Coding the Maritime User Protocol (General)

The Maritime User Protocol can be used to code either the vessel’s mobile service identity number (MMSI) or its Radio Call Sign (if it has 6 or fewer characters). Confusion between the two options is eliminated because the Radio Call Sign includes letters whereas the MMSI is composed entirely of digits.

Coding the Maritime User Protocol with MMSI

Bits 40 – 75 can be coded to designate the last 6 digits of the 9-digit MMSI using the modified-Baudot code shown in the table below.

Special care must be taken when coding this protocol in situations where the National administration has been allocated more than one country code (bits 27 – 36). When this option is used it is critical that the country code provided in bits 27 – 36 correspond to the first 3 digits of the vessel’s MMSI code.

Coding the Maritime User Protocol with the Radio Call Sign

Radio call signs of up to six characters can be encoded if the call sign complies with the ITU Radio Regulations on the formation of call signs (Article S19 of the Radio Regulations). This regulation requires that if alphabetic characters exist in the call sign, they can only occur in the first 4 characters. Consult the Radio Regulations for the complete requirements for establishing radio call signs.

Up to 6 alphanumeric characters using the modified-Baudot code presented in the table below can be accommodated with this protocol. If the radio call sign has fewer than 6 characters, blank spaces should be encoded to the left of the characters using the modified-Baudot symbol “100100”. If the radio call sign has seven characters it can only be encoded using the Radio Call Sign Protocol.

 

Modified-Baudot Code
Letter	Code	Letter	Code	Figure	Code
A	111000	N	100110	Space	100100
B	110011	O	100011	Hyphen	011000
C	101110	P	101101	/	010111
D	110010	Q	111101	0	001101
E	110000	R	101010	1	011101
F	110110	S	110100	2	011001
G	101011	T	100001	3	010000
H	100101	U	111100	4	001010
I	101100	V	101111	5	000001
J	111010	W	111001	6	010101
K	111110	X	110111	7	011100
L	101001	Y	110101	8	001100
M	100111	Z	110001	9	000011

The coding information to be used for each protocol is further described by clicking on the appropriate section of the table below.

Maritime User Protocol

	Unmodulated Carrier (160ms)
Bit Synch	Bit Synch Pattern	Bits 1 – 15	15 Bits
Frame Synch	Frame Synch Pattern	Bits 16 – 24	9 Bits
First  Protected  Data Field	0	Bit 25	1 Bit
	1	Bit 26	1 Bit
	Country Code	Bits 27 – 36	10 Bits
	Identification	Bits 37 – 85	49 Bits
	0 1 0	Bits 37 – 39	3 Bits
	MMSI or Radio Call Sign	Bits 40 – 75	36 Bits
	Specific Beacon Number	Bits 76 – 81	6 Bits
	0	Bit 82	1 Bit
	0	Bit 83	1 Bit
	Auxiliary Radiolocating Device	Bits 84 – 85	2 Bits
BCH-1	21-BIT BCH Code	Bits 86 – 106	21 Bits
Non- Protected Data Field	Emergency Flag	Bit 107	1 Bit
	Activation Code	Bit 108	1 Bit
	Emergency Code or National Use	Bits 109 – 112	4 Bits

 

EXAMPLES OF 406 MHz BEACON CODES

Maritime User Protocol with MMSI

Bit Field Name	Content	Bit Field	Bits
Message Format:	Short Message	25	0
Protocol Flag:	User Protocol	26	1
Country Code:	257 Norway	27-36	0100000001
User Protocol Type:	Maritime	37-39	010
Trailing 6 digits of the Ship Station Identity (modified-Baudot code):	743921	40-75	011100001010010000 000011011001011101
Specific EPIRB:	2	76-81	011001
Spare	Not Used	82-83	00
Radio-locating:	121.5 MHz	84-85	01
BCH-1:	21-bit BCH Code	86-106	101001011011010101000
Emergency Code Flag:	Bits 109 – 112 for National Use	107	0
Beacon Activation:	Manual Only	108	0
Emergency/National Code or National use data:	Not Used (Default Values)	109-112	0000

Beacon 15 Hex ID (bits 26 to 85): A029C 2900D 97591
406 MSG (Short) (bits 25 to 112): 5014E 14806 CBAC8 D2DAA 00

 

The list of beacon message protocols is depicted below. Click on the protocol of interest for additional information.

 

 

Cospas-Sarsat 406 MHz distress beacons are provided in models which transmit either a “short” distress message or a “long” distress message as indicated below. 406-MHz beacon messages are comprised of:

• a message preamble which is the combination of the 160 ms of unmodulated carrier, the bit synchronization pattern and the frame synchronization pattern,
• various other data fields which provide a unique beacon identification and, depending on the protocol used, other information that would be useful to Search and Rescue Authorities.

Note that additional information describing the beacon message characteristics of the fields is provided by clicking on the appropriate section of the message format diagrams below, or via the menu on the right-hand column of this page.

Fields of the Short Message Format

	Unmodulated Carrier (160ms)
Bit Synch	Bit Synch Pattern	Bits 1 – 15	15 Bits
Frame Synch	Frame Synch Pattern	Bits 16 – 24	9 Bits
First Protected Data Field	Format Flag	Bit 25	1 Bit
	Protocol Flag	Bit 26	1 Bit
	Country Code	Bits 27 – 36	10 Bits
	Identification	Bits 37 – 85	49 Bits
BCH-1	21-BIT BCH Code	Bits 86 – 106	21 Bits
Non- Protected Data Field	Emergency Code or National Use	Bits 107, 108, 109 – 112	6 Bits

 

Fields of the Long Message Format

	Unmodulated Carrier (160ms)
Bit Synch	Bit Synch Pattern	Bits 1 – 15	15 Bits
Frame Synch	Frame Synch Pattern	Bits 16 – 24	9 Bits
First Protected Data Field	Format Flag	Bit 25	1 Bit
	Protocol Flag	Bit 26	1 Bit
	Country Code	Bits 27 – 36	10 Bits
	Identification	Bits 37 – 85	49 Bits
BCH-1	21-BIT BCH Code	Bits 86 – 106	21 Bits
Second Protected Data Field	Supplementary and Position or National Use Data	Bits 107, 108, 109 – 132	26 Bits
BCH-2	12-BIT BCH Code	Bits 133 – 144	12 Bits

You have selected the Serial User Protocol to be coded with a beacon serial number identification. An interactive diagram depicting the information which should be coded into the beacon is provided below. Click on the hyperlinked fields of the diagram for additional information concerning the format, structure and content of the coding for that field.

 

Final Step: Register your beacon.

Having purchased and coded your beacon, one of the most important actions that you must take to maximize its effectiveness is to register the beacon with the appropriate national authority.  Registering your beacon provides search and rescue authorities with access to vital information (e.g. telephone numbers for emergency points of contact, type of aircraft, etc.) that is absolutely critical for efficiently conducting any search and rescue operation.

For further details concerning beacons refer to the following documents (available for downloading)

• C/S T.001, Specification for Cospas-Sarsat 406 MHz Distress Beacons;
• C/S G.005, Cospas-Sarsat Guidelines on 406 MHz Beacon Coding, Registration and Type Approval.

So far you have confirmed that your distress beacon will be used as a personal locator beacon and that it is a non-location protocol beacon. There is only one coding option that is suitable for this type of beacon. Nevertheless, you should contact your country’s designated authority to confirm that PLBs are authorised for use in your country (additional information concerning the authority/responsibility of States in respect of beacon message protocol selection is described at step 1 of this tutorial).

Click here for guidance in coding a PLB with the Serial User Protocol.

Return to Beacon Coding Tutorial Flow Chart

The final step in coding 406 MHz beacons is registering the beacon with the appropriate national authorities. In accordance with IMO and ICAO requirements national authorities should provide facilities for making this data available to Search and Rescue (SAR) services on a 24-hr basis. The extremely important step of registering your beacon is required to enable the proper SAR response if the beacon is activated. A list of points of contact responsible for beacon matters in countries throughout the world is available under the “Beacon Registration Contact Information” section of our website.

The Cospas-Sarsat Secretariat operates the International 406 MHz Beacon Registration Databse (IBRD) located at www.406registration.com. National authorities from some countries allow use of the IBRD for registration of beacons with their country codes. Beacon registration can only be accomplished using the online interface of the IBRD.

Why Register Your 406 MHz Beacon?

When a 406 MHz beacon is detected by the Cospas-Sarsat System, one of the initial actions taken by SAR services is to try and contact the owner of the beacon, or an emergency point of contact designated by the beacon owner, to confirm the nature of the distress event. Typically the following steps are followed:

The following scenarios highlight the importance of registering 406 MHz beacons:

You have selected the National Location Protocol to code your PLB. An interactive diagram of this option, depicting the information which should be coded into the beacon is provided below. Click on the hyperlinked fields of the diagram for additional information concerning the format, structure and content of the coding for that field.

Final Step: Register your beacon.

Having purchased and coded your beacon, one of the most important actions that you must take to maximize its effectiveness is to register the beacon with the appropriate national authority. Click here for details regarding the organizations responsible for beacon registration in your country (Pro/Contact Lists/406 MHz Beacon Registers). Registering your beacon provides search and rescue authorities with access to vital information (e.g. telephone numbers for emergency points of contact, type of aircraft, etc.) that is absolutely critical for efficiently conducting any search and rescue operation.

For further details concerning beacons refer to the following documents (available for downloading):

• C/S T.001, Specification for Cospas-Sarsat 406 MHz Distress Beacons;
• C/S G.005, Cospas-Sarsat Guidelines on 406 MHz Beacon Coding, Registration and Type Approval.

You have selected the Standard Location Protocol to code your PLB. An interactive diagram depicting the information which should be coded into the beacon is provided below. Click on the hyperlinked fields of the diagram for additional information concerning the format, structure and content of the coding for that field.

 

Final Step: Register your beacon.

Having purchased and coded your beacon, one of the most important actions that you must take to maximize its effectiveness is to register the beacon with the appropriate national authority. Click here for details regarding the organizations responsible for beacon registration in your country (Pro/Contact Lists/406 MHz Beacon Registers). Registering your beacon provides search and rescue authorities with access to vital information (e.g. telephone numbers for emergency points of contact, type of aircraft, etc.) that is absolutely critical for efficiently conducting any search and rescue operation.

For further details concerning beacons refer to the following documents (available for downloading):

• C/S T.001, Specification for Cospas-Sarsat 406 MHz Distress Beacons;
• C/S G.005, Cospas-Sarsat Guidelines on 406 MHz Beacon Coding, Registration and Type Approval.