Channel management

msg_ID: 
22
Description: 
Management of channels and transceiver modes by a Base Station
Priority: 
1
Access scheme: 
FATDMA
RATDMA
Communication state: 
N/A
Transmitted by: 
Base station

This message should be transmitted by a base station (as a broadcast message) to command the VHF data link parameters for the geographical area designated in this message and should be accompanied by a Message 4 transmission for evaluation of the message within 120 NM. The geographical area designated by this message should be as defined in § 4.1, Annex 2. Alternatively, this message may be used by a base station (as an addressed message) to command individual AIS mobile stations to adopt the specified VHF data link parameters. When interrogated and no channel management performed by the interrogated base station, the not available and/or international default settings should be transmitted (see § 4.1, Annex 2).
TABLE 75

Parameter Number of bits Description
Message ID 6 Identifier for Message 22; always 22
Repeat indicator 2 Used by the repeater to indicate how many times a message has been repeated. See § 4.6.1, Annex 2; 0-3; 0 = default; 3 = do not repeat any more
Station ID 30 MMSI number of Base station
Spare 2 Not used. Should be set to zero. Reserved for future use
Channel A 12 Channel number of 25 kHz simplex or simplex use of 25 kHz duplex in accordance with Recommendation ITU-R M.1084.
Channel B 12 Channel number of 25 kHz simplex or simplex use of 25 kHz duplex in accordance with Recommendation ITU-R M.1084.
Tx/Rx mode 4 0 = Tx A/Tx B, Rx A/Rx B (default)
1 = Tx A, Rx A/Rx B
2 = Tx B, Rx A/Rx B
3-15: not used
When the dual channel transmission is suspended by Tx/Rx mode command 1 or 2, the required reporting interval should be maintained using the remaining transmission channel
Power 1 0 = high (default), 1 = low
Longitude 1,
(or 18 most significant bits (MSBs) of addressed
station ID 1)
18 Longitude of area to which the assignment applies; upper right corner
(North-East); in 1/10 min, or 18 MSBs of addressed station ID 1
(±180°, East = positive, West = negative)
181 = not available
Latitude 1,
(or 12 least significant bits (LSBs) of addressed
station ID 1)
17 Latitude of area to which the assignment applies; upper right corner (North‑East); in 1/10 min, or 12 LSBs of addressed station ID 1, followed by 5 zero bits
(±90°, North = positive, South = negative)
91° = not available
Longitude 2,
(or 18 MSBs of addressed
station ID 2)
18 Longitude of area to which the assignment applies; lower left corner
(South-West); in 1/10 min, or 18 MSBs of addressed station ID 2
(±180°, East = positive, West = negative)
Latitude 2,
(or 12 LSBs of addressed
station ID 2)
17 Latitude of area to which the assignment applies; lower left corner
(South-West); in 1/10 min, or 12 LSBs of addressed station ID 2, followed by 5 zero bits (±90°, North = positive, South = negative)
Addressed or broadcast message indicator 1 0 = broadcast geographical area message = default; 1 = addressed message
(to individual station(s))
Channel A bandwidth 1 0 = default (as specified by channel number);
1 = spare (formerly 12.5 kHz bandwidth in Recommendation
ITU-R M.1371-1 now obsolete)
Channel B bandwidth 1 0 = default (as specified by channel number);
1 = spare (formerly 12.5 kHz bandwidth in Recommendation
ITU-R M.1371-1 now obsolete)
Transitional zone size 3 The transitional zone size in nautical miles should be calculated by adding 1 to this parameter value. The default parameter value should be 4, which translates to 5 nautical miles; see § 4.1.5, Annex 2
Spare 23 Not used. Should be set to zero. Reserved for future use
Number of bits 168  

NOTES:

  • If the precision provided within the Latitude and Longitude field of an IEC 61162 exceeds a resolution of 1/10 min the value should be truncated for Message 22 content.
  • Some Class B “CS” units are only operational on the upper half of the maritime VHF band.
  • Narrow-band channel management operation is no longer supported.