Subject: RE: QOS Routing - high level comments (long)

From: Paul Leach <[email-masked]>
Date: Mon, 8 Apr 1996 15:49:19 -0700

>----------
>From: 	[email-masked][SMTP:[email-masked]]
>Subject: 	Re: QOS Routing - high level comments (long)
>
>Hmm. Do you believe that with "enough" overprovisioning, and a traffic
>load
>which is reasonably consistent (i.e. modellable, I don't mean constant
>load)
>one can make a statistical guarantee of a specified level of service
>(of the
>kind I outlined in a previous message)? (Assume some non-cheatable
>priority
>marking scheme so that best-effort traffic spikes don't interfere with
>the
>delay of real-time traffic...)
>
Is there data on how much is "enough"?  It might make a lot of
difference whether it is 10%, 20%, 50%, 100% or 1000%.  It seems like
the intuition of the "reservationists" is that it is more toward the
1000% and the "anti-reservationists" is that its in the 10-20% range.
Which religion I subscribed to would be strongly influenced by the
answer, anyway.

>Paul

---

From: Curtis Villamizar <[email-masked]>
Date: Tue, 09 Apr 1996 15:25:50 -0400

In message <c=US%a=_%p=msft%l=[email-masked]
> Which religion I subscribed to would be strongly influenced by the

In 1993 to 1994 the NSFNET backbone was almost completely
unconmgested.  It had very close to zero loss.  What was congested was
the regional networks or access circuits.  There were a number of well
connected sites (NSF funded supercomputer centers and some others)
that had a clear shot to the NSFNET backbone (uncongested DS3).  The
supercomputer centers had uncongested paths between each other.
Connectivity to Europe was congested (not as bad as now) and smaller
providers were congested, but mostly fairly mildly congested.

In the US, backbone capacities had barely increased since 1993.  The
difference is their are now more commercial providers with DS3
backbones.  Adding more backbones rather than making a single faster
backbone absorbed growth for a while.  Adding redundancy rather than
faster circuits has been the preferred approach.  The problem is the
major providers are all getting congested despite this.  Over the past
two years demand has grown significantly faster than capacity.

During the NSFNET days the measure of congestion was that a link 70%
utilized over any 15 minute period was relatively rare.  This means a
supercomputer center could let go 3-5 minutes of traffic that fills
whatever capacity is left and still call the link uncongested if on
average it was running under 70%.  It turns out the NSFNET never came
anywhere near this level of congestion.  The point of setting this
goal was that traffic dominated by a few TCP flows (the high bandwidth
users) needs very little loss to keep within link capacity.  The
NSFNET was more PPS limited than anything, but the supercomputer
applications used big packets and so this traffic could be added
without stepping on that bug.  In the latter days we were playing with
buffering and experimenting with RED to further improve this, though
we never got RED deployed.

Various major US providers are now planning or executing capacity
upgrades that may (at least temporarily) bring their backbones to this
same state.

Another source of congestion has been the provider interconnects.
Many of these have upgraded from single FDDI rings to bridged FDDI
rings and are moving customers (providers) of shared FDDI rings onto
private rings.  The interconnects that have chosen ATM are upgrading
to more advanced switches.  Some of the larger providers are
establishing private peerings at additional cities to reduce load on
the interconnects and to reduce load on their own backbones by not
hailing large amounts of traffic away from an area on one provider
network and back to the same area on another provider network.

So to answer your question, in the US probably closer to the 10-20%
range for most backbone providers.  Some may be in the 50-100% but are
reagarded as poor IP providers and some of the smallest providers may
be in the 1000% range.  In the UK they have lots of excess capacity.
Most of Europe has historically been more congested than the US due to
articficially high circuit prices.  The cross Atlantic links are too
small and are among the most congested.

None of this is at all secret and is discussed quite openly in places
like NANOG meetings.

Curtis

ps- I think this digression is going far enough off tangent.  It is
not certain whether major IP providers will be able to get ahead of
demand again and stay ahead.  I think the major ones all intend to try
to get and stay ahead of demand.  Part of the problem is finding
routers that are really up for the job.