When/how mapping happens

Vint Cerf vint at google.com
Fri Mar 27 22:41:04 CET 2009

The side-effect may be to reduce the motivation to move to the idna2008 rules. Let's see what others have to say. V

----- Original Message -----
From: idna-update-bounces at alvestrand.no <idna-update-bounces at alvestrand.no>
To: idna-update at alvestrand.no <idna-update at alvestrand.no>
Sent: Fri Mar 27 12:36:36 2009
Subject: RE: When/how mapping happens

Vince mentioned:
> The current protocol spec has an appendix in which a two-lookup method
> is suggested. If an non-mapping look up fails, then the IDNA2003-like
> mapping function would be applied and another look up attempted. there
> are other possible implementations, of course.

I would prefer that mapping be applied first (if desired), then lookup.  My reasoning is:

* There should be no mapping that maps a valid label to a different label. (In other words, my suggestion should have no net impact)

* If mapping is permitted to happen first, then applications can get away with one lookup, otherwise they have to try two lookups, which is harder at some layers.

* And, of course :), I'd like to reduce the steps in my implementation as much as possible, so this would help me.

I do not mean to give any more weight to the mapping step by this suggestion, I just hope to streamline implimentations.

- Shawn

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