Editing Singulation (section)

== Tree walking ==
[[Image:RFID_search_environment.png|thumb|Tree walking singulation]] There are different methods of singulation, but the most common is ''tree walking'', which involves asking all tags with a serial number that starts with, for instance, a 0 to respond. If more than one responds, the reader might ask for all tags with a serial number that starts with 01 to respond, and then 010. It keeps refining the qualifier until only one tag responds. Note that if the reader has some idea of what tags it wishes to interrogate, it can considerably optimise the search order. For example with some designs of tags, if a reader already suspects certain tags to be present then those tags can be instructed to remain silent, then tree walking can proceed without interference from these.{{citation needed|date=December 2024}}

This simple protocol leaks considerable information because anyone able to eavesdrop on the tag reader alone may be able to determine all but the last bit of a tag's serial number. Thus a tag can be (largely) identified so long as the reader's signal is receivable, which is usually possible at much greater distance than simply reading a tag directly. Because of privacy and security concerns related to this, the [[Auto-ID Labs]] have developed two more advanced singulation protocols, called Class 0 UHF and Class 1 UHF, which are intended to be resistant to these sorts of attacks.{{cn|date=June 2022}} These protocols, which are based on tree-walking but include other elements, have a performance of up to 1000 tags per second.

The tree walking protocol may be blocked or partially blocked by [[RSA Security]]'s [[RSA blocker tag|blocker tag]]s.