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CONTENTS

Annex 1 General purpose equipment characteristics
1 General
2 Technical format of a call sequence
3 Dot pattern and phasing
3.4.1 200 bits
3.4.2 20 bits
4 Format specifier
5 Address
6 Category
7 Self-identification
8 Messages
8.5 Test calls
9 End of sequence
10 Error-check character
11 Distress alert attempt
12 Shipborne human machine interface (HMI)
12.1 Shipborne aural alarm
12.2 Inactivity timer
12.3 Display
12.4 MMSI
12.5 Disabling of DSC automatic channel switching function on VHF
12.6 Data interface
12.7 Position updating
12.8 Geographic area entry
12.9 Medical transport and neutral ships and aircraft
Annex 2 Equipment classes
1 Equipment classes only apply to shipborne equipment
2 Class requirements for B, D and E are given in ? 3, 4 and 5 (See Tables 4.1 to 4.10.2 for technical requirements)
3 Class B (MF and/or VHF only)
3.1 Transmit capabilities
3.1.5 Messages
3.2 Receive capabilities
4 Class D (VHF only)
4.1 T r ansmit capabilities
4.1.5 Messages
4.2 Receive capabilities
5 Class E (MF and/or HF only)
5.1 Transmit capabilities
5.1.5 Messages
5.2 Receive capabilities

Recommendation 541-8

(1974,1978,1982-1986-1990-1992,1994-1995-1997)

DIGITAL SELECTIVE CALLING SYSTEM FOR USE IN THE MARITIME MOBILE SERVICE

(Question ITU-R 9/8)

Summary
This Recommendation contains, in Annex 1, the technical characteristics of digital selective calling (DSC) equipment which is used in the maritime-mobile service for calling ships and coast stations including calling for distress and safety purposes. Annex 2 contains the description of various classes of DSC equipment and the more limited technical characteristics of some of those classes.
Associated operational procedures are given in Recommendation ITU-R M.541.

ANNEX 1
General purpose equipment characteristics

1 General
1.1 The system is a synchronous system using characters composed from at ten-bit error-detecting code as listed in Table 1.
1.1.1 The first seven bits of the ten-bit code of Table 1 are information bits. Bits 8, 9 and 10 indicate, in the form of a binary number, the number of B elements that occur in the seven information bits, a Y element being a binary number 1 and a B element a binary number 0. For example, a BYY sequence for bits 8, 9 and 10 indicates 3 (0x4 + 1x2 + 1x1) B elements in the associated seven information bit sequence; and a YYB sequence indicates 6 (1x4 + 1x2 + 0x1) B elements in the associated seven information bit sequence. The order of transmission for the information bits is least significant bit first but for the check bits it is most significant bit first.
1.2 Time diversity is provided in the call sequence as follows:
1.2.1 Apart from the phasing characters, each character is transmitted twice in a time-spread mode; the first transmission (DX) of a specific character is followed by the transmission of four other characters before the re-transmission (RX) of that specific character takes place, allowing for a time-diversity reception interval of:
1.2.1.1 400 ms for HF and MF channels, and
1.2.1.2 33_1/3 ms for VHF radio-telephone channels,
1.3 The classes of emission, frequency shifts and modulation rates are as follows:
1.3.1 F1B or J2B 170 Hz and 100 Bd for use on HF and MF channels. When frequency-shift keying is effected by applying audio signals to the input of single-sideband transmitters (J2B), the centre of the audio-frequency spectrum offered to the transmitter is 1700 Hz.
1.3.2 Frequency modulation with a pr-emphasis of 6 dB/octave (phase modulation) with frequency-shift of the modulating sub-carrier for use on VHF channels:
- frequency-shift between 1300 and 2100 Hz; the sub-carrier being at 1700 Hz;
- the frequency tolerance of the 1300 and 2100Hz tones is ±10 Hz; - the modulation rate is 1200 Bd;
- the index of modulation is 2.0±10%.
1.3.3 The radio-frequency tolerances of new designs of both transmitters and receivers in the MF and HF bands should be:
- coast station: ±10 Hz,
- ship station: ±10 Hz,
- receiver bandwidth: should not exceed 300 Hz.
1.4 The higher frequency corresponds to the B-state and the lower frequency corresponds to the Y-state of the signal elements.
1.5 The information in the call is presented as a sequence of seven-bit combinations constituting a primary code.
1.5.1 The seven information bits of the primary code express a symbol number from 00 to 127, and where:
1.5.1.1 the symbols from 00 to 99 are used to code two decimal figures according to Table 2;
1.5.1.2 the symbols from 100 to 127 are used to code service commands.
1.6 The receiver decoder should provide maximum utilization of the received signal, including use of the error-check character.
1.7 Where the distress call repetitions described in § 11 apply, the following conditions are considered necessary:
1.7.1 the transmitter encoder must provide repetitive transmission of the call sequence in accordance with §11; and
1.7.2 the receiver decoder should provide maximum utilization of the received signal, including use of the error-check character and by using an iterative decoding process with adequate memory provision.
1.8 When the transmission of a DSC distress call is automatically repeated, ships' DSC equipments must be capable of automatically receiving a subsequent distress acknowledgement (see Recommendation ITU-R M.541, Annex 1, § 3.1.3.1, 3.1.3.2 and 3.3.5).
2 Technical format of a call sequence
2.1 The technical format of the call sequence is:
2.2 Examples of typical call sequences and the construction of the transmission format are given in Tables 4 to 7, and in Figs. 1 to 4. 2.3 The flow charts illustrating the operation of the DSC system are shown in Figs. 5a and 5b.
3 Dot pattern and phasing
3.1 The phasing sequence provides information to the receiver to permit correct bit phasing and unambiguous determination of the positions of the characters within a call sequence (see Note 1).
NOTE 1 - Acquisition or character synchronization should be achieved by means of character recognition rather than, for example, by recognizing a change in the dot pattern, in order to reduce false synchronization caused by a bit error in the dot pattern.
3.2 The phasing sequence consists of specific characters in the DX and RX positions transmitted alternatively. Six DX characters are transmitted.
3.2.1 The phasing character in the DX position is symbol No.125 of Table 1.
3.2.2 The phasing characters in the RX position specify the start of the information sequence (i.e. the format specifier) and consist of the symbol Nos. 111, 110, 109, 108, 107, 106, 105 and 104 of Table 1, consecutively.
3.3 Phasing is considered to be achieved when two DXs and one RX, or two RXs and one DX, or three RXs in the appropriate DX or RX positions, respectively, are successfully received. These three phasing characters may be detected in either consecutive or non-consecutive positions but in both cases all bits of the phasing sequence should be examined for a correct 3-character pattern. A call should be rejected only if a correct pattern is not found anywhere within the phasing sequence.
3.4 To provide appropriate conditions for earlier bit synchronization and to allow for scanning methods to monitor several HF and MF frequencies by ship stations. the phasing sequence should be preceded by a dot pattern (i.e. alternating B-Y or Y-B sequence bit synchronization signals) with duration of:
3.4.1 200 bits At HF and MF, for "distress", "distress acknowledgement", "distress relay" and "distress relay acknowledgement" calls and for all calling sequences to ship stations,
3.4.2 20 bits At HF and MF, for all acknowledgement sequences (except distress acknowledgements and distress relay acknowledgements - see § 3.4.1 and Note 1) and for all calling sequences to coast stations (except distress relay calls - see § 3.4,1). At VHF for all calls.
NOTE 1 - In exceptional circumstances and only on national working frequencies the 200 bit dot pattern could also be included in acknowledgement sequences to ship stations.
4 Format specifier
4.1 The format specifier characters which are transmitted twice in both the DX and RX positions (see Fig. 1) are:
4.1.1 symbol No.112 for a "distress" call (RR No.3086 (Appendix S13, Part A3, §1)); or
4.1.2 symbol No.116 for an "all ships" call; or
4.1.3 symbol No.114 for a selective call to a group of ships having a common interest (e.g. belonging to one particular country, or to a single shipowner, etc.); or
4.1.4 symbol No.120 for a selective call to a particular individual station; or
4.1.5 symbol No.102 for a selective call to a group of ships in a particular geographic area; or
4.1.6 symbol No.123 for a selective call to a particular individual station using the semi-automatic/automatic service.
4.2 It is considered that receiver decoders must detect the format specifier character twice for "distress" calls and "all ships" calls to effectively eliminate false alerting. For other calls, the address characters provide additional protection against false alerting and, therefore, single detection of the format specifier character is considered satisfactory (see Table 8).
5 Address
5.1 "Distress" calls and "all ships" calls do not have addresses since these calls are implicitly addressed to all stations (ship stations and coast stations).
5.2 For a selective call directed to an individual ship, to a coast station or to a group of stations having a common interest, the address consists of the characters corresponding to the station's maritime mobile service identity, the sequence consisting of characters coded in accordance with Table 2 (see Note 1).
NOTE 1 - According to RR ex Appendix 43 (Article S19), maritime mobile service identities are formed of a series of nine digits, consisting of three digits of the Maritime Identification Digits (MID) and six more digits.
These identities are included in the address and self-identification parts of the call sequence and are transmitted as five characters C5C4C3C2C1, comprising the ten digits of:

(X₁,X₂) (X₃,X₄) (X₅,X₆) (X₇,X₈) and (X₉,X₁₀)

respectively. whereas digit X₁₀ is always the figure 0 unless the equipment is also designed in accordance with Recommendation ITU-R M.1080.
Example:

MID X₄ X₅ X₆ X₇ X₈ X₉ being the ship station identity is transmitted by the DSC equipment as:

(M,I) (D,X₄) (X₅,X₆) (X₇,X₈) (X₉,0)

5.3 For a selective call directed to a group of ships in a particular geographic area a numerical geographic coordinates address consisting of ten digits (i.e. 5 characters), is constructed as follows (see Fig. 6 and Note 1):
NOTE 1 - In order to comply with commonly accepted practice, the order of entry and read-out should be: first latitude and then longitude.
5.3.1 the designated geographic area will be a rectangle in Mercator projection;
5.3.2 the upper left-hand (i.e. North-West) comer of the rectangle is the reference point for the area;
5.3.3 the first digit indicates the azimuth sector in which the reference point is located, as follows:
5.3.3.1 quadrant NE is indicated by the digit "0",
5.3.3.2 quadrant NW is indicated by the digit "1",
5.3.3.3 quadrant SE is indicated by the digit "2",
5.3.3.4 quadrant SW is indicated by the digit "3":
5.3.4 the second and third digits indicate the latitude of the reference point in tens and units of degrees;
5.3.5 the fourth, fifth and sixth digits indicate the longitude of the reference point in hundreds, tans and units of degrees:
5.3.6 the seventh and eighth digits indicate the vertical (i.e. North-to-South) side of the rectangle, L, in tens and units of degrees;
5.3.7 the ninth and tenth digits indicate the horizontal (i.e. West-to-East) side of the rectangle, L, in tens and units of degrees.
6 Category
6.1 The "category" information is coded as shown in Table 9 and defines the degree of priority of the call sequence.
6.2 For a "distress" call the priority is defined by the format specifier and no category information is included in the call sequence.
6.3 For safety related calls, the "tcategory" information specifies:
6.3.1 distress (RR No. N3143/S32.40); or
6.3.2 urgency; or
6.3.3 safety.
6.4 For other calls, the "category" information specifies:
6.4.1 ship's business; to cater for shore-to-ship communications having priority category 6 as defined in RR No. 4441/S53.1. Some coast stations do not use the ship's business priority category;
6.4.2 routine.
7 Self-Identification
7.1 The maritime mobile service identity (MMSI) assigned to the calling station, coded as indicated in §5.2 and its Note 1, is used for self-identification. The MMSI should be stored in the DSC unit and it should not be possible for the user to easily change it.
8 Messages
The messages that are included in a call sequence contain the following message elements, which are listed in the order in which they would appear in each message:
8.1 For a "distress" call (see Table 4 and Fig.4a)) the distress information is contained in four, messages in the following order:
8.1.1 Message 1 is the "nature of distress" message, coded as shown in Table 10, i.e.:
8.1.1.1 fire, explosion;
8.1.1.2 flooding;
8.1.1.3 collision;
8.1.1.4 grounding;
8.1.1.5 listing, in danger of capsizing;
8.1.1.6 sinking;
8.1.1.7 disabled and adrift;
8.1.1.8 undesignated distress;
8.1.1.9 abandoning ship;
8.1.1.10 piracy/armed robbery attack;
8.1.1.11 man overboard;
8.1.1.12 emergency position-indicating radiobeacon (EPIRB) emission.
8.1.2 Message 2 is the "distress coordinates" message, consisting of ten digits indicating the location of the vessel in distress, coded on the principles described in Table 2, in pairs starting from the first and second digits (see Note 1 to §5.3):
8.1.2.1 The first digit Indicates the quadrant in which the incident has occurred. as follows:
8.1.2.1.1 quadrant NE is indicated by the digit "0",
8.1.2.1.2 quadrant NW is indicated by the digit "1",
8.1.2.1.3 quadrant SE is indicated by the digit "2",
8.1.2.1.4 quadrant SW is indicated by the digit "3".
8.1.2.2 The next four figures indicate the latitude in degrees and minutes.
8.1.2.3 The next five figures indicate the longitude in degrees and minutes.
8.1.2.4 If "distress coordinates" cannot be included, or if the position information has not been updated for 23_1/2 hours, the 10 digits following the "nature of distress" should be automatically transmitted as the digit 9 repeated 10 times.
8.1.2.5 DSC equipment should be provided with facilities for automatic position updating in accordance with NMEA-0183 (or IEC-1162) for input of data from a navigation equipment.
8.1.3 Message 3 is the time indication (UTC) when the coordinates were valid consisting of four digits coded on the principles described in Table 2, in pairs starting from the first and second digits.
8.1.3.1 The first two digits indicate the time in hours.
8.1.3.2 The third and fourth digits indicate the part of the hours in minutes.
8.1.3.3 If the time cannot be included the four time indicating digits should be transmitted automatically as "8 8 8 8".'
8.1.4 Message 4 is a single character to indicate the type of communication (telephone or teleprinter) which is preferred by the station in distress for subsequent exchange of distress traffic (RR No.N3143/S32.40). This character is coded as shown in Table 11.
8.2 For other types of calls (see Table 5 and Figs.2 and 3) except "distress relay", "distress relay acknowledgement" and "distress acknowledgement" calls (see § 8.3), two messages are included in the following order:
8.2.1 Message 1 is the "telecommand" information and consists of 2 characters (first and second telecommand) coded as shown in Tables 11 and 12:
8.2.1.1 if no information additional to that conveyed by the first telecommand character is required, then the second telecommand signal should be symbol No.126 (no information) - see Table 12;
8.2.1.2 if no telecommand information is used, symbol No.126 is transmitted twice.
8.2.2 Message 2 may contain two "channel or frequency message" elements, each of which always consists of three characters, "character 1", "character 2" and "character 3", indicating the proposed working frequency (in the F1B/J2B mode the assigned frequency should be used) in multiples of 100 Hz or the channel number (coded in accordance with Table 13) or the ship's position. The first frequency element (the RX field) in the call indicates the called station receive frequency and the second frequency element (the TX field) indicates the called station transmit frequency. In acknowledgements the RX and TX fields indicate the receive and transmit frequency of the acknowledging station respectively (see also Fig. 2 and Note 1).
NOTE 1 - If only one channel or frequency message element is used, this indicates the called station receive channel or frequency or a two-frequency (paired) channel. A second channel or frequency message element may be used to designate the called station transmit channel or frequency. If the calling station indicates only the called station receive frequency (for broadcast mode transmissions) then the symbol No. 126 repeated three times should be transmitted instead or the called station transmit channel or frequency message element. If no "channel or frequency message" elements are used, the symbol No.126 is transmitted six times. For calls using the semi-automatic/automatic VHF service (see Table 7) then only one "channel or frequency message" element is transmitted which indicates the paired channel number. In the absence of this element the symbol No.126 should be transmitted three times.
8.2.2.1 Frequency information
The frequency (in the F1B/J2B mode the assigned frequency should be used) in multiples of 100 Hz may only be indicated as such when the frequency is below 30 MHz. The three characters provide for the required six decimal digits. Character 1 represents the units (U) and tens (T) of 100 Hz, character 2 the hundreds (H) and thousands (M) and character 3 the tens of thousands (TM) and hundreds of thousands (HM) of 100 Hz.
8.2.22 Channel information
8.2.2.2.1 HF and MF channels If the HM digit is 3, this indicates that the number represented by the digits TM, M, H, T and U is the HF/MF working channel number (either single frequency or two frequency channels).
8.2.2.2.2 VHF channels If the HM digit is 9, this indicates that the number represented by the values of the digits M, H, T and U is the VHF working channel number. If the M digit is 1, this Indicates that the ship stations transmitting frequency is being used as a simplex channel frequency for both ship and coast stations. If the M digit Is 2, this indicates that the coast stations transmitting frequency is being used as a simplex channel frequency for both ship and coast stations.
8.2.2.3 Ship's position information
8.2.2.3.1 Message 2 may contain the ship's position, consisting of the digit 5 repeated two times and ten digits (five characters) indicating this position, coded in accordance with §8.1.2 to §8.1.2.3 (see Table 14).
8.2.2.3.2 If a reply to a calling sequence requesting ship's position is required (see Fig. 3d) then message 2 consists of twelve digits (six symbols), the first of which should be coded in accordance with §8.1.2 to §8.1.2.3 followed by one symbol No.126.
8.2.2.3.3 Message 3 follows message 2 in this case and contains the time (UTC) when the coordinates were valid, coded as indicated in §8.1.3 to §8.1.3.3.
8.2.3 Message 3 follows message 2 when using the DSC system for calls initiated by ship stations requiring a semi-automatic or automatic connection (see Table 7) and contains the public switched network number (e.g. telephone number). In this case the format specifier used is symbol No.123.
8.2.3.1 This number is coded by up to nine symbols in a manner similar to that shown in Table 2, except that the first character transmitted should be either symbol No.105 or No.106 to indicate whether the network number contains an odd or even number of significant digits. As an example, the number 0012345 would be coded as symbol numbers 105 00 0l 23 45 whereas the number 00123456 should be coded as symbol numbers 106 00 12 34 56.
8.3 For "distress relay" including shore-to-ship alerts, "distress relay acknowledgement" and "distress acknowledgement" calls, the message formats are indicated in Figs. 4b) and 4c) respectively.
8.3.1 For a distress relay where the identity of the station in distress is unknown, the "identification of the station in distress" should be automatically transmitted as the symbol No.126 five times.
8.3.2 Distress call cancellation To cancel an inadvertent transmitted "distress" call, a "distress cancellation" call in the format indicated in Fig. 4c) may be transmitted with the ship's own MMSI inserted as identification of ship in distress. This cancellation should be followed immediately by a voice cancellation procedure, as described in Recommendation ITU-R M.541.
8.4 For test calls on the exclusive distress and safety calling frequencies on MF and HF, the call sequence is given in Table 6 (see also Recommendation ITU-R M.541, Annex 1). Technical means should be included to prevent the transmission of this sequence on VHF. Furthermore, the first telecommand symbol No.118 (see Table 3) should only be capable of being inserted into the sequence given in Table 6.
9 End of sequence
The "end of sequence" (EOS) character is transmitted three times in the DX position and once in the RX position (see Fig. lb). It is one of the three unique characters corresponding to symbol Nos. 117, 122 and 127 as follows:
9.1 symbol No.117 if the call requires acknowledgement (Acknowledge RQ);
9.2 symbol No.122 if the sequence is an answer to a call that requires acknowledgement (Acknowledge BQ):
9.3 symbol No.127 for all other calls.
10 Error-check character
10.1 The error-check character (ECC) is the final character transmitted and it serves to check the entire sequence for the presence of errors which are undetected by the ten-unit error-detecting code and the time diversity employed.
10.2 The seven information bits of the ECC shall be equal to the least significant bit of the modulo-2 sums or the corresponding bits of all information characters (i.e. even vertical parity). The format specifier and the EOS characters are considered to be information characters. The phasing characters and the retransmission (RX) characters shall not be considered to be information characters. Only one format specifier character and one EOS character should be used in constructing the ECC. The ECC shall also be sent in the DX and RX positions.
10.3 Automatic acknowledgement transmission should not start unless the ECC is received and decoded correctly. A received ECC which does not match that calculated from the received information characters may be ignored if this was due to an error detected in the ten-unit error-detecting code or the information characters which was correctable by use of the time diversity code.
11 Distress call attempt
11.1 Distress calls may be transmitted as a single frequency or a multi-frequency call attempt preceded by a dot pattern. Where a distress call attempt contains more than one consecutive distress call on the same frequency (see Recommendation ITU-R M.541, Annex 1, §3.1.3), these consecutive calls may be transmitted with no gap between the end of one call and the start of the dot pattern of the following call to enable bit synchronization to be maintained (see Fig. 1c)).
11.2 A distress call should be activated only by means of a dedicated distress button which should be clearly identified and be protected against inadvertent operation. The initiation of a distress call should at least require two independent actions.
11.3 Calls with format specifier "distress" or category "distress", "urgency" and "safety" should be initiated manually only. This applies also for ships equipped for automatic DSC operation. For automatic repetition of distress calls see Recommendation ITU-R M.541, Annex 1, §§3.1.3 and 3.3.5.
12 Audible alarm
An audible alarm and visual indicator should he provided upon reception of a distress call or a call with category distress(see Recommendation ITU-R M.541, § 3).

ANNEX 2
Equipment classes

1
Class A equipment. which includes all the facilities defined in Annex 1, will comply with the IMO GMDSS carriage requirements for MF/HF installations.
Class B equipment providing minimum facilities for equipment on ships not required to use Class A equipment and complying with the minimum IMO GMDSS carriage requirements for MF and/or VHF installations.
Class D equipment is intended to provide minimum facilities for VHF DSC distress, urgency and safety as well as routing calling and reception, not necessarily in toll accordance with IMO GMDSS carriage requirements for VHF installations.
Class E equipment is intended to provide minimum facilities for MF and/or HF DSC distress, urgency and safety, as well as routine calling and reception, not necessarily in till accordance with IMO GMDSS carriage requirements for MF/HF installations.
Class F equipment is intended to provide for VHF DSC distress, urgency and safety calling and also for reception of acknowledgements to its own distress calls (in order to terminate the transmission) (see Note 1).
Class G equipment is intended to provide for MF DSC distress, urgency and safety calling and also for reception of acknowledgements to its own distress calls (in order to terminate the transmission).
NOTE 1 - Class C equipment as defined in earlier versions of this Recommendation (e.g., Recommendation ITU-R M.493-5 (Geneva. 1992)) has been replaced by Class F equipment.

2 The technical requirements for Class B, D, E, F and G are given in §3,4,5,6 and 7 below.
3 Class B (MF and/or VHF only)
3.1 Transmit capabilities

3.1.2 The numerical identification of the called station (address).

3.1.4 Self-Identification (automatically inserted).

3.1.5 Messages
3.1.5.1 For distress calls:
Message 1: Nature of distress, defaulting to undesignated distress
Message 2: Distress coordinates
Message 3: Time for last position update
Message 4: Type of subsequent communication: MF: H3E or J3E; VHF: F3E/G3E simplex
3.1.5.2 For distress relay calls:

3.1.5.3 For distress acknowledgement calls:

3.1.5.4 For all other calls:

3.1.6 End of sequence character: as defined in Annex 1.

3.2 Receive capabilities
3.2.1 Receive and be capable of displaying all the information in calls listed in § 3.1 plus all distress relay calls having the format specifier "geographical area calls", all distress acknowledgement calls and all "unable to comply" calls.
3.2.2 Audible alarm upon reception of any DSC call.
4 Class D (VHF only)
4.1 Transmit capabilities

4.1.2 The numerical Identification of the called station (address).

4.1.4 Self-identification (automatically inserted).
4.1.5 Messages
4.1.5.1 For distress calls:
Message 1 Nature of distress, defaulting to undesignated distress
Message 2: Distress coordinates
Message 3: Time for last position update
Message 4: Type of subsequent communication: F3E/G3E simplex.
4.1.5.2 For all other calls:

4.1.6 End of sequence character: as defined in Annex 1.
4.2 Receive capabilities
Receive and be capable of displaying all the information in calls listed in § 4.1 plus all distress relay calls except those having the format specifier "geographical area calls", all distress acknowledgement calls and all "unable to comply" calls.
5 Class E (MF and/or HF only)
5.1 Transmit capabilities

5.1.2 The numerical identification of the Called station (address).

5.1.4 Self-identification (automatically inserted).
5.1.5 Messages
5.1.5.1 For distress calls:
Message 1: Nature of distress, defaulting to undesignated distress
Message 2: Distress coordinates
Message 3: Time for last position update
Message 4: Type of subsequent communication: H3E or J3E
5.1.5.2 For all other calls:

5.1.6 End of sequence character: as defined in Annex 1.
5.2 Receive capabilities Receive and be capable of displaying all the information in calls listed in § 5.1 plus all distress relay calls having the format specifier "geographical area calls", all distress acknowledgement calls and all "unable to comply" calls.
6 Class F (VHF only)
6.1 Transmit capabilities

6.1.3 Self-identification (automatically Inserted).
6.1.4 Messages
6.1.4.1 For distress calls:
Message 1: Undesignated distress
Message 2: Distress coordinates (see Note 1)
Message 3: Time for last position update (see Note 1)
Message 4: F3E/G3E simplex.
NOTE 1 - The distress coordinates and time information may be provided solely by means of the interface specified in Annex 1, § 8.1.2.5. In the absence of this information, Annex 1, § 8.1.2.4 and 8.1.3.3 apply.
6.1.4.2 For all other calls:

6.2 Receive capabilities
The equipment should be able to receive acknowledgements to its own distress calls.
7 Class G (MF only)
7.1 Transmit capabilities:

7.1.3 Self-Identification (automatically inserted).
7.1.4 Messages
7.1.4.1 For distress calls:
Message 1: Undesignated distress
Message 2: Distress coordinates (see Note 1 of § 6.1.4.1)
Message 3: Time for last position update (see Note 1 of §6.1.4.1)
Message 4: J3E telephony.
7.1.4.2 For other calls:

7.2 Receive capabilities
The equipment should be able to receive acknowledgements to its own distress calls.