RE: [10GBASE-T] latency
Geoff,
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.
jonathan
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