Need info on how FedEx,USPS,DHL tracking system works.

Any one who have or knows this stuff please help me. I need it for some documentation for my paper. I really appreciate your help.
Thanks.
Answer #1
depending on what class you choose to send mail
they scan it ever single time it changes a location, or hands of a worker.
(not sure about dhl)
Answer #2
The parcel has a unique barcode.
Every major movement of the parcel, it gets scanned and that scan is recorded in the database.
When you do a check it pulls the database list for your parcel number and shows it to you.
Parcels in transit just show the last recorded scan unless it maybe changes hands/trucks, then it gets scanned again.
When you sign for it your sig is recorded in the database and it’s logged as delivered.
This protects them and you from false delivery, etc.