Compressed Item Report Frames

A compressed item report frame has a payload of between 20 and 24 bytes.

Callsign	SSID, Path Code & Data Type Code	Compressed Data
4 bytes	1 byte	15—19 bytes
CCCC	D	/XXXXYYYY$csTttt(tttt)

where:

• CCCC: 4 bytes for the compressed 6 character Callsign

• D: compresses into 1 byte:

  • the SSID (between SSID 0 [none] and 15; included),

  • the Path Code (between path 0 [none] and 3; included), and

  • the Data Type Code = 2

• /: the Symbol Table Identifier

• XXXX: the Base91 compressed longitude

• YYYY: the Base91 compressed latitude

• $: the Symbol Code

• cs: the compressed course and speed

• ttt(tttt): 3 to 7 bytes for the compressed Item Name (between 3 and 9 characters of the limited 42 character set)

Notes:

• The i‑gate adds the Compression Type Byte T right behind cs.

• The parenthesis are not sent; these merely indicate optionality.