Philipp Kempgen wrote: > Steve Totaro schrieb: > >> On Wed, Jul 22, 2009 at 12:07 PM, Steve Underwood <[email protected]>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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