Douglas Krantz - Technical Writer - Describing How It Works

How do I Fix the Failure to Communicate Faults?

By Douglas Krantz | Maintenance

How do I Fix the Failure to Communicate Faults?

How do I Fix the Failure to Communicate Faults?

Greetings Douglas,

I'm curious to know if you have a blog, or know of a blog, or technical bulletin regarding the use of fire alarm control panels and both traditional, and modern phone systems.

I am trying to find a logical reasoning of why fire alarm control panels (FACPs) don't always work as well as we may like with modern phone systems. I know the use of the word "Modern" is ambiguous, but there are lots of different methods out there in use.

I know that these FACPs were designed with analog communicators, and didn't work well with Voice over Internet Protocol (VoIP) or Data Subscriber Line (DSL - usually on telephone lines) due to packaging and compression of the analog signal coming from the panel. Then the data package would have to be sent out via digital to a central station receiver, and then uncompressed back to an understandable analog signal. This all had to happen in a time frame that the Digital Alarm Control Transmitter (DACT) would like in order to get a proper kiss-off and avoid a failure to communicate.

Right now, we have a campus that has 6 FACPs. One particular system sends in test timers, and gets failure to communicate simultaneously all day. My understanding is that everything hits digital at some point, if not various points, in the entire transmission line.

The central station mentions that they have other panels that don't have this problem and that it must be a fire alarm panel problem. I argue that the fire alarm panel is just doing exactly what it was designed to do. It's dialing out. and it is getting in touch with the receiver. It seems to be sending the message accurately.

Yes, we want to put them on a Cell communicator, but for some reason decision makers at the campus refuse.

Do you have any easy-to-understand explanation for this phenomenon?

I appreciate any help.

Thank You, TR

The words may be different in each location, but there are two different sites that "Failure to Communicate" fault signals can occur. One is on-site, from the fire alarm communicator (inside the fire alarm control panel, or in a separate communicator). The other is at the off-site central station inside their communication equipment.

The on-site "Failure to Communicate" fault signals indicate the fire alarm communicator has not received a confirmation. This confirmation is the expected "Kiss-Off" from the central station showing that the alarm, supervisory, trouble, or test signal, sent from the on-site communicator.

The On-Site "Failure to Communicate" Message means that the on-site communicator, often located inside the fire alarm control panel, is not receiving the "Kiss-Off" signal back from the off-site monitoring receiver.

The Off-Site "Failure to Communicate" Message means that the off-site receiver at the central station has not received the expected test signal from the on-site communicator.

Class C Pathway

Fire alarm people are very concerned that fire alarm signals get through and do what the signals are supposed to do. Pathways are classified in order to clarify how to expect a signal pathway performs, what happens when a pathway fails, and who gets notified when the pathway isn't working.

For more on the basic pathway classifications, see:

The basic rules to be classified as a Class C pathway are:
  • The pathway uses a handshake signal to supervise the signal path (a Kiss-Off signal is a handshake signal)

  • The pathway can use more than one path (two telephone lines, or a telephone line and a Cell communicator, for instance)

  • The panel shows a trouble signal (like a "Failure to Communicate" signal)


The Kiss-Off signal is actually a supervision signal generated by the off-site communication receiver. The Kiss-Off signal is a supervision signal. It basically says "I have received the entire message and fully understand it".

Whether the originating signal is the newer Contact ID, 4+2, SIAx, etc., the KissOff signal is part of the off-site receiver generated signal.

POTS - Plain-Old-Telephone-System

The old-style communication system built into many fire alarm control panels use a dialup, copper wire, built-in POTS system of communicator. Outside of Radio Frequency (RF) systems or else Direct-Coupled DC copper wire phone line systems, at one time, this was the preferred system of communications.

Nowadays, newer Cell Communicators, VoIP, and/or Web Internet Protocol (IP which includes DSL) gets in-between the POTS output of the communicator and the central station.

Cell Communication

While the Cell Communication system looks on the outside as an equivalent version of the fire alarm's communication POTS signal, the Cell Communication system is vastly shortened. The Cell system just converts each Touch Tone to the number it represents.

Example: On your desk telephone, you press the button marked "6". This produces the two tones mixed together that you hear. Rather than creating a complete digital rendition of the audio, the Cell Communication transmitter converts this two-tone signal to a digital number "6".

In essence, instead of sending a long digital string representing an audio two-tone signal, the Cell transmitter just sends a shortened digital number "6".

With a Cell Communication transmitter, you have to take great care that there at least three different cell phone towers within range of the Cell transmitter. This is because, depending on the user load on each tower, the cell phone company changes towers.

Warning: Before deciding on the exact location of the Cell transmitter's antenna, make sure the antenna has a good RF (Radio Frequency Signal) connection. Perform an RF site survey. Weak RF connections will produce regular "Failure to Communicate" faults, and may prevent an alarm being sent to the central station.

Data String, Packet, and Asynchronous Data

The web uses packets of information.

All digital signals sent from the on-site communicator to the off-site receiver are sent one bit at a time. That's a serial data string. This serial data string is sometimes known as a "Packet".

Because these "packets" of information can be received at any time, the receiver synchronizes itself to the incoming data string. In other words, if the signal transmitter and the signal receiver are designed to work with each other, there isn't a timing problem.

Please note the inclusion of the phrase "designed to work with each other". A cable modem on-site and an internet modem at the central station might not work together.

Warning: Just like regular copper phone lines, the web is prone to damage from backhoes.

Warning: The web signal, originating at the fire alarm system, is dependent on computer servers in other buildings, and sometimes even in other states, in order to always in the "In-Use" mode. If any of these servers is off line for maintenance, both the on-site communication transmitter and the off-site communication receiver at the central station show a trouble signal.

Warning: The in-house web signals often go through patch panels. Make sure a patch cord that carries the alarm signals isn't unplugged. If it's unplugged, plug it back in and somehow prevent it from being unplugged again.

Test Signal

When using the POTS system for communication, the on-site communicator sends a daily "Test" signal. The test is sent out on one dialup phone line per day: the primary phone line one day and the alternate phone line the next.

When the POTS communication system is exclusively used between the fire alarm control panel and the central station, and the phone lines aren't working so the once every 24-hour Kiss-Off signal isn't received, the on-site communicator will show a "Failure to Communicate" error. When the off-site central station doesn't receive the test signal at the expected 24-hour interval, it will also show a "Test Fail" signal.

For supervision purposes, VoIP, DSL, and Cell communication can be considered to be the same as a phone line. It will have the same "Failure to Communicate" and the same "Test Fail" signals. These signals may be once a day, or possibly once every few minutes.

On-site IP (Internet Protocol) communicators often send test signals every few minutes. If the off-site web receiver doesn't receive the test signal, the off-site receiver generates a "Test Fail" every few minutes. If the on-site communicator doesn't receiver the handshake signal, the on-site communicator goes into trouble at that time.

Central Station

When talking to the central station technical support about the signal failures that are happening, keep in mind that they really have no idea of what you have at your end of the pathway. They don't even have a good idea about the path that the alarm signals go through.

Remember that they are assuming that the system worked at one time; now it's not.

The best they can do is to tell you that their end is working because many, many, many other fire alarm systems use the same equipment there, and everybody else's system is working. They can only take guesses as to what might be wrong with the modem or pathway. The modem is a common problem, but sometimes the problem is somewhere between the on-site communication transmitter and the central station.

Example: In a hotel, every first Friday and Saturday of the month, for about two hours from 3:00 AM to 5:00 AM, the fire alarm panel showed "Failure to Communicate" as a trouble.

The hotel was part of a nation-wide franchise system, and their telephones went through the web server at the franchise headquarters on the east coast.

It turned out that the communication path for the on-site fire alarm system went partway across the U S to the franchise server on the east coast, and then to the west coast where the off-site central station was located.

When the server on the east coast was shut down for regular maintenance every month, the fire alarm pathway was blocked. That was the "Failure to Communicate".

Failure to Communicate?

  • Where are the "Failure to Communicate" signals showing up? That can be a clue.

  • How often do the "Failure to Communicate" signals show up? That can be a clue as to what is failing.

  • Are all six fire alarm control panels using the same communicator?

  • Do all six go through the same pathway?

  • Is there a common point, like a local computer server, that all six systems go through?

If you can isolate the problem, the problem becomes easier to fix.

Douglas Krantz
Life Safety
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