RE: [802.3ae_Serial] - link model modification requests
All -
I want to close on this portion of Paul's initial email. My motivation
for doing so is not technical, but purely for documentation.
If I apply the equations implied below to the spreadsheet as it
currently exists (10GEPBud3_1_16a.xls), I do NOT get anything close to
what is in the document (D3.4).
Looking further, I discovered that cell L7 includes 1.5 dB connector
losses plus another number. I do not know where these other numbers came
from, but they appear to be inputting the anticipated values for
additional_insertion_loss_allowed. This is in conflict with the
equations implied below, which say that
additional_insertion_loss_allowed should be an output or result.
If I remove the extra number in cell L7 and then apply the equations
below, then everything works exactly per D3.4 (within 0.1 dB anyway,
possibly due to roundoff). I would like this approach to be implemented
in the spreadsheet.
Also, the table row named Allocation_for_penalties is not simply
penalties, but adds unallocated_margin after additional
_insertion_loss_allowed is subtracted. For documentation, it would sure
be more clear if that row is renamed to
Allocation_for_penalties_and_other margin. I understand the desire to
not give the impression that more margin is available, but I also do not
want anyone to think they can develop/incur penalties beyond the values
in column V.
Note1: other than renaming the row, these comments do not affect the
standard, only the spreadsheet as documentation and general purpose
tool. I do NOT plan to submit comments on this topic this time around,
but do plan to during sponsor ballot.
Note2: I have only checked Table 52-10 (-S). I have not checked any of
this for -LX4 and -E variants.
Comments?
Tom
425/672-8035 x105
-----Original Message-----
From: Lindsay, Tom
Sent: Tuesday, November 27, 2001 4:43 PM
To: 'Kolesar, Paul F (Paul)** JV **'; 802.3ae Serial
Subject: RE: [802.3ae_Serial] - link model modification requests
Paul - sorry about being myopic on clause 52 and the loose usage of
"PMD".
If what we say below is true, then the reserved margin value is
pre-determined and would be an input to a new cell that would result in
allowable additional loss as an output. The cell would appear in each
sheet of multiple-fiber group supported by a common PMD (did I say that
right?). The cell equations would be of the form:
fibertype_unallocated_margin - reserved_margin
where
reserved_margin = min(all_unallocated_margins_for_that_PMD)
I agree this would be better isolated from an input cell that reserves
additional loss for splitters, etc.
So do I understand what you are after?
Tom
425/672-8035 x105
-----Original Message-----
From: Kolesar, Paul F (Paul)** JV ** [mailto:pkolesar@xxxxxxxxxx]
Sent: Tuesday, November 27, 2001 2:43 PM
To: 802.3ae Serial; Lindsay, Tom
Subject: 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
>