Fiber Optic Networking Primer

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  • This Fiber Optic Networking Primer is a brief introduction to fiber optic networking. It should give you enough information to get past the worst part of the learning curve.

    Introduction

    Fiber optic networking sends data using pulses of light (usually in the infrared band that is not visible to humans). It begins at a transceiver which converts electrical signals into light pulses which travel through a fiber optic cable to another transceiver which converts the light pulses back into electrical signals.

    Compared to traditional copper ethernet, there are several advantages to fiber optics:
    • Not electrically conductive -- safer to run near high voltage power or between separate buildings.
    • Not susceptible to EM noise
    • Higher speeds possible
    • Extremely long ranges possible (10km+)
    Transceivers

    A transceiver is the thing you plug a fiber cable into. It is responsible for converting electrical signals into pulses of light, and vise-versa. Some transceivers will use two strands of fiber (one for transmitting, the other for receiving), while others require only one strand and use it for both sending and receiving.

    The most common type of transceivers you will encounter in 2021 are designed to fit into "SFP" and "SFP+" slots that are commonly found in network switches, routers, network interface cards (NICs), and fiber media converters.

    There are a number of compatibility concerns when dealing with transceivers of different models, so the easiest way to guarantee compatibility is to use the same model of transceiver at both ends of a fiber cable.

    Every transceiver is designed for a specific type of cable and connector (more on those later).

    SFP, SFP+, SFP28

    SFP slots can accept SFP transceivers for 1-gigabit speed.

    SFP+ slots can accept SFP+ transceivers for 10-gigabit speed, but are also backwards-compatible (can also accept regular SFP transceivers).

    SFP28 is the next step up from SFP+, supporting 25-gigabit speeds with SFP28 transceivers. It is also backwards compatible and can accept SFP+ and SFP transceivers.

    2 different cable types

    There are two commonly-used types of fiber optic cable, "Multi Mode" and "Single Mode". These are not compatible with each other, so for example you cannot use a Single Mode fiber cable with a transceiver designed for Multi Mode fiber.

    • Multi Mode
      • Uses thicker fibers.
      • Max range of 2000 meters (100 Mbps), 1000 meters (1 Gbps), 550 meters (10 Gbps).
      • 4 different commonly available cable grades: OM1, OM2, OM3, OM4. Higher number = better.

    • Single Mode
      • Uses thinner fibers.
      • Max range 10 km and beyond depending on transceiver power and cable quality.
      • 2 commonly available cable grades: OS1, OS2. Higher number = better.

    Most network links are short enough that you don't need to worry about range, and you can choose between multi mode and single mode based on pricing and availability of the cables and transceivers. If you need to install a fiber network link longer than you can find a prefabricated cable for, then I would recommend hiring a professional or exploring wireless networking options.

    Connector types

    There are many different connector types that can be used on the ends of the fiber. LC is one of the smallest and most common connector types, so it is well-suited for amateur installations.

    LC variants (LC-UPC and LC-APC)

    There are actually two variants of LC connector, and they are not compatible with each other, because of course it could not just be simple. The two variants are called LC-UPC and LC-APC. LC-UPC is by far the most common of these, to the extent that many products with LC connectors do not even specify which variant they use. LC-UPC male connectors are typically blue colored. LC-APC are usually green.

    LC duplex

    LC duplex connectors are just two regular LC connectors held together by a small piece of plastic which makes them easier to use with transceivers that require two LC connectors.

    Fiber Media Converters

    If you don't have a switch with an SFP or SFP+ port, you can use a fiber media converter to convert from fiber optic networking to traditional ethernet networking. A fiber media converter is just a box with one RJ45 ethernet port and one SFP or SFP+ slot. Often they come with a transceiver, but be careful to use them with a compatible fiber cable.

    The most basic fiber optic link would consist of two media converters (with transceivers) and one compatible fiber cable. This would give you a female RJ45 port on both ends of your fiber, ready to connect traditional ethernet cables.
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