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Comment by Ecco | Hacker News Reader

With a limit of 10 million different serial numbers, I wonder how China does it. I can't come up with a decent estimate, and maybe I'm way off. But with the growth of sellers like Shein or Temu, I wouldn't be surprised if they shipped that many parcels in like a single day ? Or at least in a timeframe short enough that they would have over 10 million shipped but yet-to-be-delivered parcels, effectively running out of tracking numbers.

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What helps is that they don’t ship direct from China by mail much. They often send in bulk to the destination country and then mail locally, and local post systems can have their own domestic format.

Or they have their own private courier do the last mile delivery too so it never touches any postal operator.

Do they? In Australia usually get them direct from HK or China because it is cheaper to do that even than post it within Australia!

In Southern Ontario Canada, yes, even in the suburbs, most stuff is dropped off by some rando courier for a few years now.

Somehow cheaper than paying bulk international airmail rates.

> With a limit of 10 million different serial numbers, I wonder how China does it.

The author has issued a correction, it's 100 million numbers per service indicator. But even then, it's probably not enough.

The boring answer is that your shipping options are either get untracked postal service (which the S10 standard does not apply) or use a private courier (which also does not use the S10 standard).

If you insist, you got two options for UPU-based postal tracking: normal e-commerce parcel aka H-codes, practically 2,300,000,000 trackable packages per year [1]. EMS is the other route, and there are another 2,300,000,000 trackable packages per year [2]. However, in my experience tracked postal delivery is only used in certain countries where it is more advantageous than private delivery (like until very recently in the US, for complicated reasons [3]), while other destinations has a more-than-willing private delivery partner (that is not the Big Three [4]) or even set up the delivery systems themselves.

1: 23 service indicators: HA-HW, HX-HZ are reserved for multilateral/bilateral use only

2: another 23 service indicators: EA-EW, EX-EZ are reserved for multilateral/bilateral use only

3: https://www.thewirechina.com/2020/11/22/delivering-chinas-ma...; https://www.ft.com/content/a1233f3e-d21a-11e8-a9f2-7574db66b...

4: DHL, FedEx, and UPS

Yeah. Apparently last year they shipped over two million small parcels to Finland (pop. 5.6M) alone, which is completely bollocks.

> completely bollocks

Do you mean “bonkers”? Because “bollocks” in this case would mean “made up”.

Oops, yes!

Service type and serial need to be unique. Countries control what that 2letter field means. There is no rule against multiple codes indicating the same service. So AA through AZ would give you 260,000,000 unique combinations that you shouldn’t reuse for 1 year. Rinse, later and repeat if you need more.

Is the serial number even in base 10? the other parts of the number allow letters, the article does not say, but it could easily be base 36. which is close to 3 trillion serials.

Plus a bonus rant: this is one of those things that looks like a number and as such you are tempted to use a number to store it, but its not, it's a string, you will never do math on it so it is not a number. see also: phone numbers, social security numbers, serial numbers.

and sheepish bonus update: there is a checksum, so math is done on it. wonder if the checksum makes more or less sense in base 36? probably less, the checksum almost looks base12-ish, the mod(11), but there are special cases for two digit values so it is probably base 10.

Eh, your comment here was checksummed several times as well crossing the network. Doesn't make it "a number".

You could hate it by an internal metric, like date received.

And I wonder what was the constraint to not make it longer when they developed the standard. Making it a few digits more seem it wouldn't cost much.

The cost will be in updating every legacy postal system that currently has fixed column lengths/input field length limits.

Yes, now, but the person you're replying to was asking about at inception.

Why was IPv4 so pitifully small? I guess most people thought 100 million parcels a year was a ridiculously generous limit that we'd never reach.

Even the US must easily run into this constraint.

The short answer is probably : in-house consolidation.

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