In the realm of fire safety, reliable communication is paramount. Whether it’s a commercial facility, or industrial complex, the ability to swiftly communicate emergencies to the relevant authorities can mean the difference between containment and catastrophe. When considering the communication infrastructure for fire alarm systems, several options have been available in the past, among the most common choices are Voice over Internet Protocol (VoIP), Plain Old Telephone Service (POTS), and Cellular Lines.
A Brief history on Alarm Signal Transmissions
The alarm industry began before the advent of telephones. At the time, the only way to transmit signals from a customer’s premise to a central monitoring station was by telegraph lines. After telephones became the main vehicle for communication, alarm
signals were transmitted via a system of leased lines from the old “phone companies”. Leased lines were not only expensive to use, they were also not the most reliable, especially in inclement weather.
Starting in the 1970s, companies started making alarm panels that transmitted signals over the public switched telephone network (PSTN) using plain old telephone (POTS)lines. POTS lines, which used copper wires, was a reliable technology over which to transmit signals as power for the service was provided by the phone company. In otherwords, if there was a power outage at a building, phone service would not have been
interrupted. A very good feature for sending signals when life and property are involved.
In the 1980’s, the use of POTS lines became approved for transmitting fire alarm signals. To make sure there was some redundancy for the transmission of signals,NFPA 71 (the National Fire Alarm Code Standard that became part of NFPA 72 in 1990) required that two phone lines be used when a commercial fire alarm system was
to transmit signals over POTS lines. Additionally, the alarm panel would send a test signal to the central station to check in once every 24 hours to ensure the panel was“online.” Signals were sent from the customer’s premise to the central station in a
similar way to how one fax machine called another fax machine. The panel at the customer’s premise dialed a receiver line at the central station and would be answered just like a fax machine. Because the end user provided the lines and the technology was more reliable than the older telegraph type lines, the industry shifted to using POTS lines for alarm systems.
POTS lines remained the most common form of alarm signal transmission until the phone companies shifted away from PSTN and started using VoIP (voice over internet protocol), FCC Forbearance Order 19-72A1 requires that all POTS Lines in the U.S. be replaced with an alternative service by August 2, 2022. The order effectively ushers in an end-of-life scenario for traditional analog copper POTS line systems while cellular
radio and the internet became the faster methods of communication. The transition from the use of POTS lines to internet and/or digital cellular took time. For one thing, the Nation’s cellular network was in its infancy and its reliability was a concern. The use of
internet for alarm signal transmission was also new and the performance of the Nation’s internet network under adverse conditions (such as a power outage) was a concern. However, it was clear to the industry and the Standards making bodies that a shift from
the use of POTS lines to newer technologies was inevitable, so the Standards were changed to include the newer technologies and how they were to be used.
The Shift to Modern Signal Transmission
In today’s world, the Internet is used all over, cellular networks are robust and POTS lines have either been phased out or will be gone forever soon. VoIP lines (a phone line number provided by your cable provider) are available but do not have the same type of redundancy as POTS lines did and signals are not transmitted as quickly as when using cell or internet. Additionally, while you may get two phone line numbers with VoIP, they will be delivered over one cable so if that cable is cut, both lines will be lost. The use of Internet and digital cellular provides reliability, speed and redundancy. An alarm system is installed to reduce the risk of loss due to a fire or burglary. Having a signal sent to a central monitoring facility to promptly notify the fire or police will further reduce the risk of loss. Saving 20 seconds in alarm signal transmission time could make
a significant difference. By having two separate communication paths (using either wireless with cell or internet) as well as two separate technologies (internet and digital cellular) a building’s system has built in redundancy to get an alarm signal successfully
transmitted. Additionally, the cost of transmitting a signal using digital and cell is less than what two phone lines cost.
Alarm reporting formats require a handshake and a kiss-off so that the panel knows when to start and stop transmitting, as well as a checksum to ensure that the signal was not corrupted in some way. However, when the signal is digitized and compressed by fiber equipment, the signal may not be transmitted or received reliably. Sometimes the handshake, checksum, or kiss-off is chopped off or compromised causing the panel to report improper information and or redial multiple times. Some alarm panels allow a technician to program a slower reporting transmission speed, which makes the compression have less impact. However, this is unreliable. The precise amount of compression is unpredictable and depends on the exact route the call takes. Therefore, slowing the transmission speed doesn’t always work, or work reliably. In addition, the
slower the transmission speed, the higher the chance that the signal will be interrupted or that the telephone line will be compromised, which is why signals were designed to be sent quickly in the first place.
Worse, security professionals can no longer be sure that their alarm signals will never be digitized on its way to the central station. There is a good likelihood that the signal will pass a fiber node somewhere, even if the premises still has a copper connection. Since codes and technologies are always changing, it’s important to be aware of the changes and ensure your systems utilize the best transmission method(s) available from both a performance and a price perspective. Right now, using internet and digital cellular for a system’s alarm signal transmission methods accomplishes both.
