Ship  23 knots 2 s Ship  23 knots and changing course 2 s (1) When a mobile station determines that it is the semaphore (see § 3.1.1.4, Annex 2), the reporting interval should decrease to 2 s (see § 3.1.3.3.2, Annex 2). NOTE 1 – These values have been chosen to minimize unnecessary loading of the radio channels while maintaining compliance within the IMO AIS performance standards. NOTE 2 – If the autonomous mode requires a shorter reporting interval than the assigned mode, the Class A shipborne mobile AIS station should use the autonomous mode. TABLE 2 Reporting intervals for equipment other than Class A shipborne mobile equipment Platform’s condition Nominal reporting interval Increased reporting interval Class B “SO” shipborne mobile equipment not moving faster than 2 knots 3 min 3 min Class B “SO” shipborne mobile equipment moving 2−14 knots 30 s 30 s Class B “SO” shipborne mobile equipment moving 14−23 knots 15 s 30 s(3) Class B “SO” shipborne mobile equipment moving >23 knots 5 s 15 s(3) Class B “CS” shipborne mobile equipment not moving faster than 2 knots 3 min – B “CS” shipborne mobile equipment moving faster than 2 knots 30 s – Search and rescue aircraft (airborne mobile equipment) 10 s(2) – Aids to navigation 3 min – AIS base station 10 s(1) – base station’s reporting interval (RI) should decrease to 3 1/3 s after the station detects that one or more stations are synchronizing to the base station (see § 3.1.3.3.1, Annex 2). (2) Shorter RI down to 2 s could be used in the area of search and rescue operations. (3) Class B “SO” AIS shall report at the “Increased reporting interval” only when the last four consecutive frames each have less than 50% Free slots. Class B “SO” AIS shall not return to the “Normal reporting interval” until 65% or more of the slots of each of the last four consecutive frames are free. 5 Frequency band AIS stations should be designed for operation in the VHF maritime mobile band, with 25 kHz bandwidth, in accordance with RR Appendix 18 and Recommendation ITUR M.1084, Annex 4. The minimum requirement for certain of equipment may be a subset of the VHF maritime band.
Spurious emissions –36 dBm 9 kHz ... 1 GHz –30 dBm 1 GHz ... 4 GHz Intermodulation attenuation (base station only) 40 dB 6 Definitions of timing for Figure 2 Reference Bits Time (ms) Definition T0 0 0 Start of transmission slot. Power should NOT exceed –50 dB of Pss before T0 TA 0-6 0-0.625 exceeds –50 dB of Pss TB TB1 6 0.625 Power should be within +1.5 or –3 dB of Pss TB2 8 0.833 Power should be within +1.5 or –1 dB of Pss (start of training sequence) TE (includes 1 stuffing bit) 233 24.271 should remain within +1.5 or –1 dB of Pss during the period TB2 to TE TF (includes 1 stuffing bit) 241 25.104 Power should be –50 dB of Pss and stay below this TG 256 26.667 Start of next transmission time period TABLE 7 Minimum required time division multiple access receiver characteristics(1) Receiver parameters Requirements Sensitivity 20% PER @ –107 dBm Error behaviour at high input levels 1% PER @ –77 dBm 1% PER @ –7 dBm Adjacent channel selectivity 20% PER @ 70 dB Co-channel selectivity 20% PER @ 10 dB Spurious response rejection 20% PER @ 70 dB Intermodulation response rejection 20% PER @ 74 dB Spurious emissions –57 dBm (9 kHz to 1 GHz) –47 dBm (1 GHz to 4 GHz) Blocking 20% PER @ 86 dB (1) For Class B “SO”, Table 36 in Annex 7 applies.
Unused bits in the last byte should be set to zero in order to preserve byte boundary. Generic example for a message table: 17 Parameter Symbol Number of bits Description P1 T 6 Parameter 1 P2 D 1 Parameter 2 P3 I 1 Parameter 3 P4 M 27 Parameter 4 P5 N 2 Parameter 5 Unused 0 3 Unused bits Logical view of data as described in § 3.3.7: Bit order M----L-- M------- -------- -------- --LML000 Symbol TTTTTTDI MMMMMMMM MMMMMMMM MMMMMMMM MMMNN000 Byte order 1 2 3 4 5 Output order to VHF data link (bit-stuffing is disregarded in the example): Bit order --L----M -------M -------- -------- 000LML-- Symbol IDTTTTTT MMMMMMMM MMMMMMMM MMMMMMMM 000NNMMM Byte order 1 2 3 4 5 3.3.7.1 Message identification The message ID should be 6 bits long and should range between 0 and 63. The message ID should identify the message type. 3.3.7.2 Self-organizing time division multiple access message structure The SOTDMA message structure should supply the necessary information in order to operate in accordance with § 3.3.4.4. The message structure is shown in Fig. 17. 17 3.3.7.2.1 User identification The user identification (User ID) should be the MMSI (see § 3, 1). The MMSI is 30 bits long. The first 9 digits (most significant digits) should be used only. 3.3.7.2.2 Self-organizing time division multiple access communication The communication state provides the following functions: – it contains information used by the slot allocation algorithm in the SOTDMA concept;
29 Estimated number of slots Maximum number of 6-bit 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 accounts for the worst case bit stuffing condition. 5.2 International function message 2: Interrogation for a specific functional message IFM 2 should be used by an application to interrogate (using Message 6) another application for the specified functional message. The application responding to this interrogation should use an addressed binary message to reply. TABLE 30 Parameter Number of bits Description 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 1 Not used. Should be zero DAC 10 International DAC = 110 = 00000000012 FI 6 Function identifier = 210 = 0000102 Requested DAC code 10 IAI, RAI or test Requested FI code 6 See appropriate FI reference document(s) Spare bits 64 Not used, should be set to zero, reserved for future use Total number of bits 168 The resulting Message 6 occupies 1 slot.
23 Group assignment command Assignment of a specific report behaviour by competent authority using a Base station to a specific group of mobiles 1 FATDMA, RATDMA N/A B 24 Static data report Additional data assigned to an MMSI Part A: Name Part B: Static Data 4 RATDMA, CSTDMA, FATDMA N/A M/B 25 Single slot binary message Short unscheduled binary data transmission (Broadcast or addressed) 4 RATDMA, ITDMA, CSTDMA, FATDMA N/A M/B 26 Multiple slot binary message with State Scheduled binary data transmission (Broadcast or addressed) 4 SOTDMA, RATDMA, ITDMA FATDMA SOTDMA, ITDMA M/B 27 Position report for applications Class A and Class B “SO” shipborne mobile equipment outside base station coverage 1 MSSA N/A M
Message 13 should be used as an acknowledgement of up to four Message 12 messages received (see § 5.3.1, Annex 2) and should be transmitted on the channel, where the addressed message to be acknowledged was received. These acknowledgements should be applicable only to the VHF data link (see § 5.3.1, Annex 2). Other means must be employed for acknowledging applications. 56 Parameter Number of bits Description Message ID 6 Identifier for Messages 7 or 13 7 = binary acknowledge 13 = safety related acknowledge 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 of this acknowledge (ACK) Spare 2 Not used. Should be set to zero. Reserved for future use Destination ID1 30 MMSI number of first destination of this ACK Sequence number for ID1 2 Sequence number of message to be acknowledged; 0-3 Destination ID2 30 MMSI number of second destination of this ACK; should be omitted if no destination ID2 Sequence number for ID2 2 Sequence number of message to be acknowledged; 0-3; should be omitted if no destination ID2 56 (end) Parameter Number of bits Description Destination ID3 30 MMSI number of destination of this ACK; should be omitted if no destination ID3 Sequence number for ID3 2 Sequence number of message to be acknowledged; 0-3; should be omitted if no destination ID3 Destination ID4 30 MMSI number of fourth destination of this ACK; should be omitted if no destination ID4 Sequence number for ID4 2 Sequence number of message to be acknowledged; 0-3. Should be omitted if there is no destination ID4 Number of bits 72-168 3.6 Message 8: Binary broadcast message This message will be variable in length, based on the amount of binary data. The length should vary between 1 and 5 slots. TABLE 57 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; default = 0; 3 = do not repeat any more Source ID 30 MMSI number of source station