If we purchase a single strand of dark fiber which spans 120km, is it possible to light it at 10Gig?

We will be using a 6509 switch at one end and a 4948-10GigE at the other end.

We have not purchased the optics yet, nor the line card for the 6509. We are looking at the ES/ES+ linecards

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    Commented Jan 3, 2021 at 6:11

3 Answers 3


The distance of the fibre isn't a good indication of whether you'll be able to run a specific optic/speed across it.

You need the path loss (measured in dB), which can vary greatly between links of the same distance (due to number of splices, fibre quality etc.) Also, the distance of the fibre in the ground is usually about 25-30% longer than the path it travels to allow slack for re-splicing, so you'll really need this info up front.

I'm not sure that that sort of distance will be possible at 10G with any off-the-shelf optics regardless, without some amplification. There are however 1GE SFPs that should be able do this (-28dBm RX sensitivity)

  • 2
    And people say RFC1149 doesn't have practical usefulness. tools.ietf.org/html/rfc1149 Commented May 29, 2013 at 5:28
  • We are getting some stats from the supplier. Are there SFPs available that will do 10Gig over that sort of distance with a standard pair?
    – rick
    Commented May 30, 2013 at 21:20
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    Not that I have seen - most long-range optics for 10G will be XFP rather than SFP+ due the lower power available for the module allowed by the SFP+ spec. That said, long-range optics are usually characterised by their receiver sensitivity (how well they can re-construct a bitstream from a low signal), rather than their ability to blast more light out. Commented May 30, 2013 at 21:56

as @dfex said you really need to measure the true attenuation before proceeding. There are special transceivers that have FEC and claim to achieve extended reach (for example from Menara Networks). However I would probably go with traditional amplification and with some small DWDM system.

  • 1
    Or just buy a wavelength or two Commented May 29, 2013 at 5:36
  • Do you mind elaborating on that? Perhaps post a link to some details about traditional amplification.
    – rick
    Commented May 29, 2013 at 22:16
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    I believe the most common way is the EDFA. You can get amplifiers as standalone or part of a DWDM system. There are many vendors to choose from and prices can vary quite a lot. There is a nice principal drawing on MRV's homepage.
    – aakso
    Commented May 30, 2013 at 6:08

Not with a 4948-10GE I'm afraid. X2 transceivers can only go up to 10GB-ZR which will get you ~80km.

Edit: dfex is right on the money as well - you'll need to get the path loss from your provider before you can make an informed decision on this.

2nd edit/suggestion - if the path loss still prohibits you from off-the-shelf optics, maybe ask your provider if they can give you a wavelength instead, at least until you decide if *WDM is a more viable option for your needs.

  • What about with the Cisco OneX Converter Module?
    – rick
    Commented May 29, 2013 at 5:08
  • 1
    Just changes the form factor into something smaller unfortunately - AFAIK there aren't any SFP+ optics that you'll be able to get that kind of range with. Commented May 29, 2013 at 5:15

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