Appendix C: Sessions
Session is a concept of the EPC Global Standard to allow a tag to respond to multiple readers
inventorying it at the same time, each using a different session number.
There are 4 possible sessions: S0, S1, S2, S3.
The user however has to be careful because these 4 sessions have different behaviors, notably
how the tag flag “persists” in time. A tag, before being inventoried or when just after being
powered on, has a flag of State A. When it is inventoried, the flag will go to State B. The tag
flag will stay in State B until the tag powers off or the persistence time is up.
A reader can declare it only wants to inventory flag A, so that after a tag is inventoried and its
flag gone to State B, it will no longer respond to further inventory rounds – until the end of the
persistence time.
Now for S0, S1, S2 and S3, the persistence times are DIFFERENT! Because of that, one has to
be very careful in choosing which session to use.
Tag Energized: 0.5 second < Persistence Time < 5 seconds
Tag Not Energized: 0.5 second < Persistence Time < 5 seconds
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