Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: [BP] Recommended material and connectors



Pat-

I think you are being a little harsh.
Folks coming from the rest of the 802.3 standard (like Ayal) have a little higher expectation for a constrained implementation of the transmission channel (lie, e.g. a cabling standard) that is the case here.

Ayal's question is perfectly reasonable in the context of all of our other PHYs.

It is just that the real world answer isn't as good.
Given that, I thought Brian did a great job on dancing on the edge

Geoff



At 12:01 PM 8/22/2005 , Pat Thaler wrote:

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.

www.ieee802.org/3/ap

Regards,

Pat

 

From: Brian Seemann [mailto:brian.seemann@XILINX.COM]
Sent: Monday, 22 August, 2005 11:34 AM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: Re: [BP] Recommended material and connectors

 

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.

 

Brian Seemann

 

 

From: Ayal Lior [mailto:Ayal.Lior@tera-chip.com]
Sent: Monday, August 22, 2005 8:54 AM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: [BP] Recommended material and connectors

 

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