Re: [10GMMF] Dynamic test (was: TP3 3-impulse test proposa)l
As I walked through a data center this morning with thousands of cables
(very many MMF), it was obvious to me that the major case for movement of
the fiber is the vibration caused by -- literally -- the 10's of thousands
of fans (yes, it is the case that a relatively small number of these affect
a specific fiber. I would guess this to be related to those that are most
closely coupled. There may be as many as 100 of these).
Based on the grab the cable or cable bundle test and become one with the
fiber, it seems that the majority of the vibration occurs at the connector
and within the first 10's of centimeters from the connector. This is not
what I first expected. It does make intuitive sense.
This vibration, of course, is continuous during the operation of the
equipment.
Presuming the vibration I can detect is sub 10KHz (more likely sub 1 KHz),
it represents a whole lot of bits per vibration period.
I have no way to validate this. But, I presume that since there is no
attempt to design it out there may well be a sampling of these that are
actually vibrating at a harmonic with respect to the cable/connector
assembly.
Ain't life fun.
jonathan
> -----Original Message-----
> From: owner-stds-802-3-10gmmf@IEEE.ORG
> [mailto:owner-stds-802-3-10gmmf@IEEE.ORG]On Behalf Of Lobel, Martin
> Sent: Tuesday, September 21, 2004 1:57 AM
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: Re: [10GMMF] Dynamic test (was: TP3 3-impulse test proposa)l
>
>
> Jonathan,
>
> I fully agree with your observations from the lab (moving the fiber
> several centimeters etc.) and the fact that building vibrations will
> only lead to minor movements of fiber.
>
> My comments are, however, a reflection of slide 11 of the TP3
> presentation sent out on the reflector on Sep. 17th by Ben Willcocks
> which suggests that we should use a dynamic test that shifts from
> post-cursor to pre-cursor at 1 KHz. I believe that this is not
> reproducing any real-life scenario and could be too stressful
> to the EDC
> solution.
>
> For a given installed fiber, I believe that two things can
> happen to the
> fiber/connector in a link:
>
> 1) The fiber undergoes vibrations due to building movements.
> 2) The fiber is moved (bend or twisted) by personnel during
> installation
> of other hardware, daily cleaning etc.
>
> My comment is related to 2) which can cause (in line with your
> observations in the lab) large changes in the channel impulse
> response.
> I don't know the nature of such changes but believe they can be large
> but with a longer time scale than vibrations (how fast can you move a
> fiber by hand). I believe that it is vital to study these
> nature of such
> large changes and ensure that any dynamic test covers the 2) case.
>
> I'm looking forward to the report out from the Task 2 to
> understand more
> about the physical behavior of the channel.
>
> Thanks,
> Martin
>
>
> **************************************************************
> *********
> Martin Lobel, M.Sc.E.E., Ph.D.
> Standards and Advanced Technology
> Intel Copenhagen ApS
> Mileparken 22
> DK-2740 Skovlunde
> Denmark
> Phone (direct): +45 44 54 61 33
> Cell phone +45 27 22 62 37
> i-net: 8-2966 133
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> Fax: +45 70 10 10 63
> email: martin.lobel@intel.com
> **************************************************************
> *********
>
> -----Original Message-----
> From: owner-stds-802-3-10gmmf@IEEE.ORG
> [mailto:owner-stds-802-3-10gmmf@IEEE.ORG] On Behalf Of Jonathan King
> Sent: 21. september 2004 01:48
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: Re: [10GMMF] TP3 3-impulse test proposal
>
> Hi Martin
>
> I have a comment on the TP3 dynamic response test.
>
> I expect that the TP3 dynamic test will need to be significantly below
> 1kHz rate if it is to be realistic.
>
> Task 2 is actively studying time variation effects, and is
> basing tests
> on GR-63-CORE which is an existing standard describing appropriate
> operational testing for in building environments. It describes
> vibration testing from 5Hz to 100Hz, with constant
> acceleration stimulus
> (0.1g and 1g accelerations). For constant acceleration, the
> amplitude of
> vibration decreases with the square of the frequency, for example:
>
> At 5Hz and 1g acceleration, vibration amplitude is 2 cm peak to peak,
> comparable to a rather fast fibre shaker as described in
> TIA/EIA-455-203;
> At 50Hz and 1g acceleration, vibration amplitude is 0.2
> millimetres peak
> to peak;
> At 500Hz and 1g acceleration, vibration amplitude is 2 microns peak to
> peak;
>
> I think its common experience in the laboratory that large changes in
> IPR occur only when a fibre coil is distorted by several centimetres,
> with relatively insignificant changes in IPR at displacements
> much below
> 1mm.
> I expect this will place an upper bound on the test frequency in the
> ~10Hz range
>
> best wishes
>
> Jonathan
>
> tel: 1 408 524 5110
> e-mail: jking@bigbearnetworks.com
> fax: 1 408 739 0568
>
> Jonathan King
> Director, Optical Systems
> BigBear Networks
> 345 Potrero Avenue
> Sunnyvale, CA 94085
>
>
> -----Original Message-----
> From: Lobel, Martin [mailto:martin.lobel@INTEL.COM]
> Sent: Monday, September 20, 2004 3:47 AM
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: Re: [10GMMF] TP3 3-impulse test proposal
>
> All,
>
>
>
> A)
> From a practical implementation point of view, it makes a lot of sense
> to limit the number of 'taps' to a minimum (three so far). As pointed
> out by Lew, I'm also concerned that the limited time span of the
> stressor (2xdT=200 ps) will not be a good emulation of real
> life channel
> impulse responses even that the PIE are alike.
>
> Many we should consider to have two tests with different dT(?). It
> could, e.g., be implemented with 5 taps total.
>
> B) Comments on the dynamic test: The biggest problem for real EDC
> solutions may not be to handle the ~KHz variation (1 KHz has been
> suggested) but more the problem of been able to handle the variety of
> channel responses and make the transition from one response 'A' to
> another channel response 'B' without causing errors.
>
> The question is if we can imagine that any given Cambridge channel
> response may be followed by any other arbitrary Cambridge Channel
> response due to vibration of the fiber and/or connectors. If
> the answer
> is 'no' then the suggested dynamic test of going from a state with
> completely pre-cursor only to a new state with completely post-cursor
> only may be a too stressful test that may lead to a non-desirable
> trade-offs for the implementation.
>
> Regards,
> Martin
>
>
>
> -----Original Message-----
> From: owner-stds-802-3-10gmmf@IEEE.ORG
> [mailto:owner-stds-802-3-10gmmf@IEEE.ORG] On Behalf Of Lew Aronson
> Sent: 17. september 2004 21:02
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: Re: [10GMMF] TP3 3-impulse test proposal
>
> I think this is very close to where we want to be for the dynamic
> penalty test, and I see no reason why the three impulse response
> functions can't be aligned with those used for the static test. A
> number of different comments:
>
> 1) We should do this calculation (and all similar
> calculations) for 300m
> as well as 220m.
>
> 2) It is interesting to come up with 1.0 UI for the dT. In a way that
> is good in that I know that many consider that a pretty
> demanding case,
> so if it makes sense with the fiber model and EDC makers consider it
> realistic to pass, than on that basis it might be a good choice.
>
> 3) I am concerned about deriving the details of the impulse response
> parameters solely from PIE metrics. The reason is that PIE is for an
> infinite ideal equalizer. As such, it's sensitivity to the total time
> span of the impulse response is presumably a lot flatter (and more
> non-monotonic) than is the performance of a real finite equalizer. I
> think we see this in that the final choice in the values was not
> terribly sensitivie to dT and was chosen to get a close fit on the PIE
> value for the -D and -L cases simulataneously.
>
> Thus, we risk coming up with a choice which is too short (compared to
> actual fiber response) to adequately stress a real implementation, or
> vice versa. Even worse, our choice is likely to drive the design
> tradeoffs of the EDC's used and thus should really match the dT spands
> from the fiber models.
>
> I would suggest that, at least in the case of the dT choice, that the
> fiber models and Petre's work be used to determine the approximate
> choice, and that we live with a larger difference in PIE-L and PIE-D
> that results.
>
> 4) With that said, I think the idea of having the same dT and the
> pre-cursor and post cursor symmetric to each other is probably a great
> goal for the static test as well and would then naturally align the
> static and dynamic tests. [This would not change my thinking
> on the fact
> that the static and dynamic tests should be seperate, I would
> still have
> many reasons to want that]. Petre's work so far has emphasized the
> goodness of fit to particular fiber examples. In the end, I think we
> just want to have something of the same general shape chosen to
> represent the 99% point by a combination of PIE value and
> represnetative
> dT values, and to use that extra freedom to have equal dT's between
> pulses and cases if at all possible.
>
> Thus, I would say that we want to wind up with something of
> the form Ben
> has given us, but with the dT and perhaps a value motivated more by
> Petre's work than by the most exact fit to PIE numbers.
>
> Lew
>
> Lew Aronson (lew.aronson@finisar.com)
> Finisar Corporation
> 1308 Moffett Park Drive
> Sunnyvale, CA 94089-1133
> 408-542-4215 (PH)
> 408-543-0083 (FAX)
>
>
> -----Original Message-----
> From: Ben Willcocks [mailto:ben.willcocks@PHYWORKS-IC.COM]
> Sent: Friday, September 17, 2004 8:13 AM
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: [10GMMF] TP3 3-impulse test proposal
>
>
> Further to the preliminary data I presented in the phone
> conference of 7
> September, I have attached slides showing our TP3 3-impulse test
> proposal & simulation results. Many thanks to Sudeep Bhoja for his
> assistance regarding the PIE calculations.
>
> With Mike's permission, I would like to talk through this during next
> Tuesday's TP3 conference call.
>
> Regards,
>
> Ben
>