Re: [RRG] Providers and providers

[jnc@mercury.lcs.mit.edu (Noel Chiappa)]

    > From: David Conrad <drc@virtualized.org>

    >> Large corporations that have large networks are ISPs.

    > Please define 'large'.

Perhaps your question is a rhetorical device, and you're merely trying to
point out that how to define 'large company' is a tarpit. For those who
really do need a definition of 'large', here are some thoughts.


Go back to the graph theory, which is what's underneath all this routing
stuff. For purposes of path selection computations, you need to indentify
nodes (and maybe arcs too, depending on your exact algorithm) in the graph.
For small graphs, you just number all the nodes, you're done. If it's a
really, really, really big graph, though, you can't do resource-feasible
computations if all you have is numbers for each distinct node.

In a very large graph, for purposes of path selection computations, you need
to select and name 'chunks' of the graph, and do path selection computations
for source-chunk / destination-chunk pairs; then you do further computations
for paths inside the chunks (and recurse, if necessary).

How many chunks is 'enough' and how many is 'too many'? It all depends on
lots of factors (e.g. how much memory/processing/bandwidth overhead you want
your path computations to consume, how efficient you want the paths to be,
etc, etc).

Anyway, once you've decided how big your top-level 'chunks' are going to be,
a corporation whose network has that many nodes is 'large', and gets its own
top-level 'chunk' identifier (aka PI locators); companies smaller than that
do not.

Put it another way, if you decide the DFZ can handle E entries, and the
total size of the network is N nodes, if a company has more than N/E nodes,
it gets PI locators, and if it has less than N/E, it doesn't.

	Noel

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