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, 8, 25 or 26. The acknowledge required flag should not be set when using the broadcast message 8.

Permitted as from:

01/02/2014

Registrant:

ITU-R.M.1371-5

Physical link:

AIS

Message number (0=VDES-VDE):

DAC or VPFI:

FI / Message ID:

State:

in force

Number of slots (max):

Last modified:

29/01/2021 - 23:19

Details:

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 Message 6	Broadcast binary Message 8	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.