How To Solve Common Problems with VOIP and Fire Alarm Systems Dialing Out – Part 1
In this series I will cover common problems with VOIP and fire alarm panels that are connected to an Adtran ATA or Analog Telephone Adapters. Specifically panels that need to dial outbound, inbound requirements and adjustments are somewhat different.
First let me state that nothing replaces a POTS or Plain Old Telephone System line when it comes to life safety devices. So although you may save a ton of money on VOIP the life you save might be your own, if there is a fire or life safety event. You are responsible for keeping the equipment up and running for at least 4 hours in the case of a power outage.
Cheap POTS Lines
That being said it will work, but you will have problems along the way. One alternative is to purchase a low usage POTS line. These are landlines you can purchase from the phone company of your choice that are low usage lines. Low usage lines are used for the explicit purpose of emergency usage like elevators, fire alarm systems, emergency call boxes and burglar alarms. When ordering such a line explain to the sales representative what it will be used for. However VOIP is cheaper and if you are still stuck on converting them then you need to learn how they work and their requirements.
Line Voltage
Since most alarm panels are legacy devices, they could require a higher voltage than what the ATA supplies. The symptoms of low voltage are usually the panel not recognizing the phone line is there and causing a trouble code or false alarm. The simple precaution is to measure the voltage of the normal working panel before you disconnect it. On hook phone line voltage from the phone company is usually between 35 to 48 volts DC. A simple multimeter across the ring and tip can get you this reading, while the phone is on hook.
Since the 1990s most phones are digital and no longer require a battery voltage of 48 volts. So VOIP Analog Telephone Adapters usually only supply 24 to 33 volts of power, this includes PBX equipment with analog cards. If you have an Adtran device with AOS, you can step the voltage up by configuring the command below:
Adtran#conf t Adtran (config)#interface fxs 0/22 Adtran (config-fxs 0/22)#battery-mode high
VOIP Quality Settings
VOIP stand for Voice Over IP which means that you are sending voice over the Internet. When the RTP or Real Time Protocol packets travel over the Internet three problems get injected. The first being latency; every hop creates latency which is the time it takes to route the packet. Other factor to latency could be caused by congestion of the lines or transmission media like cable vs. fiber. The mechanisms that help voice quality, but work against us with modem and faxing is the jitter buffer. The jitter buffer stores UDP datagrams and puts them back in order, it also introduces latency.
The second is echo cancellation, another mechanism that works against us with data on phone lines. Echo cancellation queues the RTP conversation up or down by up to 100ms if an echo is detected. When modems send data it sometimes triggers this and throws the conversation off between transmitter and receiver.
The third is codec related, which applies to compression and decompression of the voice. If you use g729 it will compress audio using a compression algorithm that tends to lose quality of the audio channel, but use less bandwidth. So g711 ulaw should be used for modem lines. You can shut these three mechanisms off automatically by using the command bellow:
Adtran#conf t Adtran (config)# voice user 4125551212 Adtran (config)# modem-passthrough
Once configured, if the DSP or Digital Sound Processor hears a modem signal it will: set the jitter buffer to a fixed value of 50ms, it will turn off echo cancellation and most importantly it will force g711 ulaw (which takes more bandwidth, but does not loose quality of the voice channel).
So if your alarm panel dials up with a modem protocol, then this could be your problem. My recommendation is to listen with a phone or lineman’s butt set while it’s dialing out. If you hear the tell tale modem mating call, these adjustments could solve your problem.
As always if this article helped you please donate or visit some of my sponsors.
For part two follow this link http://www.bohack.com/2012/04/how-to-solve-common-problems-with-voip-and-fire-alarm-systems-dialing-out-part-2/