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#243230 2-Dec-2018 11:16
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Apologies if this has been covered before.


About 5 months ago we were switched from POTS to VOIP landline.  I 'knew' at the time that our alarm monitoring would cease to work but was too busy at the time to get the issue sorted.  It is an old Paradox system (at least 14 years old). We did have some minor components upgraded 6 years ago when we moved here but it is still quite limited in its capabilities.


As it happened, for the first two months our VOIP landline was effectively unusable (other thread). I suspected the problem may have been caused by the old alarm system still trying to dial out each day.  That turned out not to be the case.  The problem was at the Vodafone VOIP server end.  But to eliminate the alarm as a possibility, I cut the old house internal phone wiring off at the point where it enters the master splitter.  I contacted the monitoring company a couple of times about getting our alarm control panel replaced but never got them to respond with an actual quote. Lack of time, plus the thought of the likely cost(!), meant I still have not followed up further so assumed we have been paying the monthly alarm monitoring fee effectively for nothing for the last 5 months; ie. alarm not actually being monitored.


Late (frown) last night when checking our landline usage, I discovered our landline had been making up to 7 calls a day to a local number I didn't recognise - each call exactly 15 seconds long.  These started mid-October.  I initially thought one of our computers must have been hacked. Given that our old internal wiring link to the outside world had been physically cut, it did not seem plausible that the calls were coming from the alarm system. 


However, on discussing with one of my sons, he reminded me that ~1.5 months ago he had shifted the landline base station to a location more remote from our modem.  Rather than having the base station directly plugged into the modem, he ran a short cable from the modem to the old VDSL jack nearby, then plugged the base station into one of the old phone jacks elsewhere in the house.  Was a bit of a pot shot but the landline worked fine and has ever since.  A lot neater than loose wires on the floor (concrete block walls, concrete slab floor, no roof space so near impossible to add internal wiring without extensively cutting into walls etc).


Turns out that action also re-connected the old alarm system to the outside world, except instead of directly connecting to the incoming wire, it is now re-routed through the phone jack on the back of the modem. 


I had always 'understood' that the old alarm system was incompatible with VOIP and needed to be replaced by a modern digital version.  But (at a more civilized hour) this morning I have confirmed with the alarm monitoring company that the number being dialed is their local dial-in number, AND that our monitoring has been fully functional since mid-October. Their logs show both the daily test call, and alarm setting/un-setting calls coming through correctly.


Perhaps I missed something, but I don't recall seeing anywhere that old alarm systems can (will?) work over VOIP.  Just a matter of connecting through the modem rather than directly to the outside line. 


All three companies I spoke to regarding a new base station recommended solutions using mobile wireless connections. None indicated that they had solutions that worked over VOIP, let alone mention that all we needed to do was to connect the line from the alarm through the phone jack on the back of the modem.  Now glad I didn't get the system replaced.  Saved a hefty chunk of cash.

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  #2138097 2-Dec-2018 12:56
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Can alarms work over VoIP? Yes they can - as you've discovered. There are multiple  reasons alarms fail so it's not a one size fits all answer.


Most alarms use ContactID which sends fast DTMF tones as the signalling. Some use low speed (typically 14.4k) data modulation using QAM.


In the VoIP world most DTMF is carried out of band using RFC2833/RFC4733, so the DTMF tones are decoded at the ATA, carried across the SIP call as signalling and then ultimately converted back to inband DTMF tones at some point. It's done for this reason because DTMF can't be used inband if at any point the call is transcoded (or uses) an uncompressed codecs such as G.729 as the DTMF tones will be garbled. The main issue is that hardware struggles to decode these tones due to the speed of them.


If the VoIP provider is using inband DTMF rather than RFC2833/RFC4733 then things can work perfectly - until you end up with jitter or even minimal packet loss where things will simply break.


If you have a modem using low speed data rather than ContactID this can also work if the provider us using alaw or ulaw for the codec.


The problem is that while thing can work, they can also break. An alarm is typically the sort of thing you want 100% reliability from, not 99.9%, so the best option is either IP adapters or over 3G/4G







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  #2138120 2-Dec-2018 14:00
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As steve said, it will mostly work until it doesnt. No alarm "monitoring" company will sell a service based on that level or performance.


Also the move to a cellular connection gets you actual monitoring being a possibility with some suppliers, rather than the crude set/unset/checkin occasional crap that passes for a PSTN monitored alarm.


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