SFP/mode conditioning

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Aug 5th, 2010
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I have some Catalyst 3560 switches that I need to connect over a long distance. The existing backbone is 62.5 850nm multimode and unfortunately I dont have the option of installing single mode fiber at this point. The distances range from 2000' to 6000'.

My question is - is this possible? and what parts would I need to make this work at 1GB/s?

I'm looking into the possibility of using a mode conditioning cable on both ends and a single mode SFP adapter for the switches. However, all I can find on the mode conditioning cables reference 1300nm and our existing fiber is 850nm. Is this a limitation of the existing fiber? Are there mode conditioning cables that support 850nm or does the SFP dictate what wavelength we are using?

Thanks in advance!

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jdeland80 Thu, 08/05/2010 - 13:49
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Thank you for the reply. I'm with you, I thought the GLC-LH-SM was the answer as well. My main concern was that under its description is mentions 1300nm and I've been told the existing fiber backbone is 850nm. Should this be a concern?

I've also been told that I can't use a single mode SFP over a MM fiber - but I thought thats what the mode conditioning cables were all about. Any ideas on that?

Thanks alot for your time it is very much appreciated!

Tom Randstrom Thu, 08/05/2010 - 14:12
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I saw that my original post had an incorrect URL for the 2km MMF document (which I corrected within my original post).

There are plenty of caveats outlined in Cisco's document for the operation up to 2km over MMF.  Alot really depends on how old the fiber is and its modal bandwidth.  You cannot test for modal bandwidht in the field, so Cisco has you test the link for bit errors.  You must use a Mode Conditioning Patchcord, which takes the laser light and launches the light stream into the sweetspot of the MMF.  The 1310nm wavelength has lower loss within the fiber so the light will travel further in the fiber. However, dispersion is what will limit the distance of this link.

Fiber Basics



Tom Randstrom Thu, 08/05/2010 - 12:50
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Take a look at the following Cisco document on operating 1GE over 62.5um MMF up to 2km....

Cisco Support for Gigabit Ethernet Deployments  with Multimode Fiber Links up to 2 km


Depending upon your equipment, the GLC-LH-SM will probably be the SFP for your equipment.  You can look at the following compatibility document...

Cisco Gigabit Ethernet Transceiver Modules  Compatibility Matrix


I hope this helps.



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