—Salman (Tsukuba, Japan)
Some ultrahigh-frequency (UHF) EPC tags have a tag ID and some do not. The tag ID is a serial number created at the time that the microchip is produced at a manufacturing facility. It is the serial number that differentiates one microchip from others.
The Electronic Product Code is written into a tag at the plant for read-only tags, but it is more common today to buy read-write tags and write the EPC to the tag yourself. UHF readers based on the EPC standards read the EPC, but can also be set up to read the tag ID. This is most often used to authenticate the tag and item. A criminal could purchase blank EPC transponders, write legitimate serial numbers to the tags and then place those tags on counterfeit items. If a company knows the tag IDs and matches them to the EPCs, however, then this is impossible.
As for your second question, when an EPC tag is read, the interrogator passes the EPC (not the tag ID, unless you set up the system to do that), the reader ID and a timestamp. The reader can usually be set up to tell you which of its antennas read the tag. This is important if you are using the same reader to power four antennas, and those antennas are covering different dock doors.
The EPC is divided into a header, a manager number that defines the company that made the product, and an object class that defines the product. Then there is a serial number. EPCglobal has set up the Object Naming Service (ONS), designed to enable businesses to quickly look up who made a particular item, as well as what that item is. In most cases, I believe companies manage this information internally. That is, a retailer knows the manager numbers for its partners and adds the object class for each product in its master file of products it buys. When a tag is read, it can look up internally what that product is.
—Mark Roberti, Editor, RFID Journal
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