Simple 2 Site / No Link

Unanswered Question
Sep 24th, 2009

I'm currently having an issue with a recently installed fiber run between two buildings. Here is the scenario.

Site 1 - Cisco Catalyst 2950, w/ GBIC module WS-G5484 1000Base-SX

Site 2 - Cisco Catalyst 3560 w/ SFP module GLC-SX-MM 1000Base-SX

Approx 1400ft of 50/125 OM2 multimode fiber has been run between the buildings. One termination done on each end - ST-SC on one side (GBIC) and ST-LC on the other (SFP). I'm currently getting no link status on both switches.

The cable installer is telling me everything has tested ok. He is pointing the finger at our Cisco gear. Before the switches were deployed I tested the switch hardware / modules in a lab using a patch cable and was able to establish a link just fine.

From what I was told, 50/125 OM2 fiber should be ok up to 500 meters @ 1GB speed. I'm not sure if this is a distance issue and that we should have gone with OM3 type fiber. Not sure where to go from here.

Please help - thanks!

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Tom Randstrom Thu, 09/24/2009 - 14:48

Does the cable installer have the tested losses for the two fibers running between the two buildings?

Are the jumpers being used multimode fiber (typically orange sheath)?

Are the connectors clean?

Do you have a power meter to check the received optical levels at each end?

tooslick1 Thu, 09/24/2009 - 14:56

The cable installer ran some tests and said there was minimal db loss. He either wasn't very specific or told me what the number was but because I'm unfamiliar with the tech I probably shrugged and don't recall what it was.

The jumpers are multimode using the same type 50 micron as the main fiber run.

The cable installer cleaned the connectors several times.

I don't personally have any equipment to perform my own testing. I am basically at the cable installers mercy at this point.

viyuan700 Thu, 09/24/2009 - 18:00

See the specs of your card at this link,

Ask your installer to use a Optical meter in front of you and see what is the value. if it is better than -17. As that is the lowest value it can go.

One more thing the distance for GLC-SX-MM 1000BaseSX is 550m or 1804 ft over OM2 fiber not OM3. Few things you can do ,Check your fiber manual and see what is MOdal Bandwidth for your fiber if it is 500MHz.Km then you fiber is fine. You should get 1804ft and as per ur message distance is 1400ft.

See this link

OM3 fiber has very high modal bandwidth value 2000 and it is for 10G kind of speed i dont see that at 1Gig they are talking about OM3 fiber.

Tom Randstrom Thu, 09/24/2009 - 18:16

A professional fiber optic cable installer should provide you test documentation on each fiber link that was installed. This would include the fiber link lengths and losses.

Another option is to borrow or purchase the LX/LH optics modules. This would give you an additional 150' of reach.

It is odd to not get any link. I would have suspected poor performance versus no link.

Are the fiber cables connected correctly, TX to Rx (I know, dumb question).

Are the modules seated in the switches?

If you connect a jumper from Tx to Rx on one GBIC or SFP, do you get link on that switch?

Are the interfaces active?

tooslick1 Fri, 09/25/2009 - 11:15

Per the installer:

The fiber loss before we cleaned it was .06 on blue

.02 on orange old building

.37 on blue with sigle and .21 on orange from new building

I'm positive the install was under 1400ft. The installer purchased a 1500ft spool and we have well over 100ft left, probably more. In all likelihood the run is more like 1350ft.

The installer brought the wrong patch cables so he cut the ends and re-terminated them with the correct plugs. Perhaps the patch cables are to blame.

The modules are seated correctly. Like I mentioned before, I pre-tested the equipment and was able to get a link using an SC-LC fiber patch cable.

Leo Laohoo Fri, 09/25/2009 - 18:13

You can test the GBIC by plugging both ends a simplex cable to both ports of the GBIC. Alternatively, you can plug one end of a duplex cable in to the port and plug the other end to the next one.

If the ports turn orange/amber to green then you've got a working GBIC. If not, then you should look at the GBIC.

tooslick1 Mon, 10/05/2009 - 13:29

It did indeed turn out to be a bad jumper/patch cable and is now resolved.

Thanks to everyone who helped.


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