Protocol scope and method
The body-property word controls body length, encryption, subpackaging and whether a protocol-version byte and expanded terminal ID are present.
bodyLength = attributes & 0x03ff; versionFlag = bit 14.
Diagnostic scenario
Extract the common header after removing frame delimiters, reversing escapes and excluding the checksum. Use the body-property word to decide whether the version byte, expanded terminal ID and subpackage fields are present before calculating the body offset.
How to interpret the result
The header length is conditional rather than fixed. If the version or subpackage bit is interpreted incorrectly, every later byte offset shifts while early fields can still look plausible. Header status should therefore be reviewed together with the calculated byte count.
Input reference
- Unescaped header hex
- Example default: Sample input included
Common mistakes
- Using an unredacted production capture with vehicle, credential or network identifiers.
- Assuming every message uses the legacy 12-byte common header.
- Treating a successfully parsed sample as standards compliance or interoperability proof.
Before using the result
- Confirm the protocol edition, transport framing and vendor profile before interpreting fields.
- Check version and subpackage bits before selecting the header length.
- Keep a redacted known-good and known-bad sample as a regression pair.
Questions to check during diagnosis
Does the JT/T 808 Header Decoder leave my browser?
No application upload is used. Avoid putting sensitive production data in shareable URLs.
Is this a standards compliance test?
No. Confirm the edition and vendor profile with licensed documents and your target platform.
Offline diagnostic aid. Verify fields, version and vendor extensions before production use.