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I am new to networking, know about Ethernet and that Ethernet cables exist to make a wired networks. I also know about fiber optic cables which have a glass like material inside and transmit light signals instead of electrical ones. Now my question is, can I use fiber optic cables to for Ethernet or different type of implementation is made using fiber optic cables?

Thanks for your time!

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    Again, homework?
    – cpt_fink
    Commented Aug 5, 2018 at 4:36
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    "Ethernet and that Ethernet cables" You need to specify the type of ethernet cable. Ethernet runs on a variety of media: coax, UTP, STP, fiber, free-space laser, etc. Many people call UTP cables ethernet cables, but UTP can be used for other protocols, e.g. token ring, T1, POTS, etc. When you say ethernet cable, you must be specific to the particular medium you mean.
    – Ron Maupin
    Commented Aug 6, 2018 at 22:11

3 Answers 3

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Ethernet uses a variety of cable types - an Ethernet cable can be pretty much anything. Ethernet has been using optical fiber for decades. The first standard was 10 Mbit/s FOIRL in 1987, the currently fastest fiber PHYs run 400 Gbit/s. 800 Gbit/s and 1.6 Tbit/s started development in 2021. Fiber is actually the cable type with the most Ethernet variants by far, more than all others combined.

Fiber has become common in datacenters due to the bandwidth and reach limitations of twisted-pair copper - currently and probably permanently limited to 40 Gbit/s over only 30 m of category-8 twisted pair or just 10 Gbit/s over the full 100 m (of category 6A).

Depending on your requirements, you're probably looking for one of these:

  • 1000BASE-SX: 1 Gbit/s over up to 550 m of OM2 multi-mode fiber
  • 1000BASE-LX: 1 Gbit/s over up to 10 km of OS1 single-mode fiber
  • 10GBASE-SR: 10 Gbit/s over up to 400 m of OM4 MMF
  • 10GBASE-LR: 10 Gbit/s over up to 10 km of OS2 SMF

(minimum fiber grades for full reach)

There are many other fiber standards for various data rates and distances, also many common vendor-specific or MSA ones for even longer distance. The required optical transceivers are usually SFP (1G) or SFP+ modules (10G) plugged into your network hardware. External media converters for devices without SFP slot are also available.

For a complete, up-to-date list of physical layer variants you can check Wikipedia: Ethernet physical layer.

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Now my question is, can I use fiber optic cables to for Ethernet or different type of implementation is made using fiber optic cables?

Ethernet can be thought of as having multiple layers, exactly how many depends on who you ask and which variant of Ethernet you are talking about but we can divide it into four main parts.

  • Framing/filtering, encapsulating the higher level packets into an Ethernet frame with source and destination mac address and filtering packets based on those MAC addreses.
  • Serialisation and where nessacery medium access control, taking packets in memory and turning them into line-rate streams of data sent at the correct time.
  • Physical layer encoding, turning line rate data streams into electrical or optical signals suitable for the physical medium.
  • Physical medium, the actual wires or glass that carry the data.

The key is that as long as the first of these stays the same we can build a single consistent network, the end devices only need to know about the lower ones for their immediate link, they don't have to care about what they are on the rest of the network.

In some cases, external or pluggable transcievers are used, so the end device doesn't have to care about the last two points even for it's immediate connection. Those details are encapsulated in the transciever.

So yes the implementation details are different between Ethernet over Twisted pair and Ethernet over Fiber (and there are multiple variants of each) but it is still considered Ethernet.

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This Wikipedia page has a summary of all Ethernet physical layers: Ethernet physical layer which may be of interest. It lists all optical physical implementations mentioned by https://networkengineering.stackexchange.com/a/52290/19509 and more. There is also this other Wiki page stub for Ethernet over fiber.

One interesting point that we can see from the tables is that starting from 50 Gbit/s, only optical fiber and twinaxial implementations exist. Twisted-pair cables currently stop at 40 Gbit/s and only with Category 8 cable in 40GBASE-T, with the ubiquitous Cat 5e cables only going up to 2.5 Gbit/s in 2.5GBASE-T. I.e., "optic cables are faster than twisted pair".

Another important dimension besides bandwidth is the maximum cable length allowed. In this aspect, fiber optics also achieves much higher values, I can see up to 100 km for 1000BASE-ZX fiber, while for twisted pair I don't see anything beyon 100 m, reached e.g. by 2.5GBASE-T.

Perhaps a more dramatic illustration of the existence of ethernet of fiber is to just look at a switch model that has both fiber and twisted pair enter image description here

and on the image we can clearly see that there are two twisted pair ports (TP1, TP2) and two SFP ports for fiber (SFP1, SFP2), so we can imagine that this switch transparently handles Ethernet between either twisted pair and fiber optics.

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  • @Zac67 I would recommend allowing people to at least mention the existence of concrete product examples, as that makes things more clear and vivid for readers. I'm not recommending them in any way, and am not affiliated with them in any way nor have I ever used them. Commented Jun 26 at 16:54
  • The photo is quite sufficient for the purpose, no need to 'mention' anything that the OP hasn't. It's better this way, believe me.
    – Zac67
    Commented Jun 26 at 16:56

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