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RE: Re[2]: 1310nm vs. 1550nm -> Eye Safety + Attenuation


Regardless of whether a 1550 would meet the eye safety recommendations I
would strongly recommend that a protocol be established to turn off the
laser in the event off a fiber cut.  Network operators routinely add
pre/post amps to boost the laser power and range.  So although the original
laser may meet safety requirements, the output of the laser at the other end
may not.

However, as I suggested before, I think it is also important not to depend
on a signaling protocol that assumes no Rx path. In CA*net 3, we use a
propriety out of band signaling system for laser safety and network
management.  My humble suggestion is that we use the IP layer for out of
band management and signaling.


Bill St Arnaud
Director Network Projects



> -----Original Message-----
> From: bgregory@xxxxxxxxx [mailto:bgregory@xxxxxxxxx]
> Sent: Thursday, May 06, 1999 12:32 PM
> To: David W Dolfi; Bill St. Arnaud
> Cc: stds-802-3-hssg@xxxxxxxx; dolfi@xxxxxxxxxx; twhitlow@xxxxxxxxx
> Subject: Re[2]: 1310nm vs. 1550nm -> Eye Safety + Attenuation
>      In response to Bill's email... regarding the EDFA issue, I'd imagine
>      that this would only be used in a small number of cases with
> a serial
>      10GbE approach.  I don't think it needs to be a core concern of the
>      group, but in some dark fiber trunking applications it can
> be useful.
>      I am most concerned about wavelengths vs. eye safety, and
> wavelengths
>      vs. fiber attenuation.  This could end up being a real killer.  Four
>      lasers @ 850nm or 1310nm put out quite a bit of light in an eye
>      sensitive range.  As I remember, four lasers at 1550nm offer a lot
>      more margin.  A single source at 1550nm could be very strong
> and still
>      meet the eye safe requirements.  This increase in power
> combined with
>      lower fiber attenuation would reduce some of the link distance
>      problems that we're bound to run into.
>      Also, long term I can't see how [4 lasers and an optical mux] + [4
>      photodiodes and an optical de-mux] would be better than a single
>      source and photodiode.  There is a lot of difficult
> packaging involved
>      in the CWDM approach.  I think the CWDM solution offers a
> quicker path
>      to market because most of that technology is available
> today. But long
>      term a single 10 Gb source (uncooled DFB without isolator) has a lot
>      of advantages.  It is intrinsically much simpler.  I think the board
>      layout and chip-sets will eventually support this as well.  If the
>      standard wanted to be able to scale beyond 10 gigs, even the serial
>      10Gb solution could allow further CWDM scaling.
>      Regards,
>      Bryan Gregory
>      bgregory@xxxxxxxxx
>      630/512-8520
> ______________________________ Reply Separator
> _________________________________
> Subject: RE: 1310nm vs. 1550nm window for 10GbE
> Author:  "Bill St. Arnaud" <> at INTERNET
> Date:    5/6/99 10:38 AM
> Hmmm.  I just assumed that 802.3 HSSG would be looking at 1550
> solutions as
> well as 1310 and 850
> I agree with you on longer haul links it makes a lot more sense
> to operate
> at 1550
> I am not a big fan of EFFA pumping.  It significantly raises the overall
> system cost. It only makes sense in very dense wave long haul systems
> typically deployed by carriers.
> CWDM with 10xGbE transcivers should be significantly cheaper.  That is
> another reason why I think there will be a big market for 10xGbE with all
> those transceivers every 30-80km on a CWDM system. However there is a
> tradeoff.  There is greater probablity of laser failure with many
> transceivers and the need for many spares.  I figure somewhere
> between 4-8
> wavelengths on a CWDM and transceivers is the breakpoint where it is
> probably more economical to go to DWDM with EDFA. Also EDFA is
> protocol and
> bit rate transparent.
> An EDFA will ..(edited).....  But EDFA window is very small, so
> wavelength
> spacing is very tight requiring expensive filters and very stable,
> temperature compensated lasers at each repeater site.  Also laser
> power has
> to be carefully maintained within 1 db otherwise you will get
> gain tilt in
> EDFAs. A loss of a signal laser can throw the whole system off,
> that is why
> you need SONET protection swicthing. But companies are developing
> feedback
> techniques to adjust power on remaining lasers to solve this problem.
> A single 10xGbE transceiver will .(edited)....??? Probably less.  So 6
> 10xGbE transceivers will equal one EDFA.  No problems with gain tilt.  If
> you lose one laser you only lose that channel, not the whole system.
> Protection switching not as critical, etc
> Bill
> -------------------------------------------
> Bill St Arnaud
> Director Network Projects