RE: Signal vs. Idle debate (A picture is worth a thousand words)
It seems like people are getting pretty excited about this...
I agree with Dan's argument that mid-span insertion via the unused pairs
will be easier; however, the committee would be doing themselves, the IEEE,
and the customer base a large disservice if we don't make a strong attempt
at powering via the signalling pairs as well.
JR
At 04:21 PM 5/5/00 -0700, Ralph.Andersson@xxxxxxxxxxx wrote:
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>Dan's picture sums it all up. Let's be clear about what the objectives
are for
>this standard. Mid-span isertion is not an option... It is a requirement. As
>per the March Plenary minutes :
>http://grouper.ieee.org/groups/802/3/af/public/mar00/minutes_0300.pdf
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>Motion
>Move to add a requirement that:
>The solution for DTE powering shall support mid-span insertion of the power
>source.
>Moved: A. Anderson Second: D. Dove
>Technical 75%
>Y: 33 N: 0 A: 1 Time: 2:45PM
>Motion passes.
>
>The benefits of this requirement is obvious:
>1. It allows a low-cost retrofit to existing hardware in the wiring closet.
>2. It does not require the replacement of existing switch hardware.
>
>The concept of adding mid-span isertion via the un-used pair is
>straight-forward
>and does not include any hardware that is not readily available, no
>non-standard
>transformer is required and, as Dan points out, it does not affect return
loss.
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>Phantom power via the signal pair requires the addition of an additional
>transformer in the signal path; the effect on the return loss is unknown
and is
>may be detrimental. Geoff Thompson stated recently:
>"There is currently very little margin in a Class D link for new elements.
>Every new element that is introduced into a link has losses and mismatches.
>In the cabling community the competition for the exisiting margins is
>already oversubscribed by legitimate factions with very real needs."
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>In the last couple of days there have been alot of voices justifying using the
>signal pairs because it allows inclusion of 1000BASE-T. It seems to me that
>using the unused pairs, rather than the signal pair, will allow the return
loss
>specs of the 100BASE-TX standard to be met with no additional high quality
>transformer elements. If we as a task force can show that a transformer
exists
>that will allow the return loss specs to be met, as the Phantom group
>assures us
>it can, then this solution solves the Gigabit need as well. Two birds, one
>stone, with the risk assigned where it belongs. We need to remeber that
>Gigabit
>inclusion is not required of this task force.
>
>...Ralph
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