I saw that computer Network Interface Cards (NICs) that use fiber ports (SFP) instead of RJ-45 ports and I wonder if there would be any significant advantage in connecting the computers directly through optic fibers instead of RJ-45 (UTP)

  • 2
    Don't forget disadvantages: larger bending radius, unsteadiness to fracture, larger cabling and port cost.
    – user36844
    Sep 6, 2017 at 6:23
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    Feb 19, 2018 at 18:44

4 Answers 4


There's several advantages to Fiber-to-the-desk

  • length: copper cabling is limited to 90 meters of horizontal cabling (leaving 10 meters for patching). Fiber doesn't have this limitation. In some building this can make a difference

  • cabled once for all: upgrading from 1Gbs to 10/50/100Gbs or a future Tbs doesn't require to recable the building, single-mode fiber will do the job (this is not true for multi-mode fiber). Considering the cost of cabling, this can be a huge advantage.

  • security: it's more difficult to spy (tape) on a fiber cable than on copper. By listening to the radio frequency, one can remotely listen the traffic that goes over a copper cable. I did a fiber-to-the-desk project in a diplomatic office and this was the reason to go fiber.

  • fiber is immune to radio interference.

  • 1
    Your second point is really only true if you run single mode fiber. Sep 15, 2017 at 17:19
  • One more advantage of fiberoptic - galvanic isolation. Oce I saw a spark discharge when connecting an RJ-45 connector to a PC. It's frightening and dangerous for equipment.
    – mmv-ru
    Nov 29, 2022 at 21:30

The main reason for fiber is reach: a fiber port with the appropriate optics can connect over many dozen kilometers - transceivers for 70 km or more are not uncommon. As of 2022, fiber Ethernet readily exists for up to 400 Gbit/s, with 800 and 1600 Gbit/s being developed. Other reasons include: electromagnetic immunity, thinner cable, harder to tap.

Copper is limited in reach (usually max. 100 m) and speed; the fastest copper Ethernet PHY, 40GBASE-T runs over just 30 m with special Cat.8 cable).

At the same time, fiber is more delicate and a lot less forgiving when it comes to day-to-day abuse: ignoring the minimum bend radius, pulling, kinking, bruising may very quickly damage a fiber patch permanently, often without visible damage. And they're somewhat more expensive.

SFP+/SFP28/QSFP+ NICs are very common in data centers for speeds beyond 1 Gbit/s. 10GBASE-SR uses a lot less power than 10GBASE-T and is about 1 μs faster due to less encoding overhead. Usually a data center provides a more controlled and protective environment than an office, so the fiber advantages very much outweigh the drawbacks.


There are some main advantages of using fiber optic cables instead of copper: Fiber optic transmission is faster; Fiber optic transmission results in less attenuation; Fiber optic cables are impervious to electromagnetic interference (EMI); Fiber optic cables do not break as easily. http://www.thefoa.org/tech/fo-or-cu.htm I hope this link may be helpful to you~


The obvious reason is you want more speed, and possibly also future proofing.

With gigabit Ethernet, within a few years of initial standardisation, the market had settled on basically the same standards used today. 1000BASE-SX for multimode fiber, 1000BASE-LX for single mode fiber and 1000BASE-T for copper. A few early adopters probablly got burned by deploying the dead-end standard 1000BASE-CX but said standard did not last long.

When we went up to 10 gigabit, there was initially no copper standard at all. Two years later 10GBASE-CX4 was introduced, but it required special cables and connectors borrowed from infiniband and had a range of only 15 meters. After another two years the IEEE standardised 10GBASE-T, this standard promised 10 gigabits over low cost twisted pair cabling, but it was plagued with high power consumption. Due to the power consumption it was initially only available as fixed ports, not as modular transceivers making it difficult to mix with other standards, so adoption was slow.

Instead the 10 Gigabit Ethernet world turned to a new concept for short runs, the "direct attach cable". These cables plug directly into the SFP+ transceiver slots on network equipment. Short direct attach cables are passive copper twinaxial cabling, while longer direct attach cables use fiber with permanently attached transcievers (which likely have lower optical specifications than standard transceivers). This concept has carried over to higher speeds.

Direct attach cables provide a cheap option for short runs, and since they were interchangeable with modular transceivers for fibre, flexibility was maintained. The idea of direct attach cables has carried over to higher speeds.

The downside of direct attach cables is that they need to run directly between the two pieces of equipment. They cannot run through patch panels or wall outlets. That is acceptable for equipment in the same rack and may be tolerable for servers in the next rack over, but it's not really acceptable for longer runs.

In recent years, 10GBASE-T has seen something of a renaissance. Improved electronics have reduced the power consumption issues, and it is now possible to buy 10GBASE-T SFP+ modules at a reasonable price, albeit they are still limited to 30 meters to reduce power consumption.

If you want speeds more than 10 gigabit, and distances more than "next rack over" then fiber is really your only option. 25GBASE-T and 40GBASE-T seem to be stillborn, they were standardised in 2016 but 6 years later it still seems utterly impossible to find any products for sale (or even products that have been announced but are not yet for sale). Searching the terms just finds articles about the standard and mislabelled direct attach products.

Finally, it's time to say something about single mode verses multimode fiber. Both types can typically support the latest speeds over short distances. However, for multimode the distances have been getting shorter, the grade of fiber required has been getting higher and/or the number of fibers required for a link has increased. So there is a very real chance that existing multimode fibers will not be suitable for a speed upgrade in the future. By contrast a single mode fiber pair installed in the 100 megabit era is likely still able to support the highest speeds today. The flipside though is that singlemode transcievers can be siginificantly more expensive than multimode ones.

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