Access Control & RFID

Access control deals in authorisation, not in door hardware. At every point the same three facts are looked up in a table: which identity, through which door, within which hours. What a card, an RFID tag or a phone carries is not a key but an identity number; the decision belongs to the field controller that finds that number in the authorisation table. A lock releasing is the result of that decision, never the decision itself.

Withdrawing an authorisation is the critical moment. Once a departing employee's record drops off the list, every reader that accepts that identity is expected to learn it within seconds. How controllers behave when the link to the server breaks is settled in advance too; the choice between working on from a local copy and holding the door shut is written down according to the nature of the site, rather than left as behaviour to be discovered later.

Staff, visitors, vehicles and assets share one table with different lifespans. A visitor record is bounded in hours and lapses of its own accord, while a contractor record is tied to the term of an agreement. Once a plate read by LPR becomes an identity record, the barrier recognises the vehicle instead of the driver. Where an RFID tag is fixed to material in transit, the door counts an asset rather than a person, and a warehouse exit turns into an access event.

Every read is stored with its point and its time, accepted or refused. Refused reads usually say more than accepted ones: an expired authorisation, a borrowed card or a wrongly defined shift window shows up here first. The rule that stops one identity entering twice without an exit read is the simplest check that makes card sharing visible. Matched against footage carrying the same timestamp, a read also shows who went through.