The Qos PipeDream [Was: RE: Two Tiered Internet]

Fri Dec 16 20:03:26 UTC 2005

Thus spake "Christopher L. Morrow" <christopher.morrow at mci.com>
> On Fri, 16 Dec 2005, Min Qiu wrote:
>> Not 100% true.  Through I agree QoS has little impact in the core
>> that has OCxx non-congested backbone (more comments below).  In the
>> edge, it does has its place, as Stephen Sprunk and Mikael Abrahamsson
>> explained/described.  I recalled we were busy at one time to find out
>> why one of our _most_ important T1 customer's poor VoIP performance.
>> It turned out his T1 was peaked in those peroid.
>
> yup, for t1 customers (or dsl or dial) qos matters only if your like is
> full when you want to do something with stringent delay/jitter/loss
> requirements (voip).  Possibly a better solution for both parties in the
> above case would have been MLFR ... possibly. (someone would have
> to run the numbers, I'm not sure how much the 'qos' service costs in
> real $$ not sales marked-down-for-fire-sale $$)

MLFR (you mean FRF.8?) works, but you first need to learn how to do FRTS, 
which is a nightmare in itself.  MLPPP LFI is trivial to set up.

However, MLFR/MLPPP only help when paired with an intelligent queueing 
algorithm; with FIFO and even WFQ they're useless.  You've gotta go to 
CBWFQ/LLQ to get the benefits.

>> it only move the threahold in the core from DC3 to OC12 or OC48 (see
>> Ferit and Erik's paper "Network Characterization Using Constraint-
>> Based Definitions of Capacity, Utilization, and Efficiency"
>>  (http://www.comsoc.org/ci1/Public/2005/sep/current.html I don't have
>> the access).  I'm not sure the study can applied to customer access
>> edge where traffic tend to be burst and the link capacity is smaller in
>> general.
>
> Maybe part of the discussion problem here is the overbroad use of 'QOS in
> the network!' ? Perhaps saying, which I think people have, that QOS
> applied to select speed edge interfaces is perhaps reasonable, I'd bet it
> still depends on the cost to the operator and increased cost to the
> end-user. it may be cheaper to get a second T1 than it is to do QOS, and
> more effective.

For some scenarios, yes, but in most environments the peaks would still fill 
the pipes, just for half the time.  And, as we all know, the faster the 
network gets, the more creative ways people find to fill those pipes.  It's 
a rat race, but your telco salescritter will love you for it.

Overprovisioning the last mile is, at least for now, far more expensive than 
training a monkey to apply a cookie-cutter MLPPP/LLQ config; from the 
comments here, consensus is the opposite is true in the core.  My experience 
is with large-but-slow networks (thousands of sub-T1 sites) so I can't say 
how true that is, but it sounds right.

> Alternately, customers could use other methods aside from QOS to do the
> shaping, assuming 'QOS' is defined as tos bit setting and DSCP-like
> functions, not rate-shaping on protocol or port or source/dest pairs.

QoS has lots of different meanings, thanks to the marketeers.  The one most 
customers think of, and the only one that's provably wrong, is "QoS is a 
magic wand that gives you free bandwidth."

S

Stephen Sprunk         "God does not play dice."  --Albert Einstein
CCIE #3723         "God is an inveterate gambler, and He throws the
K5SSS        dice at every possible opportunity." --Stephen Hawking 