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

[Steve Underwood]

Lyle Giese wrote:
> 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>!
Sane people just make a call, and see if the darned thing works. :-)

Steve