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

[Matthew Yaklin]

> --- 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.

OK, so the FXS port of the local Adtran device isn't reliably decoding the DTMF from the panel. Could be frequency, level, or twist. See if there are knobs for receive level and/or impedance for the specific line port used by the panel. I'd start with level, bump it up and down 3dB at a time and see if it starts decoding reliably. If possible bracket it to see where it fails again and set it in the middle.

Changing impedance might help if it's twist. Sometimes the options include series capacitance. Likely going to be trial-and-error.

------ That is exactly what we tried. Modifying the settings available in the TA5000. So here is what you have to play with.

PLBGNY01AT0#show running-config interface fxs 1/7/23 verbose
!
interface fxs 1/7/23
  description "default adtran settings shown"
  impedance 900c
  rx-gain -4.0
  tx-gain -4.0
  signaling loop-start
  alarm enable line-showering
  alarm enable trunk-conditioning
  alarm enable over-temperature
  no shutdown

=======================

PLBGNY01AT0(config-fxs 1/7/23)#impedance
600r                        - 600 Ohms
900c                        - 900 + 2.16uF
auto                        - Automatically select the impedance
z1                          - 220 + (820 || 115nF)
z2                          - 270 + (750 || 150nF)
z3                          - 270 + (750 || 150nF), Zin = 600
z4                          - 320 + (1050 || 230nF)
z5                          - 350 + (1000 || 210nF), Zin = 600
z6                          - 370 + (620 || 310nF)
z7                          - 800 || (100 + 50nF), Zin = 900 + 2.16uF
z8                          - 1650 || (100 + 5nF), Zin = 900 + 2.16uF

=============================

PLBGNY01AT0(config-fxs 1/7/23)#tx-gain
<-6.0-9.0>                  - Gain in 0.1dB increments
PLBGNY01AT0(config-fxs 1/7/23)#rx-gain
<-10.0-6.0>                 - Gain in 0.1dB increments

==================

And I hate to say this I brute forced them all pretty much. Tried each impedance. Forced the alarm panel to dial out by disconnecting the battery backup in it. Then adjusted tx and rx gain. For the alarm panel to dial. Etc...

I read docs such at this to improve my understanding and many others: https://www.cisco.com/c/en/us/support/docs/voice/ip-telephony-voice-over-ip-voip/64282-impedance-choice.html

I never had to try this hard to get a normal pots line working to an alarm panel over copper or T1 delivered pots to a channel bank.

Matt




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

_______________________________________________
VoiceOps mailing list
VoiceOps at voiceops.org
https://puck.nether.net/mailman/listinfo/voiceops