[e2e] QoS vs Bandwidth Overprovisioning

RJ Atkinson rja at inet.org
Tue Apr 24 17:11:08 PDT 2001

	It isn't clear to me that it is more expensive
to over-provision bandwidth in a backbone than to deploy
QoS in that backbone.  Some folks here seem to be asserting
that it is generally cheaper to deploy QoS.

	Many ISP folks believe that it is cheaper to over deploy
capacity, else there would not be so many ISPs that are
doing so.  Most (maybe all) of the Tier-1 ISPs [1] indicate
that they over-provision their network and generally engineer
it such that they don't lose packets inside their own backbone
(though some packets get lost at the handoff between backbones,
in my personal experience; pardon the purely anecdotal interjection).

	For many big providers, the recurring operations costs 
(e.g. NOC staff, deployment staff, troubleshooting staff, 
more generally: hiring and retaining clue) are believed to dwarf 
the capital costs of building a network -- iff one already has
dark fibre facilities in place.  This belief might relate to the
current lack of widely deployed QoS in large backbone networks.

	As to the costs of over-provisioning, once one has access
to dark fibre, it is not particularly more expensive (in capital
costs) to light it with Gigabit Ethernet than 10baseF or 100baseFX
(or sundry fibre-optic extenders).  Similarly it isn't really
that much more expensive to light up a segment with OC-48 than
OC-12 or OC-3.  My guess is that within 12 months time, lighting
at OC-192/10 GigE won't be hugely more expensive than OC-48 was
last year.  It seems more common that big providers have
access to dark fibre than the smaller providers, so this might
mean that smaller providers have more incentive to deploy QoS;
I'm not sure.

	As a sidebar, I note that the cost of dark fibre facilities 
trans-continent has dropped dramatically in North America in the 
past few years.  Similar cost drops appear to be starting in Europe 
as well.  Trans-Atlantic capacity has dropped substantially in cost;
trans-pacific capacity appears poised to have a similar cost

	So it just isn't clear to me that the marketplace is
going to drive the facilities-based providers to deploy end-to-end
QoS anytime particularly soon.  Maybe I'm totally wrong.
Kindly note well that this is a set of observations about
what appears to be happening, not a set of assertions about 
my personal druthers if I had a magic wand.

rja at inet.org

[1] A market definition of "Tier-1 ISP" might be the set of
folks, including UUnet, who don't pay money to UUnet to exchange
traffic.  A more technical definition (slightly different set
of providers, btw) might be based on having at least dual OC-48 
capacity cross-continent and a presence in all of the major 10-20 
metro areas.  For the purpose of this note, the precise definition
isn't so important as the general concept...

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