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Y1-03-0222 Rev. C
6. Regional Assignment Channel Assignment Message (NMEA 0183 ACA)
A Nauticast™-B unit can receive regional channel management information in two ways: ITU-R M.1371
message 22 or a DSC telecommand received on channel 70. Channel management information is applied
based upon the actual location of the AIS device. An AIS unit is “using” channel management information when
the information is being used to manage the operation of the VHF receiver and/or transmitter inside the AIS unit.
This sentence is used both to enter and obtain channel management information. When sent to an AIS unit, the
ACA sentence provides regional information that the unit stores and uses to manage the internal VHF radio.
When sent from an AIS unit, the ACA sentence provides the current channel management information retained
by the AIS unit. The information contained in this sentence is similar to the information contained in an ITU-R
M.1371-1 message 22. The information contained in this sentence directly relates to the Initialization Phase and
Dual Channel Operation and Channel Management functions of the AIS unit as described in ITU-R M. 1371.
ACA message format
$--ACA,x,llll.ll,a,yyyyy.yy,a,llll.ll,a,yyyyy.yy,a,x,xxxx,x,xxxx,x,x,x,a,x,hhmmss.ss
field 1 2 3 4 5 6 7 8 91011121314 15
Field
Format
Description
1
x
Sequence Number , 0 to 9
2
IIII, II, a
Region Northeast corner latitude – N/S
3
yyyyy.yy,a
Region Northeast corner longitude – E/W
4
IIII, II, a
Region Southwest corner latitude – N/S
5
yyyyy.yy,a
Region Southwest corner longitude – E/W
6
x
Transition Zone Size
7
xxxx
Channel A
8
x
Channel A bandwidth
9
xxxx
Channel B
10
x
Channel B bandwidth
11
x
Tx/Rx mode contro
12
x
Power level control
13
a
Information source
14
x
In-Use Flag
15
hhmmss.ss
Time of "in-use" change
7. Channel management information source messages (NMEA 0183 ACS)
This sentence is used in conjunction with the ACA sentence. This sentence identifies the originator of the
information contained in the ACA sentence and the date and time the AIS unit received that information.
ACS message format
!-- ACS,x,xxxxxxxxx, hhmmss.ss,xx,xx,xxxx*hh<CR><LF>
field 1 2 3 4 5 6
Field
Format
Description
1
x
Sequence Number , 0 to 9
2
xxxxxxxxx
MMSI of originator
3
hhmmss.ss
UTC of receipt of channel management information
4
xx
UTC Day, 01 -31
5
xx
UTC Month, 01 -12
6
xxxx
UTC Year