Technical concept Emergency Alert System

1 technical concept

1.1 primary entry point (pep) stations
1.2 communication links

1.2.1 limitations


1.3 eas header

technical concept

messages in eas composed of 4 parts: digitally encoded same header, attention signal, audio announcement, , digitally encoded end-of-message marker.

a sage eas endec unit.

the  same header (help·info) critical part of eas design. contains information originated alert (the president, state or local authorities, national weather service (noaa/nws), or broadcaster), short, general description of event (tornado, flood, severe thunderstorm), areas affected (up 32 counties or states), expected duration of event (in minutes), date , time issued (in utc), , identification of originating station (see same complete breakdown of header).

77 radio stations designated national primary stations in primary entry point (pep) system distribute presidential messages other broadcast stations , cable systems. emergency action notification notice broadcasters president of united states or his/her designee deliver message on eas via pep system.

primary entry point (pep) stations

pep stations private or commercial radio broadcast stations cooperatively participate fema provide emergency alert , warning information public before, during, , after incidents , disasters. fema pep stations serve primary source of initial broadcast presidential emergency action notification (ean). pep stations equipped additional , backup communications equipment , power generators designed enable them continue broadcasting information public during , after event. integrated public alert , warning system (ipaws) program management office (pmo) expanding number of participating broadcast stations across nation directly cover on 90 percent of u.s. population. pep station expansion ensure under conditions president of united states can alert , warn public.

in september 2009, fema contracted u.s. army corps of engineers (usace) equip selected radio stations become fema primary entry point (pep) stations. project usace actively bringing new stations fema pep program. high level tasks activating new pep station include: initial site assessments, environmental assessments, design specifications, construction of special facilities, , coordinating memorandums of agreement stations , activity coordination state, territorial, tribal, , local jurisdictions , fema regional offices.

pep stations provide resilience alerts , warnings public. ipaws program management office (pmo) modernizing existing pep stations next generation alert , warning equipment include common alert protocol (cap) compliance equipment, , internet protocol enabled equipment.

satellite communications infrastructure can integrated legacy emergency alert system (eas) , provides reliable, redundant commercial system utilizing multiple uplinks , satellites national level eas distribution. ipaws pmo continues complete integration of satellite data transmission paths diverse path eas message delivery fema pep stations. xm radio transmission path completed in first quarter of 2010, , direct satellite connectivity became available national pep stations in third quarter of 2010.

the ipaws eas modernization , pep expansion project includes , maintains 77 operational pep stations throughout united states , territories. direct coverage of nation s population expand approximately 67 percent in 2009 on 90 percent when 77 pep stations become operational in 2015.

communication links

the fema national radio system (fnars) provides primary entry point service emergency alert system , , acts emergency presidential link eas. fnars net control station located @ mount weather emergency operations center.

once ean received eas participant pep station (or other participant) message daisy chains through network of participants. daisy chains form when 1 station receives message multiple other stations , station forwards message multiple other stations. process creates many redundant paths through message may flow increasing likelihood message received participants , adding survivability of system.

each eas participant required monitor @ least 2 other participants.

limitations

in new york times article (correction printed january 3, 2002)

no president has ever used current [eas] system or technical predecessors in last 50 years, despite soviet missile crisis, presidential assassination, oklahoma city bombing, major earthquakes , 3 recent high-alert terrorist warnings...michael k. powell, chairman of federal communications commission, oversees emergency alert system, pointed ubiquitous media environment, arguing system was, in effect, scooped cnn, msnbc, fox news channel , other channels... [fema] activates alert system nationally @ behest of white house on 34 50,000-watt stations reach 98 percent of americans... beyond that, current eas signal audio message – pre-empts programming – viewers watching color images of world trade center on september 11 have been able see screen generic text message along presidential voice-over, if emergency message had been activated.

eas header

because header lacks error detection codes, repeated 3 times redundancy. however, repetition of data can considered error detection , correction code – error detection or correction code, adds redundant information signal in order make errors identifiable. eas decoders compare received headers against 1 another, looking exact match between two, eliminating errors can cause activation fail. decoder decides whether ignore message or relay on air if message applies local area served station (following parameters set broadcaster).

the same header bursts followed  attention signal (help·info) lasts between 8 , 25 seconds, depending on originating station. tone  1050 hz (help·info) on noaa weather radio (noaa/nws) station, while on commercial broadcast stations, consists of 2 tone combination of 853 hz , 960 hz sine waves, same 1 used older emergency broadcast system. these tones have become infamous, considered both frightening , annoying many viewers; indeed, 2 tones chosen because form interval suited getting audience s attention due unpleasantness on human ear. same header equally known shrillness, many have found startling. 2 tone system no longer required of 1998, , used audio alerts before eas messages. ebs, attention signal followed voice message describing details of alert.

a gorman-redlich rack mounted cap-to-eas converter translates cap formatted alerts eas headers.

the message ends 3 bursts of afsk eom , or end of message, text nnnn, preceded each time binary 10101011 calibration.

the white house endorsed integration of common alerting protocol (cap) in presidential initiative, , fema in process of testing implementation.