When the Auto-ID Center at the Massachusetts Institute of Technology (MIT) proposed a structure for tracking goods in the supply chain with radio frequency identification tags carrying Electronic Product Codes (EPCs), it proposed having five classes of tags.
Class 1 tags would be passive ultrahigh-frequency (UHF) transponders that could be written to once and then be read many times (WORM). Class 2 tags would be read-write and feature user memory. Class 3 tags would be semi-passive tags, suitable for use with sensors. Class 4 tags would be active tags. And class 5 tags would be RFID tags with onboard computing power that could form mesh networks and communicate with each other.
This classification of tags based on functionality never really took off. One reason is that EPCglobal has yet to create a standard for any tags other than passive UHF tags. So the vision of interoperable tags of different classes has not been realized. It might still happen, but it seems more likely that active tags will be based on the ISO 18000-7 standard, and will not be interoperable with passive tags based on EPCglobal’s standards.
—Mark Roberti, Editor, RFID Journal
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