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I’d normally stuck to Copper Ethernet until fairly recently, but some work that I am doing now prevents me from using copper. I thought I’d put together a quick primer for people in a similar situation.

Unlike with ethernet-over-copper cables, inside fibre signals are transmitted via light instead of DC electrical current. Light rays are passed down incredibly thin glass cables. The glass cables are surrounded by cladding which ensures the entire ray of light is reflected back into the cable core (known as total internal reflection).

Fibre is traditionally available in ’single mode’ and ‘multi mode’. MM allows many light rays to pass through the fibre at once. The fibre strands are wider in MM fibre than in SM, so therefore the light reflects off the cladding lots. SM fibre is much thinner and therefore only a single ray of light can be passed down the strand. This leads to a number of behaviour characteristics:

• The lasers required to send light down the thinner SM fibres are more expensive, MM equipment is much cheaper.
• As the light bounces round in MM cable more often, it can only be used on smaller distances (typically 550m for 1000Base-SX MM fibre and 10km for 1000Base-LX SM fibre.)
• SM supprts Wavelength Division Multiplexing, or multiple channels of bandwidth along the same fibre. Several companies can share one physical fibre, and therefore the costs of a long fibre run, by buying a wavelength each.

The connectors at the end of the Fibres are small square connectors. SC and LC are typical presentations. SC is shown on the left of this photo.

When dealing with Fibre in Cisco, you tend to need to buy a Gigabit port and the GBIC which you plug the fibre cable into.