Traffic locality and other questions
Sean M. Doran
smd at clock.org
Thu Sep 25 13:47:21 UTC 1997
Sean Donelan <SEAN at SDG.DRA.COM> writes:
> I have some questions whether it is better to aggregate traffic into
> a single huge flow, or if it is better to have lots of
> smaller paths.
Ah, good question.
What seems to scale better is aggregating things into
large buckets which are switched together rather than
merely filtering lots of small individually-switched
buckets of data through single pieces of equipment.
There are some assumptions driving this. Firstly, it is
easier to move large numbers of symbols per second than it
is to make large numbers of switching decisions.
Secondly, it is possible to build a hierarchical routing
scheme that can take advantage of aggregation
opportunities to put similar traffic into big buckets
along particular path segments. Thirdly, there are
economies of scale which can be exploited when one uses
large data pipes that reduce the cost of moving traffic
If all of these assumptions prove to be invalid, and in
particular if it is cheaper to build equipment which are
better at switching very small amounts of data across many
diverse physical paths, if a routing scheme that can fully
exploit this can be developed, and if it is more
economical to use many small pipes than a few large pipes,
then obviously one would be better off not aggregating
traffic, and perhaps even deaggregating it and its
complementary reachability information.
> BGP isn't very good at showing 'other' transit paths to
BGP is a distance vector protocol and not a map-exchanging
protocol. You cannot build a completely accurate map of
the Internet from a subset of BGP distance vectors.
BGP routers will also only announce their paths of choice
to their neighbours, and therefore any other paths they
may know will be hidden.
> What I find interesting is the rankings of traffic flows I see don't
> match with what the pundits rank as the largest network providers. I
> don't know what that means though.
I suppose it depends on what people describe when they say
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