Esszett, Final Sigma, ZWJ and ZWNJ

Paul Hoffman phoffman at imc.org
Tue Feb 24 02:54:23 CET 2009


At 8:14 PM -0500 2/23/09, Vint Cerf wrote:
>Mark,
>
>thanks - I think what left me in an ambiguous state was the term "bits on the wire".  In your example, under the IDNA2003 mapping process, the final sigma is mapped into ordinary sigma and THEN the resulting string is looked up (after conversion to xn-- format using the punycode algorithm). The two forms become identical prior to lookup.

Mostly right. To be clear: that's not the IDNA2003 "mapping process", it is the IDNA2003 protocol. The mapping part is not optional, nor really separable.

>Under the proposed IDNA2008 rules, the two strings remain distinct in both the U-label and A-label format and thus look "different" on the wire and unless other measures are taken (bundling, restricted registration, etc) it is possible for the two domains to yield distinct results on lookup.
>
>Paul - is that the picture you wanted to paint?

No, and the differences are important. Your last sentence should read:

Under the proposed IDNA2008 rules, the two strings remain distinct in both the U-label and A-label format and thus are different on the wire. Unless restrictions are made on the registrants of the different domain names, it is possible for the two domains to yield distinct results on lookup.

- They don't "look" different: they are different. That's why we are talking about bits-on-the-wire.

- Bundling doesn't prevent yielding different results: it just shifts the choice to make the results the same onto the registrant.

- Restricted registration doesn't prevent yielding different results: it just shifts the choice to make the results the same onto the registrant.


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