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Brian, it is a good question, but this
reflector is for development of the standard rather than advice to implementors. Ayal, the IEEE 802.3ap website has a
public area with all the presentations that have been made to the task force. You
might take a look at that for the investigations into the backplane materials
that were made to determine the channel model. Regards, Pat From: Brian Seemann
[mailto:brian.seemann@XILINX.COM] Hi Ayal, You have asked a very simple, reasonable
question. The amount of time and energy that the 802.3ap contributors
spent on this is staggering. But over the past several years, we have
learned a great deal about the role of materials and connectors in high speed
signal integrity. A large amount of this work has been contributed in
IEEE 802.3ap. Here are some points that address some
aspects of your question: ·
In general, the industry has moved forward
significantly in what can be done with mainstream materials, connectors and
manufacturing processes. ·
The IEEE 802.3ap standard specifies the
performance of the transmitter and the receiver. This is what will
ultimately determine the channels servable by the standard. ·
The channel model (Section 69.3) is informative
only, to give guidance to backplane builders for what will likely work and not
work with the transceivers. ·
The standard will not specify or even recommend
particular connectors, materials or construction methods. ·
Careful layout design techniques are probably the
most performance-effective and the most cost-effective measures to ensure
signal integrity. ·
There are 10Gbps-capable connectors available
from several manufacturers. ·
The performance of good connectors can be
completely obscured by poor layout design methods. ·
There are multiple contributions showing
successful 10Gbps performance on materials such as Nelco 4000-13, Nelco
4000-13SI, and Isola FR408. Again the standard will not make any
recommendations about materials. ·
In many cases on the line cards, lower grade
(higher loss) board material (such as 4000-6) has actually been shown to be
preferable to higher grade (lower loss) material. This is because higher
loss can reduce the Q (reflection effect) of stubs. ·
The performance of good material can be
completely obscured by poor layout design methods. ·
Vias from top layer traces are probably the most
disruptive layout feature to signal integrity. ·
Backdrilling vias to eliminate the stub is viewed
by many manufacturers as cost feasible. Others
on this reflector can weigh-in with more insightful or alternative
perspectives. From: Ayal Lior [mailto:Ayal.Lior@tera-chip.com]
Hi, I am new to this reflector and have a very basic question. We would like to know what is the recommended material and
connectors for backplane to drive the 10GBase-KR. Target application is chassis with maximum length of
40" with two connectors. Any feedback is appreciated. Thanks, Ayal Lior |