Protocol scope and method
The common header is interpreted as big-endian length, serial, message ID, platform center ID, three version bytes, encryption flag and key.
4 + 4 + 2 + 4 + 3 + 1 + 4 = 22 header bytes.
Diagnostic scenario
Extract an unescaped 22-byte common header from a redacted inter-platform packet. Compare declared length, serial, message ID, center ID, version bytes and encryption fields with both peer logs before selecting a body decoder.
How to interpret the result
The common header is big-endian and identifies the profile needed for later handling. A plausible message ID does not compensate for a wrong total length or encryption assumption. Encrypted body content cannot be interpreted from the header alone.
Input reference
- Unescaped 22-byte header
- Example default: Sample input included
Common mistakes
- Using an unredacted production capture with vehicle, credential or network identifiers.
- Applying terminal-protocol byte order to an inter-platform 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.
- Compare the full 22-byte header and total length with both peers.
- Keep a redacted known-good and known-bad sample as a regression pair.
Questions to check during diagnosis
Does the JT/T 809 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.