GBIC/SFP Not Linking

Unanswered Question
Jul 12th, 2010

I'm rather unexperienced in the optical networking, so I'm looking for some advice.

I manage one end of a fiber link to our internet provider, on my end I have this switch:

cisco WS-C2950G-48-EI


It has a GBIC labeled 30-0703-01 1000Base - LX 1300nm Laser

From the GBIC there is a cable with the same style connectors on both ends that goes to a fiber patch panel, then on to my provider.

The patch cable is 2 strands bonded together that are yellow, with blue ends, and has printed on it the text Optical Cable Corporation .... Single Mode .... Riser

I'd like to replace it with this switch:



This switch has a SFP labeled GLC-LH-SM 30-1299-02

And I have a patch cable that is orange with tan connectors (black boots) on both ends, one end of this cable fits the old GBIC/Patch Panel, the other, the new SFP. (it was sold to me as N316-01M Duples Fiber Optic Patch Cable - 1M LC/SC 62.5/125 Fibre) The packing slip says "FPC MM 62 2F LC SC 1M" "CERAMIC OFNP ZIP (2.0MM) CRN"

When I plug the new SFP into the patch panel with the orange cable, I don't get any link lights on the SFP, when I link the two switches together with the new cable, I get a link.

What can I do to diagnose this problem, and make this work?

I have this problem too.
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Tom Randstrom Mon, 07/12/2010 - 09:51

You should use a Singlemode Fiber (SMF) patch cord to connect the GLC-LH-SM SFP to you patch panel.  You need to order it with an LC-type connector on one end and a SC-type connector on the other.

The orange patchcable you are trying to use is for Multimode Fiber (MMF). You get a link light when you connect the two switches together because the fiber patch cord is short enough for the signal to be received without being too distorted.  But, your fiber link to your service provider is longer and when you connect a MMF cable to a patch panel with SMF fiber, you will lose some additional light. 

Do you know the distance between your service providers equipment and the patch panel?  Do you know what type of fiber is connected to the back side of the patch panel?  I would assume it is SMF because that is the type of patch cord the GBIC was connected with (and was previously operational).

Let me know if you have any additional questions.


sescjgalvez Mon, 07/12/2010 - 10:35


Thank you for the clear answer, I guessed that may be the case.

I don't know what is on the back side of the patch panel.  It's hard for me to see.

It's about 1.5 miles to my providers premises.

Tom Randstrom Mon, 07/12/2010 - 12:10

At 1.5 miles, it is definitely singlemode fiber in your patch panel and outside plant cable to connect to the service provider. Best not to go poking around behind your patch panel.  It is typically very crampedand dark and the fibers connecting to the back connectors typically are not as well protected as a standard jumper cable.

A simple fiber jumper should get the network operating again with the new switch.

Good luck.

viyuan700 Mon, 07/12/2010 - 10:42

What can I do to diagnose this problem, and make this work?

As Tom mentioned you need a Single Mode Fiber Patch Cable instead of N316-01M Duples Fiber Optic Patch Cable - 1M LC/SC 62.5/125 Fibre) The packing slip says "FPC MM 62 2F LC SC 1M" "CERAMIC OFNP ZIP (2.0MM) CRN".

As far as i know a receiver interface have lens which is bigger than the Core diameter of Single mode fiber (8-10micron) so you get the link but it is possible that when you try you get errors (You can try by connecting your 2 switches with you Multimode Cable and test with some traffice.)

But when you are trying to connect to a patch panel which is single mode, you are trying to send light from a 62 micron pipe to a 9 micron pipe which is very difficult.So you have no link.

If you want to try , A simple experiment will tell you how easy is to couple ligh into a Multimode cable, Just keep a MM patch cable in front of a light bulb and you can see light other end . Try same thing with Single mode cable you will see nothing.


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