Re: [802.3BA] Discussion on 40G for => 10 km SMF
Jeff
I do not know your background.
However I found, in your comment below, you misunderstood the optical
transmission technologies.
I do not want to argue line by line.
Just I would like to point one sentence:
"The biggest downside of 40G serial, seems to be the physics problem of
PMD.".
This is not true for 10km SMF.
The 40Gbit/s PMD was a technical challenge in several years ago but now it
is not downside.
Even, we are discussing 1310-nm devices while current module includes
1550-nm devices.
(We can neglect dispersion issue in case of 1310nm transmission)
The biggest cost in current serial module is silicon chip that is much more
volume sensitive.
I hope you know the accumulative shipment of 40Gbt/s client module is around
10K peaces or such range.
However IEEE confirmed market of 40GbE 10km serial enough for
standardization, you can expect much lower cost with higher volume.
Also investment for 40Gbit/s transmission networks started these years, thus
industry started invest for 40Gbit/s technologies.
You will find much activity in the industry.
All
I am very concerning during the meeting and e-mail discussion,
many of members may misunderstand the 40Gbit serial technology status and
activity in the industry,
and understand only the surface.
We, who has technology especially optical device technology, should be
responsible to let people understand the technology.
I will think about it.
=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=
Atsushi Takai
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----- Original Message -----
From: "Jeff Meyer" <jmeyer@xxxxxxxxx>
To: <STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx>
Sent: Sunday, August 03, 2008 2:33 AM
Subject: Re: [802.3BA] Discussion on 40G for => 10 km SMF
Chris has a excellent point about
_Other Aspects_
It is no longer possible to simply increase Baud to match data rate,
because of fundamental electrical and optical propagation limits.
This was recognized during the 100G SMF PMD discussion, with Serial
never a viable alternative for the 10km or 40km reach. In the
future, all data rates beyond 100G will use some form of multi-lane
technology. 40G is the inflection point where cost and difficulty of
Serial rises dramatically compared to multi-lane alternatives.
Optical communication has reached the point that all other forms of
communication (wired or wireless) reached many years ago, where
simple modulation format serial solutions are not practical.
The biggest downside of 40G serial, seems to be the physics problem of
PMD. However there are an increasing number of long haul equipment
providers who have solved this problem. There have been thousands of 40G
serial long haul installations deployed to date.
As far as the Cost, Power, Size & Reliability I think this favors
serial. The cost saving of CWDM seems largely driven by the large number
of vendors providing 10G IC's and components. But let us ponder, if the
10GE fathers chose 4x 2.5G WDM to reduce risk in the late 1990's would
we be benefiting from the low costs and the large number of vendors? All
we need is multiple vendors of 40G serial components and the prices will
plummet. Lets face it the cost of SiGe is not that much higher than CMOS
unless you get to volumes greater than 100,000 parts. By then, CMOS
processes will catch up to SiGe in FT. I am a microwave guy and the 40G
packaging is not difficult these days ( there are many vendors that can
do LTCC fine line packages and they are "Open Tooled" so you can get a
reference design for the 40G electrical packages for no NRE ). If we
compare microwave packaging to flip chip mounting of lasers and optics,
I would imagine optics costs more, but I have no "hard data" to support
this.
The biggest reason why I favor serial over CWDM is the leadership for
the future. Lets take the risk like the 10G serial innovators did in the
late 90's. Once we get several manufacturers of 40G parts this prices
will plummet.
Schedule Risk. Albeit the risk for serial is higher but how much?
Let's keep technology moving forward for the future generations.
Jeff Meyer
Chris Cole wrote:
> Takai-san’s 7/31/08 email discusses a number of points. Our arguments
> concerning his first two points (Cost and Time to Market) are
> unchanged from cole_04_0708, so are not repeated here. The remaining
> points are addressed below.
>
> _Power_
>
> The long term power consumption of 40GE CWDM and 40GE Serial is
> similar. Four 10G un-cooled DFBs and associated Laser Drivers use
> about the same power as one cooled 40G EML and associated Modulator
> Driver. The remaining ICs are also about the same if advanced process
> nodes and new designs are assumed. As was pointed out by Joel Goergen
> during the Q&A session in Denver, a 40GE Serial block diagram has
> comparable circuitry to 40GE CWDM block diagram when drawn fairly to
> permit apples to apples comparison.
>
> There is no basis for a claim at this late stage in the debate that
> Serial has a power advantage over CWDM, and that CWDM “power reduction
> plans are invisible.” In jewell_03_0508, p.9 and again in
> traverso_02_0708 p. 12, ratios of power between an aggressive Serial
> implementation and CWDM implementation are 0.96 and 0.97, i.e. clear
> statements in pro-serial presentations that there is no advantage.
>
> _Size_
>
> For future generation products, CWDM has an advantage over Serial for
> fitting into a smaller form factor like QSFP because similar to a
> 10GE-LR SFP+, the re-timing CDRs can be moved outside of the module.
> Serial always has to have the 4:1 SerDes function in the module. Even
> with aggressive projections about future component size and power,
> Serial has a packaging and thermal management design challenge to fit
> into QSFP.
>
> What is required to fit 40GE CWDM into QSFP is optics integration.
> This type of technology has been described in numerous presentations
> to the HSSG and involves flip-chipping lasers onto a PLC with an
> integrated AWG Mux. The CWDM grid prevents use of a monolithic DFB
> array and requires flip-chipping discrete DFBs, but that is a yield
> and cost issue not a feasibility or size issue. The time line for such
> an advanced development program is lengthy, but is similar to
> realistic PCB RF-interconnect 40GE Serial development schedules. The
> investment required to bring this advanced technology to market is
> high, again similar to one required for low cost 40GE Serial.
>
> In contrast, no advanced technology development is required to quickly
> bring to market first generation low cost CWDM products based on
> discrete optics packaged in a larger form factor.
>
> _Reliability_
>
> There is no current 1310nm 10G DFB failure data that justifies
> bringing up concerns about the reliability of a 4x10G CWDM PMD. 10G
> 1310nm PMDs ship in volume today with very high reliability. If there
> is actual field failure data behind this concern, it would add
> credibility to have it presented.
>
> _Other Aspects_
>
> It is no longer possible to simply increase Baud to match data rate,
> because of fundamental electrical and optical propagation limits. This
> was recognized during the 100G SMF PMD discussion, with Serial never a
> viable alternative for the 10km or 40km reach. In the future, all data
> rates beyond 100G will use some form of multi-lane technology. 40G is
> the inflection point where cost and difficulty of Serial rises
> dramatically compared to multi-lane alternatives. Optical
> communication has reached the point that all other forms of
> communication (wired or wireless) reached many years ago, where simple
> modulation format serial solutions are not practical.
>
> Chris
>
>