RE: Equalization
Vipul, Thanks for kicking off and helping to moderate the equalization
discussion. I think you have come to some great conclusions.
I would like to point out that 850CWDM will also benefit from equalization
and encircled flux efforts.
The main differences are as follows:
850CWDM already directly meets both the 100 meter and 300 meter distance
objectives. WITHOUT equalization, WITHOUT any special launch and WITHOUT an
offset launch patch cord
i.e. 850CWDM meets 100 meters over legacy 62.5 micron fiber (DMD bad 160
MHz.km)
i.e. 850CWDM meets 300 meters over 50 micron fiber (500 MHz.km)
Any efforts to include equalization or encircled flux launches in PMDs will
show greater benefit at data rates of 3.125 then they will at serial rates
of 10.3125.
Possibly even more important is it is much easier to design equalization
schemes that work at 3.125 baud rates versus schemes that must work at
10.3125.
My recommendation is that those who would like to propose equalization and
encircled flux do so prior to or coincident with the next interim meeting in
Boston. Also I recommend they contact the influential and respected members
of the committee to understand what these key members will need to see to
approve equalization and restricted launch.
I support this effort and will help wherever possible, as 850CWDM could
easily meet 300 meters over legacy 62.5 micron fiber with less performance
than serial solutions would need. i.e. less risk, lower power.
I am concerned about encircled flux being included as David Cunningham from
Agilent spoke out very negatively against this. I recommend anyone who is
going to be proposing solutions with encircled flux contact David prior to
proposing at the interim meeting.
Bill
-----Original Message-----
From: owner-stds-802-3-hssg@ieee.org
[mailto:owner-stds-802-3-hssg@ieee.org]On Behalf Of Vipul Bhatt
Sent: Friday, July 21, 2000 4:09 PM
To: stds-802-3-hssg@ieee.org
Subject: RE: Equalization
Dear colleagues,
Okay, so where are we? Let me review what I think I have heard so
far.
Yes, the idea of 10G Serial on installed MMF is interesting, but
there are a couple of holes in the proposal, including bad timing.
Here is the summary, followed by holes.
850 nm Serial solution:
-----------------------
- Will benefit from TIA FO 2.2 Encircled Flux and Restricted Mode
Launch work.
- Offset Launch jumper not required.
- Start with 385 MHz-Km bandwidth assumption on installed MMF.
- Add 6 dB equalization to support 100 meters operation, additional
9.54 dB to support 300 meters. Equalization has to be adaptive, in
the sense that impulse response will be different for each link. It
must overcome severe DMD in some cases. With Encircled Flux launch,
for a given link, the impulse response will not vary significantly
with time, so it can be assumed as time-invariant or very slowly
varying in time.
- Potentially, end up with a total of 3 PMDs that meet all 5
Objectives.
1310 nm Serial solution:
-----------------------
- Will benefit from EMB work done with 802.3z.
- Offset Launch jumper is required.
- Start with 500 MHz-Km bandwidth assumption on installed MMF.
- Add 4 dB equalization to support 100 meters operation, additional
9.54 dB to support 300 meters. Equalization has to be adaptive in
the sense that impulse response will be different for each link. It
must overcome severe DMD in some cases. With offset launch, for a
given link, the impulse response will not vary significantly with
time, so it can be assumed as time-invariant or very slowly varying
in time.
- Potentially, end up with a total of 2 PMDs that meet all 5
Objectives.
List of holes:
-------------
1. It hasn't been established that Encircled Flux over a randomly
selected fiber from installed base will ensure 385 MHz-Km bandwidth
(850 nm) with a high degree of statistical confidence. Gair's
suggestion of tagging an RML-compliance condition is one possible
solution. We need to know if that suggestion will be acceptable to
802.3ae end users and system integrators.
2. It hasn't been established that 10G equalization is feasible. By
feasible, I mean something like - a demonstrable solution before the
Working Group Ballot, capable of overcoming severe DMD, consuming
less than 3 watts, with a cost comparable to that of other
components, backed by technical presentations in September that
instill a high degree of confidence in the 802.3ae members.
3. Perhaps it is too late. There is a high likelihood that at the
September Interim, motions to adopt other PMDs that meet Objectives
1 and 2 will pass.
Hole 1 can be bypassed by adopting a 1310 nm Serial solution. Hole 2
can't be plugged until we have heard presentations from DSP experts
in September. Hole 3 is the most regrettable. I don't know how to
plug it. Jonathan, Walt, do you have any comments or suggestions?
Thanks,
Vipul