10 Gig distance and Modal Bandwidth on MMF

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Jun 22nd, 2010
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I am struggling with a concept and not finding much in the way of answers.  The spec sheets for SFP+ 10 Gigbit Ethernet optics list the maximum cable distance as a funtion of the fiber type (MMF or SMF), Optical Wavelength, Core diameter and Modal Bandwidth.  However, there are several distance entries for similar items that only differ in their modal bandwidth.


For example a SFP-10G-SR when connected to 62.5 micron MMF lists the maximum cable distance as either 26M or 33M depending on the modal bandwidth (either 160 or 200).  Is there a way to figure out what the modal bandwidth of a given fiber strand is (short of performing a full fiber characterization study)?  It seems that there is no relationship between the grade of MMF (OM1, 2, or 3) since 62.5 micron fiber should all be considered OM1.


This is becoming an issue since many companies are wanting to run 10Gigabit Ethernet over some incredibly old fiber plants, and I am trying to get an handle on which distance measures listed in the spec sheets are more realistic when they list multiple distances for the same fiber type that only differ in modal bandwidth.

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Tom Randstrom Tue, 06/22/2010 - 17:49
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Based upon my readings, testing a fiber for modal bandwidth is not something that is done within the field but during production.  Thus, you would need to have the specification sheets for the installed fibers (you can stop laughing now).  However, from what I have read, older fibers may not have been characterized or they didn't publish the modal bandwidth because they were not critical at the networking speeds being used. 


The attached paper, which you may have already read, was interesting.  You may want to contact a fiber applications engineer at Corning and see what information you can pull from them. 


The industry is always trying to extend the life of the installed medium or improve the performance of newer generations.  Unfortunately, this can cause ambiguity as we move forward in time. 


Tom

viyuan700 Wed, 06/23/2010 - 11:20
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"10Gigabit Ethernet over some incredibly old fiber plants, and I am trying to get an handle on which distance measures listed in the spec sheets are more realistic when they list multiple distances for the same fiber type that only differ in modal bandwidth"


If you dont have fiber spec given by the manufacturer and fiber is quite old then make sense to go with lesser distance within the same fiber type. Like 26m for SFP-10G-SR.

paulblakie Wed, 06/23/2010 - 11:24
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@ viyuan700 - unfortunately moving the buildings closer together isn't an option.


Paul Blakie

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viyuan700 Wed, 06/23/2010 - 11:36
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"moving the buildings closer together isn't an option"

using a long haul optics will be cheaper than moving the building

Tom Randstrom Wed, 06/23/2010 - 12:33
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"unfortunately moving the buildings closer together isn't an option"


Everything comes down to money.  If they want to use the older fiber, show them a cost comparison between the cost of moving the building versus installing long reach optics (10G LRM or LX4), pulling new fiber or installing a 10GE Free Space Optics link between the buildings. Just wait until the customer wants to move to 100GE links over the fiber....


For some fiber links, you may have to test by installing some 10G equipment.  I have not found information regarding how long the OM1 (with low modal bandwidth) was manufactured.  Fiber can be highly variable and sometimes the distance specs leave some operating margin and may support the longer link.


Good luck!


Tom

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