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

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Presentation on theme: "Transmitting Fire Alarms Reliably After the Sunset of the PSTN Gregory Lapin, PhD, PE King-Fisher Company, inc Lowell, MA."— Presentation transcript:

1 Transmitting Fire Alarms Reliably After the Sunset of the PSTN Gregory Lapin, PhD, PE King-Fisher Company, inc Lowell, MA

2 Topics What is the PSTN? Digital Dialers What is happening to the PSTN? NFPA Requirements How will fire alarms cope? 2November 8, 2011King-Fisher Company, inc

3 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. 3November 8, 2011King-Fisher Company, inc

4 Features of the PSTN Highly reliable (Four 9s = 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. 4November 8, 2011King-Fisher Company, inc

5 Backup Power in the Central Office 5November 8, 2011King-Fisher Company, inc

6 PSTN Quality Voice bandwidth consistent. – 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). 6November 8, 2011King-Fisher Company, inc

7 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 November 8, 2011King-Fisher Company, inc7

8 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. November 8, 2011King-Fisher Company, inc8

9 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. 9November 8, 2011King-Fisher Company, inc

10 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. 10November 8, 2011King-Fisher Company, inc

11 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. 11November 8, 2011King-Fisher Company, inc

12 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. 12November 8, 2011King-Fisher Company, inc

13 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. 13November 8, 2011King-Fisher Company, inc

14 Cord cutting, especially younger segments 14 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 and age groups lived in a mobile-only household. November 8, 2011King-Fisher Company, inc

15 VOIP subscribers will surpass PSTN in PSTN is expected to decline at 9 % annually while VoIP grows at 27% Source: In-Sat and Accenture Estimate US PSTN vs. VoIP Subscribers (M)VoIP Subscribers (%) November 8, 2011King-Fisher Company, inc

16 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. November 8, 2011King-Fisher Company, inc16

17 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). 17November 8, 2011King-Fisher Company, inc

18 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. November 8, 2011King-Fisher Company, inc18

19 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. 19November 8, 2011King-Fisher Company, inc

20 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. November 8, 2011King-Fisher Company, inc20

21 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. November 8, 2011King-Fisher Company, inc21

22 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. November 8, 2011King-Fisher Company, inc22

23 NFPA Regulations NFPA Part 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 November 8, 2011King-Fisher Company, inc

24 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. November 8, 2011King-Fisher Company, inc24

25 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 November 8, 2011King-Fisher Company, inc25

26 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. November 8, 2011King-Fisher Company, inc26

27 Reliability November 8, 2011King-Fisher Company, inc27

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