In my experience....
The passages are a credit card sized item with a smart chip in it. The
chip handles a challenge/response protocol, so you can't just copy the
response and use it twice. The carrier takes the card, reads it and
validates it at boarding. This also burns into the chip that the
passenger boarded, and the name and ID info of the passenger.  Note
that most readers (which you'd use to copy the card) will also burn
the "boarded" tag when the chip runs it's computation, so fiddling
with it to try to make a copy tends to leave you with an unusable
card.

When the carrier stops at a C or above starport, and some D's, they
can turn the card over to the starport and get credits. This burns a
second usage code into the chip and marks it completed.

The starport also keeps a list of all the cards used, and sends the
list on the next X-boat to a clearing house. The clearing house does
some validation, and if all is okey-dokey, the next x-boat going back
to that starport drops off credits (digital form) to the appropriate
accounts.

When you buy a "open passage ticket" or when the agency mustering you
out issues you one, they transfer the credits into escrow with the
clearing house system.

Almost all clearing house handling is handled by a subsection of the
IISS X-boat network administration, pretty much in the same way as you
buy money orders at post offices. Interest on the money in escrow pays
for the administration.

Rumors that the IISS monitors where, when and by whom a passage is
used and shares this info with other elements of the Imperium abound,
but there's no proof of it.

On Fri, Dec 17, 2021 at 11:46 AM carlos.web at mail.de (via tml list)
<xxxxxx@simplelists.com> wrote:
>
> <lurk mode off>
> Something has been bothering me for a while in the basic Traveller setting, and as I slowly prepare to return to DMing Traveller/Cepheus after a long hiatus, I thought to turn to the collective wisdom here to see what I am missing.
>
> Mustering out benefits in the OTU and in other settings (Cepheus...) often yield High or Low Passages. But then I have two problems. First, what is exactly a High/Low Passage? It seems to be conceived of as some physical ticket that will be accepted by a generic trader in exchange for, well High or Low Passage for one jump, and that will last indefinitely until used. But how can that possibly work in a universe where the speed of travel is one week per jump? Say I have a High Passage, which is pressumably a long alphanumeric code or a crypto-ID. I give a copy to a friend, who travels to another world. When we are sufficiently apart, and within less than a week fro meach otehr, we BOTH use the passage. There is no way the unsuspecting traders will uncover that it is being used twice. The information that it has been used in point (a) will take weeks to travel to point (b), where it has already been (also) used. I am puzzled.
>
> Second, who exactly is guaranteeing these passages, and, most importantly, why? In the OTU one could handwave it as being "the Imperium," but why would the 3I want to take upon the enormous bother of keeping track of the spent/unspent passages? Or is it a decentralized form of providing perks, granted by all kinds of organizations and coordinated by a central organization like the TAS for a fee? The economics of this escapes me (disclaimer: I am an Economics professor and i might worry too much here). And in other universes without a large interstellar polity, who is granting them at all? How do you cope with this IYTU?
>
> Apologies if this has already been discussed/solved. I am a bit stumped.
>
> Carlos
> <lurk mode on>
>
> --
> Prof. Dr. Carlos Alós-Ferrer
> Department of Economics, University of Zurich
>
> Read some of my most-recent publications:
> - "Generous with Individuals and Selfish to The Masses," Nature Human Behavior 2021: https://rdcu.be/cqPad
> - "Time Will Tell: Recovering Preferences When Choices Are Noisy," Journal of Political Economy 2021: https://doi.org/10.1086/713732
>
>
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