then useful to send "qualify" queries for
>>>> each connect phone (I'm implying here that an analog gateway would
>>>> then reply appropriately for qualify query.
>>>>         
>>> Unless there is a call in progress the switch has no idea what phones
>>> might be plugged or unplugged. Nothing happens on the line what it could
>>> detect.
>>>       
>
>   
>> It certainly would seem "possible" and would be a great feature request.
>>
>> There probably is no circuitry existing to do it, but I would assume that
>> ohms, volts, or something could be measured while sending a small amount of
>> voltage down the FXS lines.
>>     
>
> Bonus point will be given for detecting the phone model and color
> as well. ;-)
>
>
>     Philipp Kempgen
>   
Yes, it's technically possible for the phone company to determine if
there is a set or something connected to a phone line.  It involved
hitting the line with +130v dc test voltage and reversing it quickly and
seeing how much capacatance kick there is.  This kind of testing is
normal for telco CO lines. 

FXS chan units or gateways normally do NOT have this built into them. 
The only exception I know about is SLC(Subscriber Line Concentrator,
which is a generiac term for fiber or digital lines feed to telco boxes
in the field).  And even there the process was to have a cut-in relay
and connect the out cable pair back to the CO via a dedicated copper
pair to do these tests via a device called a PairGain Test Controller. 
I know because I was an 'expert' on them and traveled around going from
telco CO to CO fixing them.

In other words, there is some circuitry involved in doing these tests
and I don't see any PBX, FXS chan unit or gateway manufacturer rushing
to add more to this to their product line.  They have not done it yet
and I don't see anyone other than the phone company willing to spend the
money to make it happen.

To keep this on topic for Philipp's remark, the only bonus points we
assigned was to correctly guess how many phones were attached to the
phone line<GRIN>!

Lyle Giese
LCR Computer Services, Inc.

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