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Mike, It isn't just
the cost. The power is also important for those ports. Pat
Folks,
I agree that the
discussion of the possibility of lowering latency does not imply impact on the
original BMP brought forth by the study group. That is to say
we’ve no less market potential than was presented in the 5 criteria if we do
nothing to lower latency. On the
other hand the potential could be greater if the
latency can be lowered. Joel
brought up a good point that when end users go looking for equipment, latency is often used by vendors as a lever to edge out
their competition. In the
clustering domain, Ethernet is not the only choice. Geoff pointed out that Ethernet was designed for loosely coupled systems. Alternative technologies for
clustering are more tightly coupled and have
significantly less latency than Ethernet. Furthermore, Network Interface Cards
(NIC) for these systems are very inexpensive compared to 10 Gigabit Ethernet
NICs.
The folks I know who build clusters are willing to pay for the switch
ports but they expect the NIC to be close to very low cost, meaning it doesn’t
cost much more to get a motherboard with the NIC built-in than without it
(similar to 1 GbE now). So this leads to a few
questions: is the potential market that could be gained by lowering the
latency so significant that it’s worth doing? Does anyone have market data on this?
Even if the market data suggests
it would be a good thing to do, would that justify the trade-offs to make it
happen? Should we just wait until after the
Data Canter Ethernet CFI before we even discuss it further in 10GBASE-T?
Mike
-----Original
Message-----
From:
owner-stds-802-3-10gbt@majordomo.ieee.org
[mailto:owner-stds-802-3-10gbt@majordomo.ieee.org] On Behalf Of Jonathan
Thatcher
Sent: Monday,
February 23, 2004 1:06 PM
To:
'Geoff Thompson'
Cc:
'stds-802-3-10gbt'
Subject:
RE: [10GBASE-T] latency
Me-thinks you are
being a little harsh here. I do not believe there is any implication that BMP
is not met unless low latency applications are supported. The implication is
simply that the BMP is B'er if latency is
less.
Now, if the cost (C)
of achieving B'er BMC is out of balance, then it certainly should not be
pursued. But if additional C has the potential to B'en BMC then it
is worthy of discussion.
If you wish to take
the position that no B'er BMC is worth additional C, that is
fine.
I, for one, would
like to hear other opinions. And, without trying to be harsh myself, I think
you should also.
p.s. your point about
10GBASE-CX4 is valid, within its distance limits. Of course, one of the major
latency aspects of low latency is distance divided by the speed of light.
While 10's of km for low latency is absurd, 10's of meters may not be.
-----Original
Message-----
From:
owner-stds-802-3-10gbt@majordomo.ieee.org
[mailto:owner-stds-802-3-10gbt@majordomo.ieee.org]On Behalf Of Geoff Thompson
Sent: Monday, February 23, 2004 12:33
PM
To: Bruce
Tolley
Cc:
jonathan.thatcher@ieee.org; 'stds-802-3-10gbt'
Subject: RE: [10GBASE-T]
latency
All-
I am having a little trouble with some
of the assumptions of this entire thread.
If you have a special need
for low latency at 10 Gig for cluster computing then we already have a
solution, 10GBASE-CX4.
I would say that it is not particularly
appropriate at this time to even presume that we have legitimate
requirements for Ethernet where the coding delay in a PHY is significant for
a speed for which we are not doing CSMA/CD (whose round-trip time was the
traditional driver of the low latency requirements).
There has been a
lot of talk about fiddling the latency to meet the requirements for a topic
for which there has not even been a Call For Interest!
This leads me
to believe that all of the talk in getting this study group approved, in
which there were claims of more than adequate "Broad Market Potential" were
not quite as true as was depicted. There was no mention of the BMP of
10GBASE-T being latency dependent during the PAR proposals.
Does all
this discussion mean that you wish to revisit the basis on which the
10GBASE-T was granted?
Ethernet is at its MOST BASIC level is
designed to be a connection for loosely coupled systems. This has been the
source of its success. I am perfectly willing to explore new avenues for
Ethernet. I am not willing to cross out multiple pieces of its basic nature
just to chase every corner of the data transfer market. It is NOT just the
name "Ethernet" that is the basis of its success.
The most
significant things that 10GBASE-T needs for its success
is:
Silicon
processing that can tolerate its speed and complexity
requirements
A
large enough market for a general purpose "Ethernet" interconnect at 10G
to
pay
for the development and
drive
the part cost down
Geoff
At 11:16 AM 2/23/2004 -0800, Bruce
Tolley wrote:
Jonathan
Thanks for the summary
I
would argue that early 10GBASE_T switching products should be sold to early
adopters at National Labs and other R&D sites building clusters. We need
this community to come to the TF and state its latency requirement in the
2006 timeframe and determine the tradeoffs.
Bruce
At 10:54
AM 2/23/2004 -0800, Jonathan Thatcher wrote:
There have been
numerous interesting and correct comments made. A subset of these apply only
in certain contexts. To that end, I will attempt to add some
context.
There is little
question that lower latency increases the market potential. There is little
question that lower prices (read that less complexity), and earlier time to
market also increases the potential market. The problem is that these fight
against each other, and the optimization point is not
clear.
I presume that
there are two principal application spaces for 10GBASE-T in the near term:
data center and enterprise (home and school will probably have to wait a
couple of years :-). If you want a strict boundary between these two spaces,
I can't provide it. So we will have to deal with some ambiguity. In the
enterprise, it is difficult to argue that low latency is as critical as low
price. The exception to this would be low latency applications that want to
be set up as a "grid computer," which I will lump into the "data center"
bucket.
The data center, on
the other hand, has instances where both low latency is required (clustered
computing) and higher latency is acceptable (most file serving). From a
parallel computing perspective, there are classes of problems (applications)
that range from low latency NUMA to those that are "embarrassingly parallel
(e.g. http://setiathome.ssl.berkeley.edu/)."
From the
perspective of the upcoming "Data Center Ethernet" (may not be the best
name) call for interest, the intent is to explore those means that can be
used to decrease latency in Ethernet networks. If one is to presume that
this should be a key application space for 10GBASE-T, then it would be
interesting to understand the trade-off between latency and complexity. It
may be the case, that even under the most complex scenario, that 10GBASE-T
latency is simply insufficient for entire classes of low latency
applications.
So, the question
remains, what does the complexity vs latency curve look like? I expect that
it is something like the left side of a bathtub curve (vertical axis is
latency, horizontal axis is complexity). What is the inflection point? What
is the slope of the falling portion of the curve? What is the
asymptote?
jonathan
Bruce Tolley
Senior Manager, Emerging
Technologies
Gigabit Systems Business Unit
Cisco Systems
170 West
Tasman Drive
MS SJ B2
San Jose, CA 95134-1706
internet:
btolley@cisco.com
ip phone: 408-526-4534
"Don't put your hiking
boots in the oven unless you plan on eating them."
Colin Fletcher,
The Complete
Walker
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