IP: 100% per year, etc

[Dave Farber <farber () cis upenn edu>]

> Date: Tue, 28 Nov 2000 06:26:22 -0500 (EST)
> From: mo () UU NET (Mike O'Dell)
> To: farber () cis upenn edu
> Subject: 100% per year, etc



> Dave,
>
> I see people still don't really understand the difference
> between offered load (measured as gigabits injected into
> the edge of the network) and network capacity (measured in
> gigabit-route-miles of trunking).
>
> This is indeed somewhat subtle and possibly counter-intuitive.
>
> For offered load to double every year, network capacity
> must double every 4 months or so, at least in our network
> (UUNET).  It is slowing down a some, but that's still pretty fast.
>
> This is actually a pretty simple result from graph theory,
> once one gets the picture right (as are most results
> from graph theory - grin).
>
> I admit it took me a while to get the picture right,
> especially about how to explain what's going on.
>
> Consider an network of two nodes connected by one mile
> of fiber.
>
> In this network, it's pretty clear that the number of
> gigabits of offered load should be equal to the number of
> gigabit-miles of trunking between the two nodes.
>
> Note that it's only the NUMBERS that are equal - the UNITS
> of the numbers are different.  One is gigabits/sec, the
> other is (gigabits/sec)*miles.  This means they can never
> be *equal*, but the two numbers can grow together - maybe
> even related by a constant of 1 mile, as in this case.
>
> Now consider a real network.
>
> The network is much more complex than two nodes with one
> link, and each of those nodes is generating traffic which
> can go to any arbitrary destination node on a
> packet-by-packet basis.
>
> In North America alone, there are "35 NFL Cities" which
> account for a significant fraction of the population
> (people or computers, take your pick), but there are also
> many more computers located other places who also wish to
> have high-performance service.  This means the trunking
> must go a lot of places and be richly connected because...
>
> Every computer expects to reach every other computer with
> nearly equal quality.  While Warhole's Theorem is still
> relevant, on the Internet you are famous for 15 milliseconds,
> so who is famous changes very quickly.
>
> The resulting traffic slosh can be very large and the
> network trunking capacity (gigabit-route-miles) better
> be in place to handle it or Bad Things(TM) happen.
>
> The result is that for UUNET's network (I can't speak for
> others) to handle the 100% increase in gigabit/sec offered
> load over 12 months, the gigabits/sec-route-miles capacity
> of the network must increase 100% about every 4 months.
> Again, note the difference in the units of those two
> numbers.
>
> The planning problem for telephony networks is rather different
> because the dynamics of telephone calls are so much slower
> and the data rate required is perfectly predictable.
>
> I dare say that if 800 numbers were routinely "SlashDotted",
> the outlook of voice network planners would be rather different,
> and that's ignoring the huge difference in bit-mass moved
> in the two cases.
>
> The deep intuition about network growth dynamics developed
> over the years with voice networks simply does not yeild
> workable results when applied to very large data networks
> which exhibit huge dynamic ranges of traffic slosh and the
> astounding doubling of offered load every year.  (and this
> is still the case even given how few people currently enjoy
> "broadband" access)
>
> So the statements about growth of offered load and growth of network
> capacity (no matter how much "ballyhooed") are not inconsistent.
> They are taking about two different but highly interrelated things.
>
>         cheers,
>         -mo
>
> ========================
> Michael D. O'Dell
> Senior Vice President, Chief Scientist
> UUNET - the Worldcom Internet Company
> Room E1-3-117
> 22001 Loudon County Parkway
> Ashburn, VA 20147
> Voice: +1-703-886-5890
> Fax:   +1-703-886-5806
> Email: mo () uu net



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