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Minimum distance for GBIC-ZX

What is minimal distance for connection two GBIC-ZX. Could I connect they on distance less then 10 km - for example 1 km with 10 dB or 15 dB attenuator put on receiving site ? What it depend on ?

Thanks for any suggestions !!!


Community Member

Re: Minimum distance for GBIC-ZX

Hi Maciej,

The minimum cabling distance for the ZX GBIC is 6.2 miles (10 km) with 8-dB attentuators installed at both ends of the link and 24.9 miles (40 km) without attenuators.

For details on GBIC Port Cabling Specifications refer:

Community Member

Re: Minimum distance for GBIC-ZX

Thanks for information, but do You know why I can't use GBIC-ZX for distance less then 10 km with attenuator for example 10 dB or 15 dB. It is possible ?

What is limitation ?


Community Member

Re: Minimum distance for GBIC-ZX


I can't see why there won't be a problem as long as you attenuate the signal enough so the rx is not over loaded. 10dB or 15dB should be fine.



Community Member

Re: Minimum distance for GBIC-ZX

The problem with using them for such a short distance is not a technical problem. These devices can cost up to $3000/gbic while the Gbic that handles 10km is around $300. You wouldn't use a Ferrari to haul horse manure.


Re: Minimum distance for GBIC-ZX


If you put 10dB or 15dB in-line attenuators in the Rx ports of the WS-G5487 1000BASE-ZX GBIC, and you use a single-mode fiber patch cable at least 2 meters in length, you will be fine. This is often done in a lab setup, or to test a configuration prior to installing systems kilometers and kilometers apart.

Previous post by RBergman is correct in pointing out that for an installation under 10km, it is hard to cost-justify installing ZX GBICs where LX/LH GBICs will get the job done for less than 15% of the price. However, there are circumstances where the ZX may be the solution in a run under 10km. For example, if you have to use a single-mode fiber span with end-to-end measurable loss greater than the loss budget of the LX/LH, but less than the loss budget of the ZX (9.5dB or 10.5dB for the LX/LH, vs. 23dB or 24dB for the ZX, depending on which Cisco specs you read). I had a situation once where it was less expensive and quicker to get a customer up and running using a pair of ZX GBICs than it would have been to reinstall several km of new single mode fiber. Besides the larger loss budget we got, we also lost less in per-kilometer attenuation at the 1550nm vs. 1300nm wavelengths.

In any short-distance situation with ZX GBICs, the key is to PROTECT THE RECEIVE OPTICS. Cisco specifications say the ZX's maximum Tx optical power is +4.77dBm, +5dBm, or +5.2dBm, depending on what you read. The maximum Rx is -3dBm or 0dBm, again depending on what you read. So, using the worst-case extremes, +5.2dBm transmitted directly into a receive optic capable of at most -3dBm results in an overdrive of 8.2dB. If you protect the Rx optics by giving them 9dB or greater "sunglasses", then as long as you don't overattenuate the signal to the point of exceeding the loss budget, you are guaranteed to work.

Hope this helps.

Community Member

Re: Minimum distance for GBIC-ZX


on the same subject, i have the following problem. i tried exactly what you suggested, using patch chords and a 10db attenuator between 2 zx sfps. link didn't come up.

i borrowed a couple of lx sfp and tried them with the same single mode patch cords, the link didn't come up again.

now, i borrowed a small fiber loop from cisco. and not only did the lx sfp come up, but the zx did too.

fibers are new. they are single mode fibers. we tried 4 separate NEW singlemode fibers.

what could be wrong?

(i'd appreciate it if we could talk about this off line)




Re: Minimum distance for GBIC-ZX

It sounds like the two strands in your patch cords aren't crossing over between the SFPs.

Trace the two strands on your patch: make sure the one plugged into the TX port of the first SFP goes to the RX port of the second SFP; and the other, plugged into the RX port of the first SFP, goes to the TX port of the second SFP, like this:



It could also be bad patch cables, since you know the LX/LH and ZX SFPs worked with the fiber loop from Cisco. What kind of single mode fiber patch cables are you using?

Community Member

Re: Minimum distance for GBIC-ZX

Minimum distance for GBIC-ZX is 34 cm (30 cm patch-cord + 15 dB attenuator), unless you find a shorter cable

To make it work just use SM fibers and keep the receive power level within GBIC' specs.

1000BASE-ZX Specs:

   Transmit Power (dBm) = +5 to 0

   Receive Power Range (dBm) = -3 to -23

In our labs we always use 1..2 m cables with attenuators to run tests and static setups.

NOTE: Generally it is recommended to avoid using hight power GBICs for very short distances, as some amount of energy could be reflected back into the transmitter, which can damage it over long time.



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