Text using 6-bit ASCII

Introduction/Additional information: 

This IFM should be used by a ship or base station to send 6-bit ASCII text telegram to other AIS stations. The text telegram can be sent with either binary message 6 or 8. The acknowledge required flag should not be set when using the broadcast message 8.

Registrant: 
ITU-R.M.1371-3
Message number: 
8
DAC: 
1
FI: 
0
State: 
in force
Number of slots (max): 
5
Permitted as from: 
01/06/2007
Details: 
TABLE 26
International function message 0 using Message 8, broadcast binary message
Parameter Number of bits Description
Message ID 6 Identifier for Message 8; always 8
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
Source ID 30 MMSI number of source station
Spare 2 Not used. Should be zero
DAC 10 International DAC = 110 = 00000000012
FI 6 Function identifier = 010 = 0000002
Acknowledge required flag 1 1 = reply is required, optional for addressed binary messages and not used for binary broadcast messages
0 = reply is not required, optional for an addressed binary message and required for binary broadcast messages
Text sequence number 11 Sequence number to be incremented by the application.
All zeros indicates that sequence numbers are not being used
Text string 6-936 6-bit ASCII as defined in Table 47, Annex 8. When using this IFM, the number of slots used for transmission should be minimized taking into account Table 29.
For Message 8 the maximum is 936.
Spare bits Max 6 Not used for data and should be set to zero. The number of bits should be either 0, 2, 4, or 6 to maintain byte boundaries.
NOTE 1 – When a 6-bit spare is needed to satisfy the 8-bit byte boundary rule, the 6-bit spare will be interpreted as a valid 6-bit character (all zeros is the “@” character). This is the case when the number of characters is: 1, 5, 9, 13,17, 21, 25, etc.
Total number of application data bits 80-1 008  
 
TABLE 29
Estimated number
of slots
Maximum number of 6-bit ASCII characters
based upon typical bit stuffing
Addressed binary
Message 6
Broadcast binary
Message 8
Message 25 Message 26
Addressed
binary
Broadcast
binary
Addressed
binary
Broadcast
binary
1 6 11 6 11 2 7
2 43 48 40 45
3 80 86 77 82
4 118 123 114 120
5 151 156 150 163
NOTE 1 – The 5-slot value accounts for the worst case bit stuffing condition.