Ryan,
what is the typical and maximum power
dissipation of the SFP+ module with the integrated CDRs that you show below?
Regards,
Paul Kolesar
Ryan Latchman <Ryan.Latchman@xxxxxxxxxx>
08/30/2008 09:04 AM
Please respond to
Ryan Latchman <Ryan.Latchman@xxxxxxxxxx>
To
STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
cc
Subject
Re: [802.3BA] 802.3ba XR ad hoc next
step concern
Ali,
As previously discussed, your
comparison with XFP is flawed. The cost and power estimates given
for XR assumes CDR integration which is very feasible. For your reference,
below is an example PCB of an SFP+ module with CDRs in both directions
(CDR with integrated laser driver in the Tx direction, CDR with integrated
limiting amplifier in Rx direction). The benefits of this are clear.
Systems designers don’t need to worry about jitter budgets (a topic
which has plagued SFP+), and it saves them from having to put standalone
signal conditioners on the line card, saving material amounts of cost and
total system power.
The CDR based solution for
achieving extended reach is the most trivial solution since:
1)
It
uses a simple host interface (XLAUI / CAUI) which can be leveraged to achieve
all types of 40GbE or 100GbE PMD interconnect
2)
XLAUI
/ CAUI enables lots of design flexibility. Hosts don’t care that
the MMF channel is longer.
3)
It
is well proven technically.
Sorry I missed the XR call,
but I was on a plane at that time. I look forward to additional discussion
on this topic.
Best Regards,
Ryan
From: Ali Ghiasi [mailto:aghiasi@xxxxxxxxxxxx]
Sent: August 29, 2008 3:48 PM
To: Ryan Latchman
Cc: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx; DAWE,PIERS; Booth, Bradley
Subject: Re: [802.3BA] 802.3ba XR ad hoc next step concern
Ryan
If you compare the cost difference between XFP and SFP module you will
find more than 50% cost difference.
Adding a CDR to an SMF module will add about 5% to the BOM and about 15%
to an MMF module BOM.
As you know the final cost of the module will increase by greater amount
than the BOM cost increase.
You assumption about integrating CDR in the LA/LD may require to use special
process, may limit availability, may have
technical issue of integrating TIA in to a CDR, or may have physical constrain.
During the XR call yesterday we had discussion how the system cost increase
if the port density is reduced my be the greatest cost
factor.
Thanks,
Ali
Ryan Latchman wrote:
Hi Piers,
When considering the 5% cost
adder to the module, take a look at the delta area of adding CDR functionality
to a limiting amplifier or laser driver. I think you will find the
extra area is small, particularly when you take into account bond pads
of the LA/LD. Now take into account the other components which contribute
to the cost of the module (ROSA, TOSA, uC…). I think you will find
that a 5% adder is very realistic.
The 5% sounds unlikely (I would
have expected more) and similarly the 17% (what I've seen of the surveys
says that when invited to lay out equipment anywhere with a 300 m constraint,
very few links even go beyond 100 m).
But I'm actually writing to reply
to your paragraph about compliance points. Remember that for Gigabit
Ethernet, in 38.5, Table 38-10, the Total Jitter at TP1, TP2, TP3 and TP4
are all normative.
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]
Sent: Wednesday, August 27, 2008 8:18 PM
To:STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3BA] 802.3ba XR ad hoc next step concern
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.
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.
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
1480 Arthur Ave.
Louisville
CO 80027
Tel 303 530 3189 x7533.
mike.dudek@xxxxxxxx
From: Dove, Daniel
Sent: Wednesday, August 27, 2008 2:00 PM
To:STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3BA] 802.3ba XR ad hoc next step concern
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.
