DTMF timing issue with alarm panel communications 3

[kelrodjr]

Let me start off by saying that I am a fire alarm technician by trade. I don't know much about phone systems.

I service a campus-like site with many small buildings. There are 40+ fire alarm panels at this site which all communicate with an alarm receiver via analog copper phone lines through a Meridian PBX. Recently we have been replacing some of the older fire alarm systems with newer panels. The newer panels utilize Ademco Contact ID as the preferred reporting protocol. For those not familiar with Contact ID, a brief overview can be found here: [URL unfurl="true"]http://li0r.wordpress.com/contact-id-protocol/[/url]

Contact ID signals are transmitted in groups of 16 DTMF digits; each digit has a duration of 50 ms followed by 50 ms of silence. The standard relies on specific timing of the digit and receiver acknowledgement tones.

What is happening on this site is that the PBX seems to be "slowing down" the DTMF tones to the alarm receiver. The signals sound okay with proper 50 ms timing from the fire alarm panels inbound to the PBX; however outbound from the PBX to the receiver the DTMF tones are being lengthened to about 200 ms. The receiver never gets a chance to acknowledge the signals before the fire alarm panel tries to resend them. Unfortunately the people who manage the PBX have no clue how to fix this, so here I am. I would appreciate any help!

 

[Funk49]

I'll let the the more experienced techs weigh in as I'm still learning this system but a quick search in the manual showed a setting in LD 17 under "DTRB" (DigiTone BuRst) time in ms.
Choices are 50ms, 60ms, 70ms and the default 100ms

I'm a little curious about this as well. We have emergency phone boards (Janus?) installed in our elevators and the disconnect DTMF codes work intermittently. I am suspecting a DTMF duration as well.

 

[kstaff22]

I had an issue similar to this a couple years ago---the equiptment was Digital Communication Standard -
Ademco ® Contact ID Protocol -
for Alarm System
Communications
SIA DC-05-1999.09

If this PBX is a 1000E (it has media gateways and uses DSP's to send traffic between them --also does ip to tdm conv.
In-band DTMF tones that originate from an analog set or incoming trunk are filtered out of the media stream by the dsp of the Voice Gateway media card.

Cause of the problem appeared to be that DTMF tones from the dialer were being created at much faster rate than they were delivered. Originating dialer was finished sending and waiting for ACK and retransmitting even before the destination could finish receiving the first batch of tones.

This was eventually corrected by disabling "DTMF Tone Detection" for the media gateway in Element Manager.



 
 


 

[KCFLHRC]

I had a very similar issue also. I moved an analog card into the same media gateway as my local PRI and solved the issue. That way no VGW channel is involved.