Message ID

6

Identifier for Message 6; always 6

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

Sequence number

2

0-3; see § 5.3.1, Annex 2

Destination ID

30

MMSI number of destination station

Retransmit flag

1

Retransmit flag should be set upon retransmission: 0 = no retransmission = default; 1 = retransmitted

Spare

1

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

6-906

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 6 the maximum is 906.

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

112-1 008

For Message 6 the maximum is 920.