Using SPA112 to connect an alarm system via 3CX

[TuxTiger]

My alarm system uses an analogue telephone line to send daily status reports and report fire and burglary. I have been trying to get the system to work via a Linksys SPA112 through my 3CX (linux) system.

I cannot get the system to work through 3CX. Using the trunk (same as 3CX uses) direct on the SPA112 works! So:

does work: SPA112 -> trunk
does not work: SPA112 -> 3CX -> trunk

The alarm system uses a rapid sequence of dtmf tones to communicate. I have setup the SPA112 to send dtmf in 'auto' mode and it worked immediately using the trunk on the SPA112, but also tried InBand dtmf when it did not work via the 3CX.

I hope anyone can give me some pointers?

 

[eddv123]

Hi Tuxtiger,

This is just an analogue connection from an FXS port to a ringer I guess, so it is odd you are seeing such behavior.

One point I would note is can you advise as to where the ATA is located in relation to the 3CX system (is it hosted or on premise) ? hosted is not supported as per: https://www.3cx.com/voip-gateways/patton-smartnode-sn4112-fxs/

Now I don't use Cisco kit but does the device has syslog functionality that you can output to wireshark or kiwi for example, it may give you an idea of what the issue might be.

 

[TuxTiger]

Hi eddv123,

The SPA112 is located at home. The 3CX runs on a server in a data center, so not local. On the local network a SBC is installed to connect all local SIP phone with the 3CX, also the SPA112 is instructed to use the local SBC.

I was able to record the phone call that was made from the alarm system to the central monitoring service (Stanley). The fast dtmf tones are send by the alarm system but the central monitoring service does not seam to receive them.

I am guessing that the 3CX server does not recognize the fast dtmf tones but I don't know how to research this.

 

[YiannisH_3CX]

As you can understand this is a not supported scenario so we cannot guarantee that this will work. Not only is the ATA device not in the supported list but also it is not local and it is registered through an SBC. If you can bring the device local to the PBX you can try one of the supported devices here:
https://www.3cx.com/voip-gateways/

 

[eddv123]

I do second what Yiannis has said despite the fact that I have managed to get supported (and un-supported gateways) working across the SBC (and in some cases even direct SIP/STUN) you are asking for trouble getting an un-supported device working to a hosted system - especially since (for supported devices) only VPN is recommended/supported as a connection method.

 

[CentrexJ]

While the SPA112 works great through 3CX to be used with an analog telephone or when paired with a T.38 SIP trunk for FAXING, you will be unable to use it with a modem type device (Alarm System, Debit Machine, Postage Machine, Dial-Up Modem).

Generally we recommend to people to upgrade their alarm to have either GSM/LTE based cell connection or Ethernet/Internet based connection.

If the alarm is DSC or Honeywell check this product out. Amazing cheap upgrade to make it internet capable:
https://www.aartech.ca/envisalink-evl4.html

 

[leejor]

Be sure that G711 Codecs are used if you are trying to send Inband (audio) DTMF. Low bit rate Codecs don't handle audio DTMF well, if at all. If the alarm system is trying to send Data, as a modem, you may be out of luck. What type of trunk are you using?
You may want to Wireshark a direct connection (which you say works) and one routed through 3CX to see the differences. I'm going to assume there will be something in the Invite.

 

[TuxTiger]

Thanks all!

@CentrexJ: the communication is not using modem signals but using DTMF tones, like a regular phone can do only more quickly.

@YiannisH_3CX: I thought the SBC service tunnels all VOIP traffic to the remote 3CX, why should an ATA be on the same net as 3CX? The SPA122 works perfectly through SBC -> 3CX for all calls using analogue phones connected to the SPA112. Also walking through IVR menus is working, so voice and DTMF are functional.

I will make a tcpdump capture of the traffic from the SPA112 directly to the trunk and compare it witl the 3CX traffic (coming from the SPA112) to the trunk.

I suspect the 3CX does not recognizes the (fast) DTMF tones (when not using InBand ofcourse), how can I debug if the 3CX detects those from the incoming SPA112 ?

I am coming from Asterisk and am missing the command line interface with 'core set debug' and things...

 

[cobaltit]

So someone else was trying to something similar with some Point of Sale system. I will tell you the same thing any seasoned installer will tell you, and that is to stick with what the vendor recommends. If you want the alarm system to work, use a POTS line like it expects. If you really want to get rid of the POTS line, then see if the vendor offers a cellular connection that they support.

 

[leejor]

If it works when connected directly through the SPA112, then I'd leave it at that. I don't see the point of having 3CX in-between.

Most providers will allow SIP forking, check with them. the trunk may be able to appear on both the SPA and in 3CX, as a trunk, if that is what you want. The fewer "things" between an alarm system and the location they are to contact, the better.

 

[YiannisH_3CX]

I thought the SBC service tunnels all VOIP traffic to the remote 3CX, why should an ATA be on the same net as 3CX? The SPA122 works perfectly through SBC -> 3CX for all calls using analogue phones connected to the SPA112. Also walking through IVR menus is working, so voice and DTMF are functional.

The SBC does route all traffic through the tunnel but as you can see even supported ATA devices are only supported for local use. While technically this could work this was never tested by us and we cannot guarantee the correct functionality. As mentioned try to keep things as simple as possible and especially in case of alarms always try the supported route.

 

[YiannisH_3CX]

I will make a tcpdump capture of the traffic from the SPA112 directly to the trunk and compare it witl the 3CX traffic (coming from the SPA112) to the trunk.

Please keep in mind during your testing that traffic coming through the tunnel might not be visible in wireshark as it is encapsulated.

 

[TuxTiger]

@YiannisH_3CX: thanks, the SBC machine is also linux, I will run tcpdump from there

@leejor: shortest route, of course...you are absolutely right, direct access from the ATA to the outgoing trunk is the way to go.

Thanks all!

 

[YiannisH_3CX]

Glad we could assist