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Hi John, I agree with your conclusion. The flexibility
available with either a PPI or a XLAUI / CAUI interface enables a variety of
implementations which can include the XR reach objectives. I think an
annex which outlines how to achieve longer reach using the tools available in
the standard will provide significant implementation flexibility. Best Regards, Ryan From:
John DAmbrosia [mailto:jdambrosia@xxxxxxxxxxxxxxx] Brad, Thank you for bringing up these points. During
the course of this project, I have emphasized that we are developing an
architecture that should enable as many implementations as possible, and not
writing an implementation specification. You have hit the nail on the
head with your points. The base proposal for the BASE-SR physical layer
specifications is based on the jitter associated with a non-retimed interface
to achieve 100m. There has been general discussion that adding retimers
to a BASE-SR module would then extend reach. Per http://www.ieee802.org/3/ba/public/AdHoc/MMF-Reach/Comparisons_xr_01_0722.xls,
and column D (latchman_xr_01_0508), CDR’s on one side would extend the
reach to 168m and CDRs on both sides would be 208m (both #’s are based on
OM3 fiber). So if we review the adopted architecture proposal,
and consider implementations for different reaches, what do we find? The thing is that we approved an architecture with
the XLAUI / CAUI optional interface. This is a retimed interface.
So it seems to me that we have developed an architecture where either
implementation using the same PMD sublayer could be developed, i.e. a PPI
(non-retimed interface) to a module or a XLAUI / CAUI (retimed interface) to a
module. Thinking about how to implement in the spec - The
minimum guaranteed interoperability would be 100m, which is in the current
specification. An informative annex could then go into engineered links
for 150 and 200m, based on the use of modules with either the PPI or the XLAUI
/ CAUI interfaces. Pardon the choice of words, but I think this would be
rather informative anyway, as the spec already enables both types of
implementations. Based on this, it would seem that the TF has been
successful in developing an architecture where implementations could be
developed to support either reach. Regards, John From:
Brad Booth [mailto:bbooth@xxxxxxxx] Dave, I agree. A 5% cost
adder seems reasonable for a 17% increase in broad market potential. I do wonder if part of
the problem is the compliance points TP0, TP1, TP1a, TP4, TP4a and
TP5. In past efforts such as 802.3z and 802.3ae, these compliance points
have been left up to MSAs and only TP2 and TP3 were of concern. Now the
task force is dealing with such issues as modules and the cost impact of
various implementations. IMHO, IEEE 802.3 was trying to avoid
writing implementation specifications and was focused on compliance
specifications. Could it be that these compliance points are causing the
task force some heartache because it results in an implementation
specification? Just food for thought... Thanks, Brad From:
Chalupsky, David [mailto:david.chalupsky@xxxxxxxxx] The 20% cost premium
applies to only one of our proposed XR alternatives. According to the
alternatives spreadsheet (Comparisons_xr_01_0708.xls) the CDR option adds only
5% module cost premium over the base proposal and provides reach of 168m to
251m (across the OM3/4, one-sided/two-sided matrix). I’m struggling to
keep up with the conversation here – but I believe that the 5%
alternative addresses the same problem as the 20% alternative, right? On that assumption I will
rephrase Dan’s non-rhetorical question to address a 5% cost adder for 17%
increase in coverage: If I have the choice
between: A) carry two product
SKUs: 100m and 150m, with 5% Bill of Material cost delta on the 150m product;
or B) carry only the 150m
product I would accept option B
& use only the 150m module even though I know that most of my customers
will use it at <100m. By considering only the
bill of material of the module we are missing two aspects of the big picture on
cost. 1) Carrying multiple product SKUs through design, validation,
manufacture, customer qualification, customer confusion, etc. adds cost. Regardless of whether 802.3ba adds a second objective, if the
module supplier base develops two different module solutions for 100 &
150m, then the 100m solution will carry an intangible cost burden and the
desired 0% cost adder for 100m will not be achieved anyway. 2) The module is not the whole solution. The CDR module
solution does not add cost to the host. Thus a 5% increase in module cost
is less than 5% increase in the total cost of the switch plus modules. I appreciate that the
task force is learning from the history of 10GBASE-SR: that over-specifying the
solution had a long term cost impact. However, we should take
away another lesson from 10Gbit: that providing too many options confuses
the customers & slows adoption. I strongly urge the task
force to provide a single solution for parallel MMF. I believe that
it’s worth a 5% cost adder to the module to achieve that. I really have no personal
(or commercial) reason to prefer the CDR option. I’m just looking
at the 5% figure in the spreadsheet & wondering why this isn’t a
no-brainer. Thanks for your time, Dave Chalupsky From:
Hi Mike,
Assuming we make the
decision that we want to stick with the "standard" model at 100m to
keep those customers we would lose by adding cost, does the IEEE standardize a
150m solution or do we let the market solve that problem on its own? This is not a rhetorical
question, although it might appear to be. Can someone provide any
insight on the sensitivity of the market to an additional cost of 20% for every
100m link to satisfy the additional reach? If the market is
insensitive to cost (on this scale) then perhaps the additional reach is
justified. If the market is going to be sensitive to that differential cost,
then the question falls back to whether the IEEE wants to do a 150m spec or
leave it to a market-defned solution. Dan From:
Mike Dudek [mailto:Mike.Dudek@xxxxxxxx] Hi Dan Of course if we
don’t increase the cost of the basic Grade A model and have a Grade B
version of the same part for extra reach with the Grade B version being loaded
with any additional costs of handling two product codes and any additional
testing, then we shouldn’t lose any customers. Regards Mike Dudek PMTS Standards & Technology JDS Uniphase CO 80027 Tel 303 530 3189 x7533. mike.dudek@xxxxxxxx From:
Let me re-state
one word of that message. From:
Hi Steve, Yes that helped a lot. I
hope the others on the list are not irritated by my request for repetition of
the data. Given the data, it truly
is a challenging issue. I see a 20% premium for a 17% increase in coverage. This means the confidence
in the numbers is exceptionally important and assuming they are accurate, a
judgement call by the committee on whether or not a 17% increase in port
coverage justifies the 20% increase in cost. This is important because
if you increase the *COST* of a solution by 20%, you
may decrease the number of customers who are willing to buy it by more than
20%. Thus, in the overall mix, it might turn out to satisfy less customers
overall. Its a pretty challenging
judgement call IMHO. Thanks for providing the
data. Dan |