3 ms·
IIRC Japan's FeliCa (Suica, PASMO, etc.) is much faster because it had more stringent timing requirements in the spec because of how many people they needed to
by cbhl 5y ago
IIRC Japan's FeliCa (Suica, PASMO, etc.) is much faster because it had more stringent timing requirements in the spec because of how many people they needed to be able to walk through a turnstile, which increases the cost of the associated hardware (the readers in the turnstiles/trains/buses, as well as in e.g. iPhone chips).
IIRC Presto does store the value on the card -- when you load value online, every bus/train/turnstile gets a batch data file of cards it needs to update the balance for, and checks every card that passes through it to see if yours is one of them, and then writes the updated balance to the card. But the slower scans are due to the choice of a different standardized transit pass format (one that allows for much slower -- IIRC, hundreds of ms -- reads/writes than the Japanese standard).
- julianlam 5y agoThanks for the explanation! I didn't know Presto stored that kind of data on the card and assumed otherwise given the lag time. I stand corrected!
- bellyfullofbac 5y agoFor the Japanese cards, there are Android apps that can read the last several transactions using the phone's NFC chip, so there's obviously local storage there too. Although my guess is there's redundancy with online data to ensure there's no shenanigans. The cards also work on other things, like the many vending machines in Japan, I wonder if they're all online. Maybe the protocol is designed that subtractions are easy but additions are hard...
- frosted-flakes 5y agoThe Presto app also does that, and you can top-up the card by tapping your phone's NFC reader as well.