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Re: [802.3BA] 802.3ba XR ad hoc next step concern


One topic that should be covered in this discussion of longer XR links
is increased connector loss.  If the link is longer, there is a higher
chance that the link goes through additional patch panels and the number
of connectors will likely exceed 4. In addition to having more
connections, the MPO connector typically has considerably more loss as
an LC connector which was the baseline for previous Ethernet optical

If anyone can collect some information on how these 150+ meter links are
layed out it would be very helpful.  From my reading of flatman_01_0108,
it shows that 10%+ of access-to-distribution and distribution-to-core
links fall between 100 meters and 300 meters.  It would be helpful to
understand these XR links that must be out there, but many people don't

I covered connector loss in kipp_01_0108 and recommended having an annex
that specified what the supported link distance would be with 3.0 dB of
connector loss.  Maybe 3.0 dB is too high, but 1.5 dB of connector loss
could easily be exceeded on a 200 meter link that winds its way through
multiple patch panels through the data center.     

One criticism of my presentation was that we should have a statistical
model of the connector loss and Jonathon King provided a nice
statistical analysis in king_01_0108 with up to 4 connectors. If these
XR links went through one more patch panel which usually adds 2 more
connections, the likely mean connector loss would be around 1.25 dB and
probably 30-40% of links would exceed 1.5 dB of connection loss.  If the
links went through an additional patch panel and was up to 8 MPO
connections, then the majority of links would have more than 1.5 dB of
connector loss.  When you consider that a 150 meter link has higher
fiber attenuation than the 100 meter link, the increased connector loss
could push these links into troubled waters.

It would be good to model the link with 2.0 dB of connector loss as well
as the higher fiber loss to get an understanding of how the link will
work under this likely XR condition.


-----Original Message-----
From: Swanson, Steven E [mailto:SwansonSE@xxxxxxxxxxx] 
Sent: Wednesday, August 27, 2008 1:24 PM
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3BA] 802.3ba XR ad hoc next step concern


According to data presented over the last several meetings, I would
offer the following:

100m over MMF: 1x
150-200m over MMF: 1.2x
10km over SMF 8-12x

The reason people still invest money in multimode fiber is because it is
the most cost effective optical choice for short lengths (< 300m) 

Best regards,


-----Original Message-----
From: Mikael Abrahamsson [mailto:swmike@xxxxxxxxx]
Sent: Wednesday, August 27, 2008 1:34 PM
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3BA] 802.3ba XR ad hoc next step concern

On Wed, 27 Aug 2008, Dove, Daniel wrote:

> Perhaps you can provide a chart that shows the distribution of lengths

> and the relative costs associated with them, and we can use that as 
> the basis for further understanding? I know that this data has been 
> presented in various presentations, but a nice succinct chart would be

> helpful.

I'm also interested in the cost difference between 100m, cost for an MM
optic that'll do 150-200m, and if the optic that does 10km over SMF is
applicable for the 200m MM case (like it is with 10GBASE-LX4 and
1000BASE-LX for instance), and if it is, what's the relative cost with
that included.

On a personal note, I still don't understand why people invest a lot of
money in MM cabling when SM is around :P It's obvious that to use MM
with price-efficient optics, each hike in speed seems to shorten the
reach in MM fiber.

Mikael Abrahamsson    email: swmike@xxxxxxxxx