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:

  1. 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
  2. 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
  3. Event type (see below)
  4. Areas affected (up to 32), designated by FIPS state code and indicating the county (parish in Louisiana, borough or census area in Alaska), but which may be designated for the whole state by using county number 000.
  5. Duration of alert, normally in increments of 15 minutes from time of issue
  6. Exact time of issue, in UTC, without time zone adjustments
  7. Eight-character station callsign identification, with / used instead of - .

Contents

[edit] Full Message Breakdown

An EAS message contains these elements, in this transmitted sequence:

  1. Header: (Preamble) ZCZC-org-eee-pssccc-pssccc+tttt-jjjhhmm-llllllll
  2. Attention signal (1050 Hz audio tone for Weatheradio, combined 853 and 960 Hz tones for commercial radio/TV)
  3. Message - audio, video image or video text
  4. 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

  1. EAN: Emergency action notification
  2. EAT: Emergency action termination
  3. RMT: Required monthly test
  4. RWT: Required weekly test

[edit] Optional

  1. ADR: Administrative message
  2. AVA: Avalanche watch
  3. AVW: Avalanche warning
  4. BHW: Biological hazard warning
  5. BWW: Boil water warning
  6. BZW: Blizzard warning
  7. CAE: Child abduction emergency*
  8. CDW: Civil danger warning
  9. CEM: Civil emergency message
  10. CFA: Coastal flood watch
  11. CFW: Coastal flood warning
  12. CHW: Chemical hazard warning
  13. CWW: Contaminated water warning
  14. DBA: Dam watch
  15. DBW: Dam break warning
  16. DEW: Contagious disease warning
  17. DMO: Demonstration message
  18. DSW: Dust storm warning*
  19. EQW: Earthquake warning*
  20. EVA: Evacuation watch
  21. EVI: Evacuation immediate
  22. FCW: Food contamination warning
  23. FFA: Flash flood watch
  24. FFS: Flash flood statement
  25. FFW: Flash flood warning
  26. FLA: Flood watch
  27. FLS: Flood statement
  28. FLW: Flood warning
  29. FRW: Fire warning*
  30. FSW: Flash freeze warning
  31. FZW: Freeze warning
  32. HLS: Hurricane statement
  33. HMW: Hazardous materials warning*
  34. HUA: Hurricane watch
  35. HUW: Hurricane warning
  36. HWA: High wind watch
  37. HWW: High wind warning
  38. IBW: Iceberg warning
  39. IFW: Industrial fire warning
  40. LAE: Local area emergency*
  41. LEW: Law enforcement warning*
  42. LSW: Land slide warning
  43. NAT: National audible test
  44. NIC: National Information Center
  45. NMN: Network message motif*
  46. NPT: National periodic test
  47. NST: National silent test
  48. NUW: Nuclear plant warning*
  49. POS: Power outage statement
  50. RHW: Radiological hazard warning*
  51. SMW: Special marine warning*
  52. SPS: Special weather statement
  53. SPW: Shelter in place warning*
  54. SVA: Severe thunderstorm watch
  55. SVR: Severe thunderstorm warning
  56. SVS: Severe weather statement
  57. TOA: Tornado watch
  58. TOE: 911 telephone outage emergency*
  59. TOR: Tornado warning
  60. TRA: Tropical storm watch
  61. TRW: Tropical storm warning
  62. TSA: Tsunami watch
  63. TSW: Tsunami warning
  64. TXB: Transmitter backup on
  65. TXF: Transmitter carrier off
  66. TXO: Transmitter carrier on
  67. TXP: Transmitter primary on
  68. VOW: Volcano warning*
  69. WFA: Wild fire watch
  70. WFW: Wild fire warning
  71. WSA: Winter storm watch
  72. WSW: Winter storm warning
  73. ??A: Unrecognized watch
  74. ??E: Unrecognized emergency
  75. ??S: Unrecognized statement
  76. ??W: Unrecognized warning

(*new codes added in 2002)

Aural example of SAME transmission

[edit] See also

[edit] External links