Re: worth reading -- QOS Author is Motorola, Chief Software Architect

[David Farber <dave () farber net>]

________________________________________
From: Richard Bennett [richard () bennett com]
Sent: Tuesday, June 24, 2008 4:58 PM
To: David Farber
Cc: ip
Subject: Re: [IP] Re:   worth reading --  QOS  Author is Motorola, Chief Software Architect

One of the great myths of network history is the notion that Bob Metcalfe's Ethernet "beat" Token Ring and other 
QoS-enabling systems. In fact, the networks that we call "Ethernet" today are hybrids that incorporate some of the 
mechanisms pioneered by coaxial cable Ethernet alongside some that were borrowed from Token Ring. The cable topology 
and technology in modern Ethernet are closer to Token Ring than to coaxial cable with distributed transceivers, stars 
with twisted-pair cabling. And similarly, we now have switches in the first hop, which can and do enforce QoS through 
priority bits in the VLAN tag and by configuration in the switch., much as Token Ring did with its priority classes. 
And we have similar mechanisms for simple QoS by priority in WLAN systems, following 802.11e and WMM.

So the history of layer two networking actually illustrates the broad utility of QoS at the same time that it 
illustrates the value of KISS: simple QoS-by-priority has beaten complex QoS-by-reservation pretty handily.

We need QoS on data links where the level of traffic fluctuates wildly moment-by-moment, and these are most often 
first/last hop segments. As we approach the Internet core, statistics maintain more constant levels of traffic as 
user-based traffic fluctuations tend to average out.

We currently protect the core from overload by constraining the amount of data that can enter the network from the 
leaves, but as we upgrade the first hop to accommodate peer-to-peer, we may very well shift overload further into the 
network.

So let's bear in mind the correct definition of KISS as a design principle: make your systems as simple as possible, 
but no simpler.

RB

David Farber wrote:

________________________________________
From: Tony Lauck [tlauck () madriver com<mailto:tlauck () madriver com>]
Sent: Tuesday, June 24, 2008 2:19 PM
To: David Farber
Subject: Re: [IP] worth reading --  QOS  Author is Motorola, Chief Software Architect

If we take out of the argument questions (or fears) of price
discrimination or other monopolistic practices, it becomes a question of
engineering. Is it better to provide adequate service by special
handling of certain "demanding" types of packets or is it better to
provide adequate service by resource sizing with simple but fair
scheduling policies?  There is a trade off between devoting resources to
developing and implementing QoS mechanisms throughout the network and
host computer stacks vs. devoting resources to provisioning additional
capacity.

There is approximately one half century's worth of history. This is a
debate that started with Bell Lab's circuits vs. MIT's packets. This is
token ring vs. Ethernet and later FDDI vs. Fast Ethernet. This is ATM
vs. IP. The argument has been nearly continuous throughout the history
of computer networking.

Historically, the approaches that succeeded in the marketplace have been
the simple ones that could more easily ride the technology curve driven
by Moore's law. There are always people trying to make a career or
business out of new complexities, and occasionally some of them succeed.
  Perhaps now is the time for more complex systems, but I doubt it. I
have seen simple approaches win out too many times. There has always
been a reason why the complex approaches lost, and these reasons have
many: cost, performance, reliability, time to market, compatibility,
ease of use, etc. Others, who fancy themselves masters of complexity may
have a different opinion.

Dave Crocker has made one specific claim regarding transient contention
being the difference between "almost never" and "never". This is not an
meaningful distinction in the real world, because real systems fail. One
is always working with probabilities. QoS services with real-time
guarantees require redundancy coupled with real-time fail over, and this
has historically been achieved only with high levels of redundancy. High
degrees of "almost never" can be achieved at high cost. "Never" comes at
infinite cost.

[Along this line, my advocating of KISS is not intended as an argument
for government mandated network neutrality. There is nothing less simple
in today's world than Government.]

Tony Lauck
www.aglauck.com<http://www.aglauck.com>



David Farber wrote:


________________________________________
From: Dave Crocker [dhc2 () dcrocker net<mailto:dhc2 () dcrocker net>]
Sent: Tuesday, June 24, 2008 11:07 AM
To: David Farber
Cc: ip; Waclawsky John-A52165
Subject: Re: [IP] QOS  Author is Motorola, Chief Software Architect

David Farber wrote:


From: Waclawsky John-A52165 [jgw () motorola com<mailto:jgw () motorola com>] Sent: Monday, June 23, 2008
1:08 AM To: David Farber Subject: RE: [IP] Re:   Net Neutrality: A Radical
Form of Non-Discrimination by Hal Singer

Hi Dave, Some QoS perspectives that I have learned: First, the main problem.
QoS really isn't needed when you have big pipes.



This view has gained popularity in recent years and it seems to be based on two
misunderstandings.  The first is that end-to-end performance is dictated by the
size of pipes and the second is that pipes are always large or that we can
guarantee that eventually they all will be large.

Packet switching is more about the switching than the pipes.  The path from a
one random end-system to another has quite a few switching points. This thing
called queuing comes into play when there is transient contention for resources.
This includes contention for use of each pipe along the way, but also contention
in switches and, by the way, contention in either of the end-systems.  (I'm
qualifying with "transient" because sustained contention means that the system
is fundamentally overloaded; queuing can't help there.)

The premise behind the "big pipes" view is that we don't have transient
contention. It's simply not true.

What is true is that there are common scenarios where transient contention is
almost never a problem.  But the difference between "almost never" and "never"
counts for everything in a world seeking reliability.  Especially if you want to
cover a full range of scenarios.

One set of scenarios left out by "big pipe" devotees is a vast portion of the
world with limited resources.  While this obviously includes many remote or
developing environments, it also includes less-capable channels such as mobile
devices.

It should also be noted that there is a tendency for the core of the Internet to
have less contention than access networks at the edge.  We can wave our hands
and say that the edges will eventually catch up, but history suggests otherwise.

A persistent lesson over the history of packet switching is that there is a wide
range of resource capabilities and anything designed to rely on high-end
capabilities disenfranchises participants and systems that are not so privileged.

"QOS" has indeed had a problematic history over the life of packet-switching,
but this seems to be because it is difficult to design in a way that is useful
-- and then deploy it throughout the infrastructure -- rather than because it
isn't needed.

Basic Internet capabilities were designed to maximize use of the channels, but
at the cost of inter-packet arrival variance.  Any application needing to
sustain a specific transmission rate with specific (and low) variance is at
risk, without some underlying design to ensure the necessary performance.

Anyone with experience to the contrary might want to review their sampling
methodology against the full and realistic set of Internet scenarios.


d/
--

   Dave Crocker
   Brandenburg InternetWorking
   bbiw.net



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--
Richard Bennett




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