Re: Arbitrary-length numbers
2011.05.27 петък 19:42:09 Russ Allbery:
> "Тони Стоев | Toni Stoev" <debian@tonistoev.info> writes:
>
> > Why so, what is the gain? A promising example: use of arbitrary-length
> > numbers in network addresses. Node addresses can be adequate in size to
> > fit local needs, not squeezing the universal expansion of the network.
>
> Just to add a bit to what Ian said, please note that methods of writing
> down arbitrary-length numbers in binary are well-understood and have been
> well-understood for quite some time. Lack of an algorithm is not why
> network addresses use fixed-width fields. Rather, the problem is that
> arbitrary-length numbers are much slower because you don't know exactly
> how long the packet header is going to be and therefore cannot write
> highly-optimized software (generally accompanied by highly-optimized
> hardware) for routing packets when you use variable-length packet headers.
> The performance penalty would be prohibitive for Internet routers.
Unless numbers and the header are processed at the very moment they come in, properly like with hashing.
This is greatly a matter of hardware. But as a beginning the software can lead the way.
Furthermore, network packet processing depends on protocol layering. Here is the solution to that:
Role-Based Architecture: http://isi.edu/newarch/DOCUMENTS/hotrba.paper.pdf
Processing packets based on functions dynamically identified in header.
> This was a topic of considerable discussion during the IPv6 design, since
> of course everyone would have preferred to use arbitrary-length addresses
> had it been possible.
Not enough decision makers could have imagined possible the depth and generality of the solutions we are discussing with you.
> --
> Russ Allbery (rra@debian.org) <http://www.eyrie.org/~eagle/>
>
>
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