Re: [HSSG] The List
Petar;
I feel
EDC in general term could mean alot of things to alot of people, and its
power consumption could range from 0 (passive EQ) to over 5-6W
and it could be implemented on the Rx side or Tx side. Not sure
what kind of EDC you meant, which simply did nothing
but degrade your HPC apps.
As to
the xtalk, what I meant was the electrical ones into the EDC
input because of multi-10G PMD lanes which may
originate from electrical or optical sources.
Chris;
The
extra EDC margin of 2-3dB I talked about comes from the efficient bandwidth
equalization/optimization mainly to the RX frond-end in front of the
decision circuit as you can see from a couple of ofc papers we posted.
Typically because of TOSA or ROSA flex circuits, bonding wires, PCB
trace etc associated with large area 10G MMF detectors,
the resultant RX frond-end bandwidth could be as low as 3-4GHz away
from the ideal BW of 7-8GHz, such bw reduction degrades the RX
sensitivity dramatically.
From the calculated curve of
varying the Rx frond end BW on the Q-function, the Q-factor roll of
quickly after 6GHz to 3GHz without EDC. When EDC is used to optimized
the bandwidth, the Q-curve could be very flat down to
2.5GHz. We also test some commercial ROSAs, I see sometimes this
margin could be well over 2-3dB.
Frank
Chris,
I agree with your assessment. If
nothing else, the EDC would add to the power consumption of the module, making
things worse for some applications, like HPC.
Frank, is the crosstalk you are talking about of
electrical or optical nature, and where does it occur?
Thanks,
Peter
Petar
Pepeljugoski
IBM Research
P.O.Box 218 (mail)
1101 Kitchawan Road,
Rte. 134 (shipping)
Yorktown Heights, NY 10598
e-mail:
petarp@us.ibm.com
phone: (914)-945-3761
fax:
(914)-945-4134
| Chris Cole
<chris.cole@FINISAR.COM>
07/02/2007 02:00 PM
|
Please respond
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Chris Cole
<chris.cole@FINISAR.COM> |
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| Re: [HSSG] The
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Frank,
I would be very interested to see your calculations
showing how one gets 2-3dB of extra margin through the use of an EDC for 10G
NRZ optical signal sent over 100m of OM3 MMF (typical BW at 850nm of
2000MHz/km.)
With respect to EDC for use with "low-cost" optics, I
characterized that as speculative, not
enabling.
Chris
-----Original Message-----
From: Frank Chang
[mailto:ychang@vitesse.com]
Sent: Monday, July 02, 2007 10:52 AM
To:
Chris Cole; STDS-802-3-HSSG@listserv.ieee.org
Subject: RE: [HSSG] The
List
Chris;
I personally agree EDC maynot help reduce or
mitigate cross-talk, instead will provide extra (2-3dB) margin/yield due to
e.g. band limiting effects or dispersion effects if any, existing in OE and EO
conversions or the fiber medium. While this extra margin can be used to
compensate for any penalty induced by xtalk. Like you said, also this could
enable the use of low-cost optics.
Frank
-----Original
Message-----
From: Chris Cole [mailto:chris.cole@finisar.com]
Sent:
Thursday, June 28, 2007 6:10 PM
To:
STDS-802-3-HSSG@listserv.ieee.org
Subject: Re: [HSSG] The
List
Ali,
It is not clear what problems are solved by your
proposal to define the 40G and 100G MMF optical specifications around linear
interfaces and host EDC.
Fist, SFP+ 10GE-SR optics are a solved problem
today, and the SFP+ 10GE-SR specification, while not optimum, is complete and
manufacturable. The original 300m meter 802.3 10GE-SR specification has a
number of issues which affect yield and therefore delayed the availability of
low cost 10GE. However, as has been seen from numerous emails on this
reflector, multiple manufacturers have resolved these issues.
On the
other hand, the SFP+ 10GE-LRM linear specification still has a number of
difficult issues to resolve. So you are proposing to consider as a starting
point a spec which is still under discussion and therefore not done, instead
of a specification which is complete and verified to work.
The reason
for going to a lower distance for 40G and 100G is to provide additional
margin/yield. Further, 300m multi-ribbon applications are highly unlikely, so
it makes little sense to have the 40G or 100G specifications driven by an
insignificant fraction of the applications. We may re-visit whether 100m is
the right distance (150m has been mentioned as an alternative,) but 300m would
be of little value as was commented on by multiple-end users during the HSSG
discussion of the MMF objective.
Second, I am at loss as to how an EDC
solves the additional penalty issue of cross-talk in a multi-lane application.
Cross-talk problems are solved through echo-cancellers, not EDCs. So if we
wanted to reduce cross-talk effects through signal processing techniques, a
solution resembling 1000BASE-T or 10GBASE-T would be required. 10GBASE-T power
numbers in the many watts have been reported on this reflector. For 40G, we
would expect linear scaling in power, and quadratic scaling for full-cross
ten-lane echo-cancellation. We will be well served to view this as a solution
of last resort, not as a starting point.
Third, I do not see the
motivation to have an EDC for an objective which explicitly states OM3 as the
fiber. OM3 does not have dispersion problems over a distance of 100m or 150m.
LRM EDC was developed for legacy OM1 fiber, already deployed within buildings,
for example between floors. I have heard no application identified in any HSSG
presentation for 40G or 100G which would use ribbon-fiber that had dispersion
problems like OM1. So we would burden 40G or 100G hosts with an EDC per
channel, so that we can use optics that do not meet SR specs on the
speculatively assumption that they are lower cost.
Fourth, cross-talk
for connectors and PCB traces has been simulated and quantified (see for
example page 12 of cole_01_1106.pdf.) There is no indication that the
cross-talk magnitude is anywhere near requiring the drastic measures of an
EDC/Echo Canceller. A careful re-allocation of the SFI (SFP+ interface) jitter
budget between the host and optics will permit tolerance of these levels of
cross-talk.
Missing is the measurement data for cross-talk in
multi-lane 10G I/O CMOS ASICs. Until we have solid data for this, we will not
be able to complete the specification of MMF PMDs that do not require
CDRs.
I would encourage all IC vendors participating in the HSSG, who
have developed silicon that implements 10G I/O, to bring in multi-lane 10G I/O
cross-talk data so that we can base the 40G and 100G specifications on
measurement
results.
Chris
----------------------------------------------------------------------------
"Ali
Ghiasi" <aghiasi@broadcom.com>
06/27/2007 12:33 PM
To: "Jack
Jewell" <Jack.Jewell@PICOLIGHT.COM>, "Paul Kolesar"
<pkolesar@systimax.com>
cc: STDS-802-3-HSSG@listserv.ieee.org
Subject: Re: [HSSG] The List
Jack and Paul
The question is
not whether SFP+ can achieve 300 m SR reach similar to XFP, but how do we get
to 10G SFP+
at 2.5x the cost of 1G classic SFP for DCE (Data Center
Ethernet) with max reach of 100 m.
If we can get to 10G SFP+ at 2.5x
the cost of 1G at 300 m then the 10G PAR objective is complete, but how
long
do we wait the need is know. But I do know the combination of
lower cost optics with EDC can deliver
the 2.5x cost objective for DCE
applications near term. To get to these cost the transmitter very likely
will not be fully SR compliant and in that case it does not matter if the
reach is 100 or 300 m.
The current assumption in the HSSG is that you
can achieve SFP+ limiting performance with 4 or 10 channels without the
use
of CDR in the module, with more crosstalk, less optimum layout, SerDes having
more jitter and less tolerance compare
to small port count PHYs, optics
??? You will get small benefit from reducing fiber reach to 100m but not
enough to close the
link budget. As Dan mentioned EDC is becoming a
standard feature on PHYs and we definitely need to leverage it for 40G/100G.
Use of linear interface is an approach that can close the link
budget without the use of CDR in the module, relax the optics
specifications, and the same interface can support passive copper Twin-ax
up to 10m.
Ali