Re: [RRG] Text proposal: mapping granularity

[Scott Brim <swb@employees.org>]

Excerpts from Tony Li on Thu, Mar 20, 2008 06:35:18PM -0700:
> 3.1.1.  Granularity
> 
>    The granularity of the mapping function controls the specificity of
>    the entries that make up the map.  Mapping large blocks of
>    identifiers to a common set of locators is highly efficient because
>    it reduces the amount of information needed in the mapping function,
>    but it sacrifices the ability for the mapping function to support
>    more specific information, at the expense of scalability.  

There's some subtlety missing.  "Information in the mapping function"
refers to state in mapping originators, the distribution system,
intermediaries ("holders"), and mapping points.  

Two-phase mapping functions (like ALT) can provide a high degree of
specificity at the mapping points while requiring very little state in
the distribution system or at holders, while at mapping points only
the information that is used is stored.

I think the best solution is just to delete the text above.  You don't
need it anyway, since what follows ...

>    Shifting
>    the scalability problem from today's routing protocols and forwarding
>    plane to tomorrow's mapping function simply moves the problem.  Thus,
>    any mapping solution that is going to have detailed granularity must
>    also have commensurate scaling properties.

... captures the requirement anyway.


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