The term “class” was used by the original Auto-ID Center to differentiate among the capabilities of different types of tags. Here is a breakdown of the classes as originally proposed.
• Class 1: a simple, passive, read-only backscatter tag with one-time, field-programmable non-volatile memory
• Class 2: a passive backscatter tag with up to 65 kilobytes of read-write memory
• Class 3: a semi-passive backscatter tag with up to 65 kilobytes of read memory (essentially, a Class 2 tag with a built-in battery to support increased read range)
• Class 4: an active tag that employs a built-in battery to run the microchip’s circuitry, and to power a transmitter that broadcasts a signal to an interrogator
• Class 5: an active RFID tag that can communicate with other Class 5 tags and/or other devices (essentially, tags that can form ad hoc mesh networks)
This system was never really adopted by GS1 when it created the Electronic Product Code (EPC) standard, however. Though passive ultrahigh-frequency (UHF) EPC transponders are sometimes referred to as Class 1 Gen 2, in reality, there is no Class 1. So a Class 1 battery-assisted passive (BAP) tag would have been considered a Class 3 tag under the original classification proposed by the Auto-ID Center. Currently, it is referred to as a Class 1 BAP tag, simply because it utilizes the same transponder as a passive UHF system, based on the EPC air-interface protocol standard.
The bottom line: There are no classes of EPC tags, and an EPC BAP tag is one that uses a battery to power a sensor, but communicates with a reader in the same way that a passive EPC transponder does.
—Mark Roberti, Founder and Editor, RFID Journal
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