Bit Message
The Bit Message is a message that is hidden within the lines of an octet stream and it is represented as a hexadecimal string which has maximum length of 149 octets. The first 9 octets of the message contain the header for the message and the rest comprise the content. The header contains 1 type octet, 7 timestamp octets, and 1 message length octet. The content contains a maximum of 140 octets and could be packed with either 7 bit, 8 bit or 16 bit. 7 bit packed messages have a length of 160 characters, 8 bit packed messages have a length of 140 characters, and 16 bit packed messages will only have a length of 70 characters.
Here are some details on the structure of a bit message:
| BIT MESSAGE FORMAT | ||||||||||
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | ||
| Octet-nth | ||||||||||
| HEADER | TYPE | |||||||||
| YEAR | ||||||||||
| MONTH | ||||||||||
| DAY | ||||||||||
| HOUR | ||||||||||
| MINUTE | ||||||||||
| SECOND | ||||||||||
| TIMEZONE | ||||||||||
| LENGTH | ||||||||||
| CONTENT | Octet-1 | |||||||||
| ... |
... |
|||||||||
| Octet-140 | ||||||||||
| 7-BIT PACKED MESSAGE | ||||||||||
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | ||
| Octet-nth | ||||||||||
| 1 | 0 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | ||
| 8-BIT PACKED MESSAGE | ||||||||||
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | ||
| Octet-nth | ||||||||||
| 1 | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | ||
| 16-BIT PACKED MESSAGE | ||||||||||
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | ||
| Octet-nth | ||||||||||
| 1 | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | ||
| 2 | b15 | b14 | b13 | b12 | b11 | b10 | b9 | b8 | ||
| HEADER | # OCTET | DESCRIPTION | |||||
| TYPE | 1 | contains specific flag for specific format identifier | |||||
| DETAIL | |||||||
| Bit 0-1 : | reserved message class meaning | ||||||
| Bit 2-3 : | message encoding | ||||||
| Bit 3 | Bit 2 | Pack | |||||
| 0 | 0 | 7 bit | |||||
| 0 | 1 | 8 bit | |||||
| 1 | 0 | 16 bit | |||||
| 1 | 1 | reserved | |||||
| Bit 4 : | reserved flag message class meaning | ||||||
| Bit 5 : | reserved message is compressed or uncompressed | ||||||
| Bit 6-7 : | reserved general data coding | ||||||
| TIMESTAMP | 7 | contains specific swapped nibbles for specific format identifier | |||||
| DETAIL | |||||||
| Octet 1 | YEARe.g. 10 for 2001 | ||||||
| Octet 2 | MONTHe.g. 10 for Jan | ||||||
| Octet 3 | DAYe.g. 10 for 01 | ||||||
| Octet 4 | HOURe.g. 10 for 01 | ||||||
| Octet 5 | MINUTEe.g. 10 for 01 | ||||||
| Octet 6 | SECONDe.g. 10 for 01 | ||||||
| Octet 7 | TIMEZONEe.g. 80 for 08 x 15 / 60 = +2 | ||||||
| The Time Zone is GMT format, expressed in quarters of an hour. In the first of the two semi-octets, the first bit represents the algebraic sign of this... | |||||||
| LENGTH | 1 | maximum characters allowed is 160, 140 or 70 characters depends on message packed format | |||||
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