IEC PAS 61162:2003 pdf download Maritime navigation and radiocommunication equipment and systems — Digital interfaces — Part 101: Single talker and multiple listeners — Modified sentences and requirements for IEC 61162-1
These sentences start with the “I” delimiter. The function of this special-purpose sentencestructure is to provide a means to convey information, when the specific data content isunknown or greater information bandwidth is needed.This is similar to a modem thattransfers information without knowing how the information is to be decoded or interpreted.The basic rules for encapsulation sentence structures are:
a) The sentence begins with the “!” delimiter.
b) Only approved sentence formatters are allowed.Formatters used by conventionalparametric sentences can not be reused.
c) Only valid characters are allowed.
d) Only approved field types are allowed)
e) Only Six bit coding may be used to create encapsulated data fields.
f) Encapsulated data fields may consist of any number of parameters, and their content isnot identified or described by this standard.
g) The sentence must be defined with one encapsulated data field and any number ofparametric data fields separated by the “” data field delimiter. The encapsulated datafield shall always be the second to last data field in the sentence, not counting thechecksum fieldh)
h) The sentence contains a“Total Number Of Sentences” field.
i) The sentence contains a “Sentence Number” field.
j) The sentence contains a “Sequential Message ldentifier” field.
k) The sentence contains a “Fill Bits” field immediately following the encapsulated data field.The Fill Bits field shall always be the last data field in the sentence, not counting thechecksum field.
NOTE This method of conveying information is to be used only when absolutely necessary, and will only beconsldered when one or both of two conditlons are true, and when there is no alternatlve.Condition 1: The data paramelers are unknown by devices having to convey the information. For example, theABM and BBM sentences meet this conditlon, because the content is not known to the Universal Automaticdentification System (AlS]transponder.
Condltion 2: When informatlon requlres a 8ignificantly higher data rate than can be achieved by the iEC 61162-1(4 800 baud) and IEC 61162-2 (38 400 baud) standards utilising parametric sentences.By encapsulating a large amount of informatlon, the number of overhead characters, such as “” fleld delimiters canbe reduced,resulting in higher data transfer rates. it is very unusual for this second condition to be fulfilled. As anexample, a UAlS transponder has a data rate capability of 4 500 messages per minute, and satisfies this condition.resulting in the vDM and VDO sentences
Data format protocol
Reference lEC 61162-1 Section 5: New section 5.3.7 multi-sentence messages, see also 4.1and 42 below
Multisentence messages may be transmitted where a data message exceeds the availablecharacter space in a single sentence. The key fields supporting the multi-sentence messagecapability shall alwavs be included. without exception, The required fields are: total numbeof sentences, sentence number, and sequential message identifier fields. Only sentencedefinitions containing these flelds may be used to form messages. The TUT sentence is agood example of how a sentence is defined to provide these capabilities.
The Listener should be aware that a multi-sentence message may be interrupted by a higherpriority message such as an alarm sentence, and thus the original message should bediscarded as incomplete and has to await re-transmission. The Listener has to check thatmulti-sentences are contiquous.