I'm new to Ethernet over Fiber, so please bear with me.

According to the standard, 100BASE-FX over SMF supports distances up to 10 Km. Technical documentation of some products states support for 100BASE-FX with typical distances of up to 40 Km. Some even go as far as supporting up to 75 Km.

  • Isn't that against the standard?
  • Would a repeater allow reaching longer distances, e.g. 100km?
  • What happens if you use single-mode fiber for shorter distances, for instance < 1 Km?

NOTE: If you are going to downvote me, at least leave a comment, so I'd know how to post next time.

  • Distances are not in the standard is laser power and fiber mode . Mono mode = longer distance in hard fiber and multi are for cheaper fiber and flexible one. – YuKYuK Feb 16 '15 at 15:28
  • Yup it depends on the media converter / fiber module specs and the fiber type – Dan Feb 16 '15 at 15:50
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    @Dan The issue is, if I google something about this subject, I just get bombarded by products. Although I'm just looking for information – H_squared Feb 16 '15 at 15:54
  • What I remember is having several types of media converters on the shelf, one pair was long distance, one not, they had written on them the maximum distance. Sorry not specialized in fiber optics. Usually media converters (or optical modules for switches/routers) come in pairs, esp. single fiber types (in which case one is type "A" and one is type "B" because they use different wavelengths for rx and tx) – Dan Feb 16 '15 at 15:59
  • I thought 100base-fx was MM-only and went 2km. Regardless, it's an ethernet standard, which means it's just a way to encode data in a waveform. So technically a product vendor could try to push that signal out as far as they want, regardless of what the standard recommends. – jlehtinen Feb 16 '15 at 22:11

Aside from 100BaseFX being very obsolete in this day and age, the main constraint on distance with single-mode fiber is power input (.vs. fiber attenuation/loss) and receive sensitivity. But seriously, replace with 1000BaseLX when convenient and reap the rewards of 10 times more speed on the same fiber for potentially as little as $10 (used gigabit SFPs are quite inexpensive.) 10Gig will run on the same single-mode fiber but it will cost a lot more than 1 gig.

10 km single-mode is pretty simple and foolproof for moderate values of fool. If you plug two SFPs together with a 5 m patchcord, they work. If you plug them with a 10 km fiber in good shape, they work.

Longer distances can get difficult in the hands of moderate fools, as the power output by the laser may exceed the receiver's input capacity, unless it has been attenuated (by a long fiber, or by a fiber attenuator) So it becomes possible to burn the receiver if short cords are used without attenuators, say while "testing." Check the data sheets for the particular SFPs to see if this is a potential problem.

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