On Sun, 9 Jan 2005 09:54:02 +0000, Phil Richards
wrote:

I'd disagree to say it's on the account with the card being the device to
use to access the account.

Not that I'm aware of. Contacting a central computer before[1]
opening a set of barriers would be too slow, and on a bus would be
difficult and costly (you'd need a high-speed, 100% coverage and
high-reliability radio data network covering all of TfL Buses'
operating area for a start).

One of the ideas of "smart cards" is that they can, with relative
security, store actual value on the card. This may well, for security
reasons[2], be shared with the "shore" systems, but is not the primary
storage, and doesn't have to take place in real time.

While I don't know what kind of connection the barriers have with
"Oyster central control" (for want of a better term) it'd need to be a
decently quick and permanently online one for online validation (and
you know how long that tends to take for credit cards - can you
imagine that delay at a ticket barrier?), but for batch communication
it could be a 14k4 modem online for half an hour every night[3].

The above is the reason why, when you credit a pre-pay card, you must
nominate a specific railway station (not a bus!) to load the card with
the credited value - because it needs to be transferred to that
station to tell it to credit the card.

[1] I don't think it would be sensible to "trust" the card and update
the account later on, because this could lead to widespread fraud once
people noticed you could get away with it.

[2] so a duplicate can be issued in the event of loss (I think they do
that), and also to prevent anyone who can circumvent the security on
the card from adding value to it without getting caught.

[3] I know this is unlikely, but the point is that real-time
transactions involving that amount of data use a lot of bandwidth,
while batch transactions don't.

The same as say your bank card is used to access
funds in your bank account. If my bank want to refund me 20p they owe me, I
don't have to go to my local branch with my switch card, it can all be done
over the phone.

The difference is, as stated above, that the card is the primary
value-holding device for Oyster, as it is for the stored-value
magstripe tickets you get in some cities outside the UK, or even for
simple technologies like Clippercards or Bus Savers where the stored
value is a physical bit of paper.

It would not be feasible, or even desirable, to make a card the
primary means of storage for a bank account - though schemes do exist
like the German Geldkarte scheme whereby you can store a small
"electronic purse" on a smart card - just like Oyster Pre-Pay!

Neil

--
Neil Williams in Milton Keynes, UK
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