Technology
Clipper utilizes a NXP Semiconductors MIFARE DESFire (MF3ICD40) integrated circuit to manufacture the card. The card operates on the 13.56 MHz range putting it into the Near Field Communication category (rather than RFID, as is commonly misconceived). Because the card uses NFC technology, any NFC enabled Android cellphone can read the serial number, travel history, and current balance on the card. However, data cannot be written to the card without the proper encryption key, preventing unauthorized access to funds on the card. The former Translink cards, while still functional on the fare system readers, do not conform for MIFARE and are unreadable by 13.56 MHz readers.
Because Clipper operates in multiple geographical areas with sporadic or non-existent internet access, the fare collection and verification technology needs to operate without any networking. To accomplish this, the Clipper card memory keeps track of balance on the card, fares paid, and trip history. Unfortunately, this also means if funds are added to the Clipper account via the internet, funds will not show up on the clipper card until it has been scanned at an internet-enabled (or recently synchronized) device. Buses and other vehicles without internet access will have to return to a service station in order to synchronize with Clipper's servers. During synchronization, the payment collection device will upload to the server data about any fares collected, and will download information about new account balances. Riders who scan their card at a recently synchronized payment collection device will have their card updated to reflect their true account balance.
The waiting period between synchronizations may cause some cards to report lower funds than what is actually on its corresponding Clipper account. In order to alleviate this problem, Clipper allows riders to go up to -$11.25 on the card before funds need to be added, and/or the card needs to be scanned at an internet-enabled or recently synchronized device.
Read more about this topic: Clipper Card
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