RE: [802.3ae_Serial] - link model modification requests
Tom,
Yes you are correct. I would like to offer a clarification on your first
statement. I believe you meant to say
> 1. "Additional loss" was only for -S, since it is the only variant that
> supports multiple fibers (not PMDs).
>
The LX4 PMD would also falls into this category, since it supports
multiple fiber types as well.
Paul
> ----------
> From: Lindsay, Tom[SMTP:tlindsay@xxxxxxxxxxxxxxxxxxxx]
> Sent: Tuesday, November 27, 2001 5:24 PM
> To: Kolesar, Paul F (Paul)** JV **; 802.3ae Serial
> Subject: RE: [802.3ae_Serial] - link model modification requests
>
> Paul -
>
> I apologize for not completely understanding your rationale. To attempt
> clarification, I would like to 1st step back a few revisions (I think it
> was in St. Louis) and recall how this began.
>
> 1. "Additional loss" was only for -S, since it is the only variant that
> supports multiple PMDs.
> 2. Unallocated margin was hidden and deemed "not available" for adding
> insertion loss or distance.
> 3. The values for Additional loss were derived by 1st determining which
> PMD had the least unallocated margin and then subtracting that value
> from the unallocated margins of the other PMDs. The PMD with the least
> unallocated margin was 2000 MHz-km, so it got 0 dB of Additional loss.
> 4. In other words, "reserved margin", as you name it, was really the
> unallocated margin for the PMD with the lowest value.
>
> Is my recollection correct? Is this still what we are trying to do?
>
> Tom
>
> -----Original Message-----
> From: Kolesar, Paul F (Paul)** JV ** [mailto:pkolesar@xxxxxxxxxx]
> Sent: Tuesday, November 27, 2001 10:25 AM
> To: '802.3ae Serial'; 'Dawe, Piers (Agilent)'
> Subject: RE: [802.3ae_Serial] - link model modification requests
>
>
>
> Piers,
> on the call today you mentioned that you were considering adding an
> input
> cell to the link model to account for splitter loss in EFM. You
> suggested
> that this cell could also serve the purpose of defining the additional
> loss
> allowed for 10G PMDs and thereby indirectly resolve my request for a new
> cell to allocate reserved margin.
>
> I've had a chance to think about the solution you suggested and believe
> it
> would be a sub-optimal compromise. While I agree that such a cell could
> serve both purposes, it has a drawback in the case of substituting for a
> reserved margin cell. The drawback stems from the fact that we have
> chosen
> to apply a fixed amount of reserved margin to each PMD type across all
> fiber
> types that support it. The resultant additional insertion loss
> allowance
> varies by fiber type. Thus, while a single value applies for reserved
> margin
> for each PMD across all fiber types, with the approach you suggested
> multiple values are needed for additional loss allocation, one for each
> fiber type. This could require a separate worksheet for each PMD/fiber
> combination, a complexity that I would rather avoid. It also means
> needing
> to tweak the additional loss entry to a value that results in the same
> margin at the specified link length for all fiber types supporting a
> particular PMD. I'd rather have the link model do the calculations. It's
> less obscure and less error prone.
>
> I think a cleaner approach would be to insert two new cells, one for
> each
> purpose. The additional loss cell would be used to allocate a fixed
> amount
> of loss (e.g. for splitters). The reserved margin cell would be used for
> making a portion of the power budget unavailable. The present "margin"
> column could be re-titled to "available margin", which under present
> philosophy would be used to fill in 10GbE table entries described as
> "additional insertion loss allowed".
>
> I hope this explanation makes my points sufficiently clear. If not, or
> if
> you have another view, please respond.
>
> Regards,
> Paul Kolesar
>