Transmitting Fire Alarms Reliably After the Sunset of the PSTN Gregory Lapin, PhD, PE King-Fisher...

Transmitting Fire Alarms Reliably After the

Sunset of the PSTN

Gregory Lapin, PhD, PE

King-Fisher Company, inc

Lowell, MA

Topics

• What is the PSTN?• Digital Dialers• What is happening to the PSTN?• NFPA Requirements• How will fire alarms cope?

2November 8, 2011 King-Fisher Company, inc

What is the PSTN?

• Public Switched Telephone Network

– A regulated monopoly.– Governed by FCC and state regulations.– 100-years old.– Almost all forms of telephone communication

rely on the PSTN to some extent.– Available anywhere in the USA at a

reasonable price.


Features of the PSTN• Highly reliable (Four 9’s = 99.99% availability)

– How many times have you lost power at home but your old landline telephone still worked?

• Dedicated hardware– Every telephone line has its own pair of wires connecting

you to the Central Office.– When calls are combined in “trunks” your call has time

slots reserved for your voice only.

• Line powered– Backup power available for at least 24 hours.– Often good for a week or more.– Power is delivered directly to the end-of-line devices.


Backup Power in the Central Office


PSTN Quality

• Voice bandwidth consistent.– 300-3400 Hz ; not Hi-Fi but understandable.

• Low Latency– Less than 100 msec, usually < 40 msec.

• No voice drop outs.• Standard CODECs (A-Law and μ-Law).• Time to Dial Tone (< 0.5 sec).• Time to Disconnect (< 2 sec).


Regulated Monopoly

• The PSTN has been the telephone system in the US for 100 years.

• Prices are fixed by the state commerce commissions.

• PSTN is available anywhere in the USA.– Subsidized by USF for rural and low income

• Independent competition to the PSTN was first allowed in 1984.

November 8, 2011 King-Fisher Company, inc 7

Regulated Monopoly

• PSTN must meet operating standards specified in FCC rules.

• PSTN is used/required for use in many parts of the overall communications landscape:– PSAPs (911) only connected via PSTN.– PSTN provides the link between many

different telecommunications vendors.


Digital Dialers

• The most common method of reporting fire alarms to the emergency dispatch.– There are about 40 million digital dialers in

use in the United States; many are used to report fire alarms.

• Also known as DACTs.


Digital Dialers

• Modem devices that send alarms by telephone.

• Designed around the characteristics of the PSTN.

• Convert digital data to tones.• Depend on precise timing of signals.• Depend on continuity of communications.


Digital Dialers

• Digital dialers fail when:– There is insufficient voice bandwidth.– There are dropouts in the audio transmission.– There are excessive delays in transmission.– CODEC does not match standards.– There is too much voice compression.


Digital Dialers

• Do not work well over cellular networks.• Can be unreliable on VOIP networks.

– Central Station Alarm Association warns against VOIP connections.

• Must be used on networks with at least 24 hours of backup power.


What is Replacing PSTN?

• Cellular Telephones.• Voice Over IP (VOIP).

– Skype.– MagicJack.– Cable TV Telephone Service.

• e.g. Comcast Xfinity, Cox.

– Fiber Optic Telecommunications Service.• e.g. Verizon FIOS, ATT Uverse.


14

Cord cutting, especially younger segments

Source: National Center for Health Statistics

• As of May 2010, 23% of respondents in a study lived in a mobile-only household.• The same study also found that 37% of adults in the 18-24 and 30-34 age groups lived in a

mobile-only household.

November 8, 2011 King-Fisher Company, inc

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VOIP subscribers will surpass PSTN in 2013

2007 2008 2009 2010 2011 2012 2013 2014 2015 20160

20

40

60

80

100

120

140

160

180

PSTN VOIP

PSTN is expected to decline at 9 % annually while VoIP grows at 27%Source: In-Sat and Accenture Estimate

54%

46%

Residential Business

US PSTN vs. VoIP Subscribers (M) VoIP Subscribers (%)

November 8, 2011 King-Fisher Company, inc

Sunset of the PSTN

• PSTN is already more expensive to maintain than competing services.

• As the number of PSTN subscribers continues to decrease the cost of maintaining service increases.

• Current trends indicate that by 2018 the PSTN will no longer be viable and will be abandoned as a regulated monopoly.


Characteristics of VOIP

• Audio is digitized, packetized and included with other data on the IP link.– This can include digital television signals and Internet

data.

• Audio Bandwidth usually not a problem.• Multiple connections share single physical path.

– Statistical Multiplexing combines the calls.– Dropouts are poorly controlled.– Latency is poorly controlled.– Timing is uneven (jitter).


Control of VOIP• VOIP over public Internet does not permit control

of many parameters.• VOIP over private networks (Cable TV, Fiber

Optics) allows parameters to be customized to work with DACTs, but:– Providers attempt to maximize throughput and can

decrease performance on the fly.– The only indication that a connection no longer

supports DACT is if the daily test fails.– Often the incompatibility is intermittent and may pass

the daily test but not work all the time.


Other VOIP Concerns

• For most VOIP installations the connection depends on the following items at your location:– Computer.– Router.– Data Modem.

• Backup Power for these items include UPS and vendor-supplied backup battery.

• Total backup time is usually a few hours.


What About Cellular Technology?

• Current DACTs work poorly over Cellular Telephones.– Special modems have been developed that work well

on Cellular Networks.

• Cellular networks are likely to be overloaded during even a commonplace disaster.

• Many Cellular towers have a maximum of 8 hours of backup power; some have much less.


SMS (or “Text Messaging”)

• Text messaging would seem to be a natural mode for transmitting alarms.

• Cellular carriers do not recommend its use for emergency communications because:– All text messages share the same frequency

channel.– Cellular networks do not guarantee timely

delivery of text messages.


NFPA Regulations

• For alarm communications, NFPA regulations strive to meet 3 basic principles:– Alarm delivery must occur within a specified

time (End-to-End duration < 90 seconds).– Alarm communications must have at least 2

independent redundant paths available.– Alarms must be detected and delivered up to

24 hours following loss of primary power.


NFPA RegulationsNFPA Part 72-2010

26.6.3.2.1.4 Transmission Channels.

(A) A system employing a DACT shall employ one telephone

line (number). In addition, one of the following transmission

means shall be employed:

(1) A second telephone line (number)

(2) A cellular telephone connection

(3) A one-way radio system

(4) A one-way private radio alarm system

(5) A private microwave radio system

(6) A two-way RF multiplex system

(7) A transmission means complying with 26.6.3.1


NFPA Regulations

• Multiple telephone “lines” over a VOIP connection are really different data packets on the same wire.

• All data handled by the same electronics.• This does not meet the intent of

independent redundant signal paths as put forth by NFPA.


Digital Dialers Make No Sense for the Future

• A digital dialer is designed for an analog communications system:– It converts digital messages to analog tones.– If analog tones are transmitted over a digital

communications system (VOIP or Cell Phone):• Analog tones are converted to digital bits.• At the other end, digital bits are converted to analog tones.• The digital dialer receiver converts the analog tones to the

digital message.

• Digital - Analog - Digital - Analog - Digital


What Can We Do?• Start replacing Digital Dialers now!

– Over the next 6 years, 40 million of these devices must be changed to other technologies.

• Replace the redundant telephone line with a different modality, such as radio, for true redundancy.

• Look forward to a time when new technology will provide direct digital access to the IP.– Make sure all future IP connections have sufficient

backup power to meet NFPA standards.


Reliability


Transmitting Fire Alarms Reliably After the Sunset of the PSTN Gregory Lapin, PhD, PE King-Fisher...

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