Re: Disabling RFID by mains force

["Dave Howe" <[EMAIL PROTECTED]>]

Stefek Zaba wrote:
> On Fri, Oct 31, 2003 at 07:01:45PM -0000, Dave Howe wrote:
>>> Actually there are protocols that can count the number of items
>>> being scanned at any one point in time, even when these have the
>>> same ID. 
>> Interesting - do you have any online references?
> www.rfid.org is an obvious place to start, while the RSALabs paper
> on selective blocking gives a good description of the "individuation"
> protocol.
> The tags cooperate in a recursive-descent enumeration. Roughly, the
> reader says "first bit 0?" and all tags with first-bit-0 speak up
> with their second bit. If the reader hears responses implying the
> presence of tags with both "00" and "01" prefixes, it recurses down
> both branches of the tree; if it hears a response from only one
> subbranch, it recurses down only that branch. This way, it gets the
> uniqIDs of all responding tags in a number of steps bounded above by
> <number-of-tags-present> times <bitlength-of-a-tag-ID>,
surely that requires that they *have* a unique ID - not all the same?