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
Please respond to
Chris Cole <chris.cole@FINISAR.COM>
To
STDS-802-3-HSSG@listserv.ieee.org
cc
Subject
Re: [HSSG] The List
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.
"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.