RE: Patch cord for 1300 WWDM
Dave,
I would like to make it clear that 850nm CWDM does not require any special
launches to achieve the 100m (installed) and the 300m (MMF) objectives. Per
Paul Kolesar's previous email, an overfilled launch on new multi-mode fiber
results in a minimum bandwidth of 500MHz.km, which equates to 300m for 850nm
CWDM. Installed 50 micron fiber also has a minimum bandwidth of 500MHz.km,
which equates to 300m for 850nm CWDM.
As you indicated, 850nm CWDM has a lower cost than the 1300nm WWDM. In
addition to the tolerance differences you mentioned, the 1300nm lasers and
multiplexer have a higher cost than those required for 850nm CWDM. Lastly,
there is never a patch cord required for 850nm CWDM.
In summary, 850nm CWDM is a multi-mode optimized solution for the 100m and
300m objectives.
Eric Grann
Blaze Network Products
-----Original Message-----
From: owner-stds-802-3-hssg@xxxxxxxx
[mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Dave Dolfi 3764
Sent: Friday, August 04, 2000 12:21 PM
To: stds-802-3-hssg@xxxxxxxx; pkolesar@xxxxxxxxxx
Cc: dave_dolfi@xxxxxxxxxxx
Subject: RE: Patch cord for 1300 WWDM
Dear Paul,
I had a feeling I'd hear from you on this, and you didn't disappoint
me! Thank you for your detailed response. You seem to be saying
two things. First, you describe what is basically a doughnut shaped
launch which will both satisfy the launch requirement for the new fiber
to achieve greater than its OFL bandwidth, and at the same time,
guarantee that the OFL bandwidth is achieved on the installed base
of 62.5 um MMF. However, you also seem to be saying that it doesn't
matter anyway, since ANY launch will achieve the OFL bandwidth on the
62.5 um installed base. (I assume that you are only referring to SX,
since if it were true for LX as well we wouldn't need patch cords).
With respect to your first statement, I would reply that the launch
you describe can certainly be classified as a "conditioned" launch.
I don't think it could easily be achieved with multiple sources,
at least not with the kind of simple multiplexers which have been
proposed by companies such as Blaze and Agilent. I also question
whether the tolerances required by such a launch would allow the
loose, multimode type tolerances which the 850 nm CWDM advocates have
claimed for this PMD, and which form the basis of their claim of
lower cost relative to 1300 nm WWDM. If this launch is really
necessary for 850 nm CWDM to work, then these questions need to
be addressed.
With respect to your second statement, I would refer you to the work
that was done by Agilent (HP at the time) during the DMD studies of
802.3z, particularly the presentation to 802.3z by Lewis Aronson at
the March, 1998 meeting of 802.3z (available at the following URL:
http://grouper.ieee.org/groups/802/3/z/public/presentations/).
There are measurements presented there on both 62.5 um and 50 um
MMF at short wavelength. I'm not in a position to challenge your
assertion regarding the absence of launch restrictions at short
wavelength (you're the expert here!) but I would appreciate it if
you look over this paper and verify that the results presented are
consistent with your statement.
Dave Dolfi
Agilent Technologies
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> From: "Kolesar, Paul F (Paul)" <pkolesar@xxxxxxxxxx>
> To: stds-802-3-hssg@xxxxxxxx
> Subject: RE: Patch cord for 1300 WWDM
> Date: Fri, 4 Aug 2000 11:42:30 -0400
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>
> Dave Dolfi,
>
> I would like to address your concerns over launch conditions.
>
> The launch requirement for the new 50 um fiber is presently specified as
>=
> 85% encircled flux within a 16 um radius of the center of the fiber. This
is
> not much different than the launch requirement determined to be optimal
for
> enhanced 62.5 um fiber which is <= 25% encircled flux within 4.5 um radius
> and >= 75% within 15 um radius of the center of the fiber. The main
> difference is that the 62.5 um spec limits the amount of power allowed in
> the very center of the fiber (within 4.5 um radius) while the 50 um spec
has
> no such limitation. But, the similarity of the outer radii specification
> (85% within 16 um vs 75% within 15 um) permits solutions that meet both
> requirements simultaneously. In short, the overall power concentration in
> the center of the 50 um fiber is not required to be much different than
that
> for enhanced 62.5 fiber.
>
> Further, the TIA FO2.2 data indicates launches that meet the above
> requirements for enhanced 62.5 um fibers do not cause degradation of the
> bandwidth below the OFL specification on installed-base 62.5 um fibers. In
> fact, such launches usually cause bandwidth enhancement. By combining
these
> launches with 62.5 um fibers tested and determined to produce higher
> restricted launch bandwidth, we can guarantee enhanced performance.
Perhaps
> even more to the point, the data collected by both the TIA and IEEE on
this
> subject has not shown any launch condition that caused the bandwidth to
> collapse below the 160 MHz-km OFL spec for 62.5 um fiber. This includes
> launches produced by single-transverse mode "CD" lasers as well as
> multi-transverse mode VCSELs with various spot sizes and numerical
> apertures. It also includes Radial Overfilled Launches that were developed
> as a possible test launch condition by the IEEE MBI study group, which are
> said to extract the "worst case" modal bandwidth for any laser launch. In
> summary, there is no evidence of any launch condition that causes less
than
> 160 MHz-km bandwidth from the installed base of 62.5 um fiber. The 100 m
> capability of the 850 CWDM PMD is based on 160 MHz-km bandwidths.
>
>
> Regards,
> Paul Kolesar
>
> ----------
> From: Dave Dolfi 3764 [SMTP:dolfi@xxxxxxxxxxxxxxxxxxxxxxxx]
> Sent: Thursday, August 03, 2000 6:17 PM
> To: stds-802-3-hssg@xxxxxxxx; billw@xxxxxxxxxxx
> Cc: dave_dolfi@xxxxxxxxxxx
> Subject: RE: Patch cord for 1300 WWDM
>
>
> Dear Bill,
>
> I'm happy that you agree with my summary of the patch cord
> situation.
> Unfortulately, I'm not sure that I agree with everything you seem
> to be saying about 850 nm CWDM. Specifically, while I agree that
> you could specify a VCSEL and a mux design which would achieve 100
> meters on the installed 62.5 um MMF OR > 550 meters on the new
> enhanced
> bandwidth 50 um MMF, I'm not sure that a single design could achieve
>
> both at the same time.
>
> The 62.5 um conventional fiber requires a large spot at its input to
> mitigate potential DMD problems if too much of the excitation is in
> the central portion of the fiber, while the new fiber requires a
> small spot centered at its input in order to satisfy the encircled
> flux
> requirement necessary to achieve the higher bandwidth. Can you
> really
> achieve both of these at the same time?
>
> I think you need to prove that this is true before you can claim to
> simultaneously achieve the bandwidths you are claiming over both
> fiber
> types.
>
>
> Dave Dolfi
> Agilent Technologies
>
>
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> > Reply-To: <billw@xxxxxxxxxxx>
> > From: "Bill Wiedemann" <billw@xxxxxxxxxxx>
> > To: <stds-802-3-hssg@xxxxxxxx>
> > Subject: RE: Patch cord for 1300 WWDM
> > Date: Thu, 3 Aug 2000 10:38:21 -0700
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> >
> >
> > Thank You.
> > Everything you say is correct. 850CWDM has been designed to
> directly meet
> > the 100 meter objective over installed (DMD challenged) 62.5u MMF
> and the
> > 300m objective over MMF. In addition we can meet 300 meters over
> existing
> > 50 micron fiber and greater than 550 meters with the new high
> bandwidth MMF.
> >
> > Finally experimental evidence has shown greater than 300 meter
> performance
> > over installed 62.5 micron fiber that is not DMD challenged.
> >
> > Bill Wiedemann
> > Blaze
> > 925-560-1610 x169
> >
> > At 02:11 PM 8/2/00 -0700, David W Dolfi wrote:
> >
> >
> > >Everyone,
> > >
> > >
> > >There seems to have been some confusion at the La Jolla
> > >meeting over the necessity for an offset patch cord for
> > >1300 nm WWDM. Because of this, and additional comments
> > >made on the reflector since the meeting, I am writing
> > >this email to clarify the situation.
> > >
> > >Fact 1. An offset patch cord is NOT required for 1300 nm
> > >WWDM in order to meet the current MMF objectives of 802.3ae.
> > >That is to say, it is NOT required in order to achieve a 100
> > >meter link length on the installed base (this includes both
> > >62.5 and 50 um standard MMF, which both have a 500 MHz-km OFL
> > >bandwidth length product at 1300 nm), NOR is it requred to
> > >achieve a 300 meter link length on the new enhanced BW
> > >MMF, which also has a 500 MHz-km OFL bandwidth at 1300 nm.
> > >
> > >Needless to say (but I will for the sake of completeness)
> > >1300 nm WWDM also supports single mode fiber up to 10 km,
> > >again without a patch cord.
> > >
> > >
> > >Fact 2. The ONLY time you need to use a patch cord with
> > >1300 nm WWDM is if:
> > >
> > >1. You want to extend the link length of the MMF installed base
> > >to 300 meters
> > >
> > >AND IN ADDITION TO THIS
> > >
> > >2. The fiber in question is "DMD challenged".
> > >
> > >
> > >Please note that if you are in this particular situation, none
> > >of the 850 nm based PMDs will satisfy your need, patch cord or
> > >not (but see Note below). Your only alternative in this
> situation,
> > >with an 850 nm PMD, is to install new fiber, either the enhanced
> BW
> > >multimode fiber or single mode fiber. Therefore, the notion that
> > >the patch cord is some sort of "penalty" you pay for using 1300
> nm
> > >WWDM is really the wrong way to think about it. Rather than a
> > >shortcoming, it is actually a benefit, since it gives you the
> (rel-
> > >atively speaking) low cost option of using a patch cord in a sit-
> > >uation where your only other alternative is to pull new fiber.
> > >
> > >Note: The 850 nm 4 channel CWDM PMD will allow you a 300 meter
> link
> > >length, without a patch cord, on the installed base of 50 um
> fiber
> > >ONLY. However, this is a small benefit, since the great majority
> > >of the MMF installed base is 62.5 um fiber, on which 850 nm CWDM
> > >will only support a 100 meter link length (due to the fact that
> > >62.5 um fiber has an OFL bandwidth length product of only 160
> > >MHz-km at 850 nm).
> > >
> > >
> > >David Dolfi
> > >Agilent Technologies
> >
> >
>