[VoiceOps] Alarm panels and how they dial DTMF digits - pots migration from DMS to Metaswitch issue

[Matthew Yaklin]

On 2/13/23 11:15, Matthew Yaklin via VoiceOps wrote:
> Hello All,
> 
> I guess I have an old school question for the list. The question is we are having trouble with alarm panels dialing and our gear collecting the DTMF digits properly. Only from a company ran by a single alarm panel guy who is not terribly helpful. At least 7 different sites are having the same problem on different copper pairs/T1s. Different gear. Etc...

Is the issue that the alarm panels can't complete a call to the central monitor, or do they ring in OK and then cant pass DTMF inband once connected to communicate the nature of the alarm?


--- The issue is that when the alarm panel dials the INVITE from the TA5k does not contain the correct digits dialed. A couple of digits are missing for example. Sometimes a call does manage to squeak through properly. If the digits do get to the Metaswitch properly the call completes fine. Same exact symptom with GR303. In SAS (meta's service assurance server that contains debug output) I can clearly review what digits reach the metaswitch via GR303. In this case I will see missing digits as I know the number the alarm panel is supposed to dial and a gap of time which should have contained digits.

--- So this is not an INBAND issue when the call is active or a SIP issue. It is truly a problem of collecting the DTMF digits to dial a number. Nothing SIP related is taking place yet. The TA5k does not send the INVITE until the dialing-plan in the config says it collected enough digits or it times out.



Alarm panels are essentially a form of modem. You might turn on modem passthrough and ensure that your codecs are forced to G.711. Other codecs don't play well with modem-like applications.

--- TA5k is G711 only but per the above collecting DTMF on it happens before the first INVITE. GR303 is no SIP at all to the metaswitch yet same symptoms.

If the DTMF digits used to set up the call are failing, then there's likely something out of spec with the DTMF encoders in the alarm panels, frequency or twist. Or something different in the call setup like a leading 9 for a PBX that no longer exists. What does the sending Adtran show for the dialed digits on the call?


--- A leading 9 is not the issue but the other things you mentioned seem relevant. I just cannot figure out why the DMS 100 is able to gather the digits so reliably over GR303 yet the Metaswitch is struggling. Let alone the TA5k situation. This gear is pretty industry standard now days. 

--- On the TA5k we tried changing the impedance. The rx/tx-gain. There is truly not much to adjust on the TA5k because these are RPOTS cards. We also had ADTRAN review our config which according to them is quite fine and vanilla. 

--- It really does seem like the fire alarm panel sends a DTMF 95 ms duration digit and it just never gets "detected" by the TA5k or Metaswitch over GR303.


Got a Sage 930A gathering dust on a shelf?

--- Sadly no. 

Using VoIP or anything that requires local power for fire alarms in general is another topic.

--- The TA5k is only a SIP backhaul. Normal pots to the customers. No local power. As for the TA750 example that has battery backup but yea... another topic.


--
Jay Hennigan - jay at west.net
Network Engineering - CCIE #7880
503 897-8550 - WB6RDV

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