IALA

Text using 6-bit ASCII

TABLE 27
International function message 0 using Message 25, broadcast or addressed binary message
Parameter Number of bits Description
Message ID 6 Identifier for Message 25; always 25
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
Destination indicator 1 0 = Broadcast (no Destination ID field used)
1 = Addressed (Destination ID uses 30 data bits for MMSI)
Binary data flag 1 Always 0
Destination ID 0/30 Destination ID if used. If Destination indicator = 0 (Broadcast), no data bits are needed for Destination ID.
If Destination indicator = 1, 30 bits are used for Destination ID and spare bits for byte alignment.
Spare 0/2 Spare (if Destination ID used)
DAC 10 International DAC = 110 = 00000000012
FI 6 Function identifier = 010 = 0000002
Text sequence number 11 Sequence number to be incremented by the application.
All zeros indicates that sequence numbers are not being used.
Text string 6-66/6-96 6-bit ASCII as defined in Table 47, Annex 8. When using this IFM, the number of slots used for transmission should be 1 taking into account Table 29.
For Message 25 the maximum is 66 for Addressed or 96 for Broadcast.
Spare bits Max 7 Not used for data and should be set to zero. The number of bits should be either 1, 3, 5 or 7 to maintain byte boundaries.
NOTE 1 – When a 7-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 and 13.
Total number of application data bits 112-168/
80-168
112-168 bits for Addressed, or 80-168 bits for Broadcast.

 

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.