Just speculating...
Chances are it is getting responses from all cards first if they are
compatible to a certain degree, later discarding invalid ones. If there
is some challenge-response process going on, the gate may still wait
for responses of the invalid cards, which they cannot answer correctly,
thus creating a little delay. Plus I would guess that the medium does
not allow very fast communication, so you may end up with 1 or 2
seconds lag until all messages of all cards are communicated, timeouts
etc., probably serially or even simplex.
Solutions would be to make your card scheme proprietary and not based
on standards, so only your own cards will work with your readers (I
believe Sony has made some changes to the standard, not the least to
provide a "customer lock in" feature but I don't know details). Or
better, deploy some sort of resolution protocol (e.g. only process data
from first completed protocol exchange, ignore all other
communications).
An interesting experiment would be to enter two or more valid cards for
the system (this case Suica) and see which one is charged and if there
is lag etc. But there will surely be a resolution protocol.
Otherwise make sure you only present only one card to the reader.
Dirk
On Wednesday, Oct 29, 2003, at 02:09 Asia/Tokyo, Ken Chang wrote:
> does anyone know when you have a number of IC cards within the range,
> how the technology will guarantee that the station communicate with
> and only with the wanted one?
>
> the JR gates sometimes have problem to access my Suica card, wasting
> me a second or two when I have other IC cards in the wallet.
>
>
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Received on Wed Oct 29 03:03:48 2003