RE: Equalization
Vipul,
Since you asked for my comments / suggestions (this is probably going to be
different than you expect):
1. I am in full support of Walt is trying to accomplish.
2. I posted a note regarding the September meeting and what is in order
given our objectives, schedule, etc. In that note, I implied that the
schedule was of highest priority and that we needed to keep things moving. I
now believe that this was an over-simplification. There are two highest
priority items. In short, we need to have a good solution in a timely
manner.
I presuppose that all of us have had discussions related to building a
product "right" or building the product "on time." The ideal is obvious. In
this instance, we know what "on time" means (there was a good one in Dilbert
yesterday on this). My sense is that Walt is attempting to see if we have
any consensus on what "right" means without getting into some unproductive
philosophical discussion.
Some standards bodies feel that they have succeeded if they can vote in a
"mutually disagreeable compromise." To me, this is an unacceptable outcome.
802.3 has had a rich history in dealing with these issues. For this reason,
it has developed (and I can think of no better measuring stick than) the 5
criteria. In this instance, Broad Market Potential; Technical Feasibility;
and Economic Feasibility seem to be most applicable to the question.
I would argue that virtually every point made to date regarding support of
MMF fits into one of these three buckets (and frequently spans 2 or 3). So,
if we are correctly targeting our input, why are we at in impasse? I think
there are two principal reasons:
1. Different people interpret the application of the 5 criteria (according
to their circumstance and perspective) in different ways. By way of EXAMPLE,
is it possible that economic feasibility might mean different things to an
equipment manufacturer and an optical transceiver manufacturer? Might it
mean the cost of a link to one, and the fully burdened cost over the life of
the product to the other?
2. Much of the data we have available to us is very "fuzzy."
Yes, there are other reasons -- such as the fact that we are not permitted
to share cost/price data -- but, these are not within our control. If anyone
can think of another one that is within our control, please speak up.
Per this note, I am asking Geoff if he can provide some perspective on
improving our understanding the 5 criteria.
Armed with that, how might we reduce the amount of "fuzziness" in the data
we are using for comparison?
jonathan
>-----Original Message-----
>From: Vipul Bhatt [mailto:vipul.bhatt@xxxxxxxxxxx]
>Sent: Friday, July 21, 2000 4:09 PM
>To: stds-802-3-hssg@xxxxxxxx
>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
>