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Re: [802.3BA] Reach Objective for MMF

your points on the distance needs of LANs and larger data centers resonate well with me.  I have viewed the 100m objective as a target that could be cost-effectively exceeded, but also one that could get sufficient support to be accepted as an objective by the HSSG and 802.3.  Now we have seen at least one proposal for specs that can exceed that objective by at least a factor of two on OM3 MMF.  This is a positive indication that the final spec will exceed the objective by wide margin.  In addition to the Flatman data you mention, both Steve Swanson and I have presented separate contributions supporting longer distance needs in data centers.   And, as we have heard during the discussions on 4km vs 10km SM reach objectives, connection insertion losses also need to be addressed beyond the 1.5 dB allocation of previous efforts due to both the increased use of structured cabling in data centers, which introduces central cross connection facilities, and the deployment of preterminated cabling that is favored for new installations in larger data centers, which doubles the number of connections per channel.

Under these considerations, specifications that support at least 200m on OM3 with at least 3dB of connection loss allocation would be optimal for data centers in my opinion.  

It is an established trend that high speed technologies are often first deployed in data centers then in LANs.  A 200m capability, while probably sufficient for DCs will not be optimal for LANs due to the greater geographical coverage of whole buildings compared to that of most DCs.  To aid eventual LAN deployment, the specifications should permit the support of the MMF solutions to at least 300m.  One means of enabling this distance lies in the specification of MMF more advanced than OM3.  John Dambrosia has recently announced receipt of the liaison letter on this subject from ISO/IEC that Alan Flatman and I noted in our separate contributions at the November 802.3 meeting.  This letter requests feedback  from 802.3 regarding the utility of the proposed specifications for a higher performance MMF.  Consideration for the future needs of in-building LANs would be a reason to encourage its standardization.

Paul Kolesar
CommScope Inc.
EnterpriseŽ Solutions
1300 East Lookout Drive
Richardson, TX 75082
Phone:  972.792.3155
Fax:      972.792.3111

Ali Ghiasi <aghiasi@BROADCOM.COM>

12/21/2007 12:54 PM
Please respond to
Ali Ghiasi <aghiasi@BROADCOM.COM>

[802.3BA] Reach Objective for MMF


On this reflector we have had many discussion on the SMF reach
objective.  But I want to bring
up your attention to the current MMF reach objective which is only 100 m.

High density data centers switches will be based on the QSFP (XFP width)
or the CSFP (~26 mm),
I do not see a viable serial 40G or 4x25G WDM solution in these form
factor in near future.
The current proposed 4x25G WDM will be housed in a double wide Xenpak
(~81 mm).

Currently for reach larger than 100 m you must switch to 100 Gig 4x25G
WDM!  Unless you are
designing your switch for reduce capacity double wide Xenpak will not
plug in to a QSFP or CSFP!
From pure density perspective you will be doing worse than dual stacked
According to Allan Flatman study page 7
300 m covers the building backbone and for larger data center more than
100 m may be needed.

In Atlanta I showed how even with sub 10G laser "300 m link on OM3 fiber
with linear receiver has 1 dBo less penalty than 100 m link OM3 with
limiting receiver"

I would like to explore the possibility of increasing the reach
objective on OM3 fiber from 100 m to
220 m or 300 m.  I do understand the draw back of ribbon cable, but here
we have situation where
the 4x25G solution just doesn't fit in to a QSFP/CSFP.  Maybe after a
season on biggest looser it might fit :-)

Happy Holiday,