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RE: PMD discussion




Dear Seto,

Yes, we did spend several years working on 850-nm WWDM, and demonstrated
4x2.5 Gb/s about 2 years ago in our lab.  As with the long wavelength WWDM
vs. Serial debate, I believe that 850nm-WWDM will be cheaper in the short
term than 850-nm serial.  The VCSEL and electronics technology for 2.5-Gb/s
are already mature and very low-cost. Also, the 4-1 electronic MUX will not
be needed in the WWDM approach. 

With the current FDA eye-safety requirements, it will be nearly impossible
to make an 850-nm WWDM module which meets Class I eye safety, without using
open fiber control.  The expectation is that the FDA will soon raise the
limit quite substantially, opening up the possibility of Class I safe 850-nm
WWDM modules.

By the way, WWDM and CWDM are exactly the same thing.  I know its convenient
to use WWDM for 1300 nm and CWDM for 850 nm, but this is completely
arbitrary.  I personally always refer to the approach simply as WDM.

Best Regards,

Brian Lemoff

> -----Original Message-----
> From: Seto, Koichiro [mailto:seto@xxxxxxxxxxxxxxxxxxxx]
> Sent: Monday, May 29, 2000 11:43 PM
> To: stds-802-3-hssg@xxxxxxxx
> Subject: Re: PMD discussion
> 
> 
> 
> [Date: 05/29/2000  From Seto]
> 
> Dear Brian,
> 
> Thanks for your clarification.  I look forward to your 
> evaluation result in 
> July.  I'm sure you are aware that I'm not at all against 
> 1310nm-WWDM proposal.
> 
> BTW, I assume your team has a lot of experience with 
> 850nm-WWDM solution.  I 
> believe you once had a 850nm-WWDM lab prototype (per Mr. 
> Dolfi's presentation 
> in 3/1999).  Would you provide your insight on the argument 
> on 850nm-serial vs.
>  850nm-WWDM?  Do you think there would be a potential laser 
> eye safety issue 
> in 850nm-WWDM proposal as suggested by Jonathan?  
> 
> Seto
> 
> > 
> > Dear Seto,
> > 
> > No offense taken.  There should be no problem going 10 km 
> over single mode
> > fiber with the same module that is optimum for going 300 m 
> over MMF.  I
> > expect that a full set of link results will be presented in 
> July, to provide
> > the physical evidence you are looking for.  Until then, 
> you'll have to trust
> > the link model.
> > 
> > 
> > As for relative cost, most people believe that WWDM will be 
> cheaper than
> > serial in the short term and that in the long run, serial 
> will be cheaper.
> > The debate seems to be over when the two will cross. Some 
> believe it will be
> > as soon as 2 years from now, while others believe it will 
> be 3 or 4 years
> > from now.  The 1.8x and 3.0x numbers you are referring to 
> have no basis,
> > other than an unscientific survey among a very small sample 
> (I believe the
> > number of survey respondents was 4) of serial PMD advocates.    
> > 
> > Since companies that are actually developing serial and 
> WWDM products for
> > sale usually choose to keep their cost models to 
> themselves, it will be
> > difficult to establish relative cost until products hit the 
> market.  Even
> > then, selling price and cost are two different things!
> > 
> > - Brian Lemoff
> > 
> > -----Original Message-----
> > From: Seto, Koichiro [mailto:seto@xxxxxxxxxxxxxxxxxxxx]
> > Sent: Monday, May 29, 2000 7:25 AM
> > To: wthirion@xxxxxxxxxxxx; stds-802-3-hssg@xxxxxxxx
> > Subject: Re: PMD discussion
> > 
> > 
> > 
> > [Date: 05/29/2000  From Seto]
> > 
> > Walter,
> > 
> > My understanding is that the following set is also one of 
> the top favorites:
> > 
> > ________________optimized for	may be used for
> > 1310 nm WWDM	MMF upto 300m	SMF upto 10km
> > 1310 nm Serial	SMF upto 10km	MMF upto 86m
> > 1550 nm Serial	SMF upto 40km	
> > ________________
> > 
> > 
> > I understand there are some risks that 850nm-WWDM solution 
> may not satisfy 
> > laser eye safety as Jonathan pointed out in the discussion 
> on Thursday.  
> > Also, I learned that there are some risks that 1310nm-WWDM 
> may not be able 
> > to achieve 10km at SMF if not impossible.  At least we have 
> not seen any 
> > data that would prove the feasibility of 1310nm-WWDM over 
> 10km SMF.  It is 
> > not to say that this can not be done, but I have not been 
> convinced that the
> >  same 1310nm-WWDM optics at same cost factor will serve for 
> both 300m MMF 
> > and 10km SMF.  Also, some people pointed out that 
> 1310nm-Serial can be built
> >  at cost factors of x1.8 to 850nm-Serial while 1310nm-WWDM 
> is x3.  If we can
> >  achieve the same goal (SMF 10km), the cheaper is the better.
> > 
> > I hope no one is offended by my not-so-educated opinion.  I 
> would appreciate
> >  a healthy discussion.
> > 
> > Seto
> > 
> > > 
> > > First of all, thanks to everybody that presented PMD 
> proposals at the last
> > > meeting. I've sent my presentation to David Law, so it 
> should be available
> > > on the web site in the next couple of days.
> > > 
> > > In listening to the discussion after my presentation and 
> then going around
> > > and talking to people, it feels to me like we're starting 
> to converge. Not
> > > there, yet, but making progress.
> > > 
> > > The equipment manufacturers made it pretty clear they 
> would like to see no
> > > more than 3 PMDs in the standard. The PMD vendors have 
> some concern that
> > > using only 3 PMDs may sub-optimize certain objectives, 
> however, they could
> > > support the 3 PMD position if it is made clear which 3 
> PMDs the equipment
> > > oems want.
> > > 
> > > Based on an informal straw poll and anecdotal evidence, 
> my opinion is the
> > > first choice would be the set:
> > > ________________
> > > 850 nm WWDM
> > > 1310 nm WWDM
> > > 1550 nm Serial
> > > ________________
> > > 
> > > If that set isn't feasible, then the 2nd most popular choice is:
> > > ________________
> > > 850 nm WWDM
> > > 1310 nm Serial
> > > 1550 nm Serial
> > > ________________
> > > 
> > > Thoughts, feedback?
> > > 
> > > Walt
> > > ___________________
> > > Walter Thirion
> > > Chair, IEEE 802.3ae PMD Sub-Task Force
> > > 301 Congress Ave.
> > > Suite 2050
> > > Austin, Texas 78701
> > > Voice:	512-236-6951
> > > Fax:	512-236-6959
> > > wthirion@xxxxxxxxxxxx
> > > ___________________
> > > 
> > > 
> > > 
>