Use MD5 or SHA256 checksums provided by the OEM. One bit flip can ruin the update.
If you are uploading a firmware file manually, always use an Ethernet cable rather than Wi-Fi to ensure the data transfer isn't interrupted. 844g1 firmware update top
Check the current version against the latest release notes in the Calix Community Portal (requires a professional login). Use MD5 or SHA256 checksums provided by the OEM