Specific Area Message Encoding
From Wikipedia, the free encyclopedia
Specific Area Message Encoding or SAME is the protocol used to encode the Emergency Alert System in the U.S. for broadcast stations. It was originally created for NOAA Weather Radio by the National Weather Service, and was later adopted by the FCC for regular broadcasters on radio, television, and cable, as well as by Environment Canada for its weather radio service.
The system transmits digital tones over normal audio using AFSK, with a 2083.3 Hz mark tone and 1562.5 Hz space tone, lasting 1920 μs (1.92 ms) each. The data is encoded in 7-bit ASCII but uses all 8 bits, with no parity bit and no stop bit ("8-N-0"), at a bitrate of 520.83 bits per second. The least significant bit of each byte is transmitted first.
In the SAME system, messages are constructed in four parts, the first and last of which are digital. The first part is the AFSK-encoded header message in 7-bit ASCII text. It is repeated three times, so that decoders can pick "best two out of three" for each byte, thereby eliminating most errors which can cause an activation to fail. The text of the header code contains:
- A preamble of binary 10101011 (0xAB in hex) repeated sixteen times, used for "receiver calibration", then the letters ZCZC as an attention to the decoder
- Information about the originator of the alert:
- EAN - national authorities, including the President
- CIV - civil authorities, such as president, governor or local city/county emergency management agency
- WXR - National Weather Service weatheradio
- EAS - broadcasters, such as radio & TV stations, or cable TV companies
- Event type (see below)
- Areas affected (up to 32), usually designated by county (or parish in Louisiana, or borough in Alaska), but which may be designated for the whole state by using county number 000.
- Duration of alert, normally in increments of 15 minutes from time of issue
- Exact time of issue, in UTC, without time zone adjustments
- Eight-character station callsign identification, with / used instead of - .
Contents |
[edit] Full Message Breakdown
An EAS message contains these elements, in this transmitted sequence:
- Header: (Preamble) ZCZC-org-eee-pssccc-pssccc+tttt-jjjhhmm-llllllll
- Attention signal (1050 Hz audio tone for Weatheradio, combined 853 and 960 Hz tones for commercial radio/TV)
- Message - audio, video image or video text
- Tail: (Preamble) NNNN (EOM)
There is one second of blank audio between each section, and before and after each message.
- (Preamble): Signal that clears and resets the receiving system; factory-programmed
- ZCZC: Start of ASCII code; factory-programmed
- org: Originator code; programmed per unit when put into operation
- eee: Event code; programmed at time of event
- pssccc: County-location codes (up to 32 locations); programmed at time of event
- ss is the state or equivalent water area code
- ccc is the county/borough/parish, independent city, or equivalent (000 for entire state)
- p is the part of the county, or 0 for the entire county
- tttt: Duration the alert is valid (hhmm format); programmed at time of event
- jjjhhmm: Date and Time-of-Day; encoded automatically, based on settings
- jjj is the Julian date day of the year, in UTC, with leading zeros
- hhmm is 24-hour hours and minutes, in UTC, with leading zeros
- llllllll: Eight-Character ID; programmed per unit when put into operation
- broadcast station callsign, such as WXXX/FM
- NWS location, such as KDEN/NWS for Denver, Colorado
- Attention signal: Sent if any message is included (normally sent with all messages except RWT); must be at least eight seconds long
- NNNN: End-of-message code (EOM)
[edit] Event codes
There are two types of event codes, four that are required to be encoded in every unit used, and other optional headers that users may program
[edit] Required
- EAN: Emergency action notification
- EAT: Emergency action termination
- RMT: Required monthly test
- RWT: Required weekly test
[edit] Optional
- ADR: Administrative message
- AVA: Avalanche watch
- AVW: Avalanche warning
- BHW: Biological hazard warning
- BWW: Boil water warning
- BZW: Blizzard warning
- CAE: Child abduction emergency*
- CDW: Civil danger warning
- CEM: Civil emergency message
- CFA: Coastal flood watch
- CFW: Coastal flood warning
- CHW: Chemical hazard warning
- CWW: Contaminated water warning
- DBA: Dam watch
- DBW: Dam break warning
- DEW: Contagious disease warning
- DMO: Demonstration message
- DSW: Dust storm warning*
- EQW: Earthquake warning*
- EVA: Evacuation watch
- EVI: Evacuation immediate
- FCW: Food contamination warning
- FFA: Flash flood watch
- FFS: Flash flood statement
- FFW: Flash flood warning
- FLA: Flood watch
- FLS: Flood statement
- FLW: Flood warning
- FRW: Fire warning*
- FSW: Flash freeze warning
- FZW: Freeze warning
- HLS: Hurricane statement
- HMW: Hazardous materials warning*
- HUA: Hurricane watch
- HUW: Hurricane warning
- HWA: High wind watch
- HWW: High wind warning
- IBW: Iceberg warning
- IFW: Industrial fire warning
- LAE: Local area emergency*
- LEW: Law enforcement warning*
- LSW: Land slide warning
- NAT: National audible test
- NIC: National Information Center
- NMN: Network message motif*
- NPT: National periodic test
- NST: National silent test
- NUW: Nuclear plant warning*
- POS: Power outage statement
- RHW: Radiological hazard warning*
- SMW: Special marine warning*
- SPS: Special weather statement
- SPW: Shelter in place warning*
- SVA: Severe thunderstorm watch
- SVR: Severe thunderstorm warning
- SVS: Severe weather statement
- TOA: Tornado watch
- TOE: 911 telephone outage emergency*
- TOR: Tornado warning
- TRA: Tropical storm watch
- TRW: Tropical storm warning
- TSA: Tsunami watch
- TSW: Tsunami warning
- TXB: Transmitter backup on
- TXF: Transmitter carrier off
- TXO: Transmitter carrier on
- TXP: Transmitter primary on
- VOW: Volcano warning*
- WFA: Wild fire watch
- WFW: Wild fire warning
- WSA: Winter storm watch
- WSW: Winter storm warning
- ??A: Unrecognized watch
- ??E: Unrecognized emergency
- ??S: Unrecognized statement
- ??W: Unrecognized warning
(*new codes added in 2002)
Aural example of SAME transmission
[edit] See also
- Common Alerting Protocol (CAP) - A SAME-compatible digital format for multi-system warning coordination.
