Glass instead of copper. When you need it, which kind, and why the number written on the certificate is the whole point.

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When copper stops being the answer

Ethernet over copper is specified to 100 metres, and that 100 metres includes the patch cords at both ends. Past that the link is out of spec. It may appear to work, and it will be the thing everyone blames later.

Four situations where fibre is the right call:

• The run is longer than 100 m. The most common reason, and the least arguable.
• It goes between two buildings. Glass carries light, not current. Copper between separate buildings ties their electrical systems together and gives a surge somewhere to travel. This is the reason that matters most in a lightning-prone or industrial site.
• There is heavy electrical noise. Motors, drives, welding plant. Fibre is not affected by any of it.
• You want the run to outlive the gear. The glass in the ground will outlast several generations of switch. Pulling it once is the cheap decision.

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Singlemode or multimode

This is the decision that is expensive to get wrong, because it is decided when the cable is pulled and changed only by pulling a new one.

	Singlemode	Multimode
Core	About 9 microns. One path for the light.	50 microns on current grades. Many paths.
Distance	Far beyond any campus. Distance is rarely the limit.	Short. Tens to a few hundred metres depending on grade and speed.
Where it fits	Between buildings, along a property, anything long or permanent.	Inside one building, short runs, usually matching what is already installed.
The catch	Alignment is finer, so the splicing and the connectors have to be right.	Its distance ceiling arrives sooner than people expect at higher speeds.

AVNFi builds new outdoor and building to building runs in singlemode. If you are extending something that already exists, match what is there. A multimode patch cord on a singlemode link is a real fault that presents like a bad splice, and it has cost people a day of looking in the wrong place.

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How the joins are actually made

Fusion splicing

The two fibre ends are cleaved square, aligned, and melted together with an electric arc. The result is one continuous piece of glass with the lowest loss of any join, and it does not drift over time. It needs a fusion splicer and someone who can use it. This is what AVNFi does.

Mechanical splice

The two ends are aligned inside a sleeve and clamped, with a gel between them to help the light across the gap. It is quick and it needs no splicer. It also has higher loss than a fusion splice, and it ages. It has a place as a temporary measure to get a building running tonight. It is not a permanent repair, and it should not be sold as one.

Pre-terminated assemblies

Factory made, connectors already fitted, tested before it ships. Excellent where the length is known in advance and the route allows the connectors to be pulled through. No good when the run has to be cut to fit on site.

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Testing, and what each test actually proves

Two different instruments answer two different questions. People conflate them constantly.

Instrument	The question it answers	What it cannot tell you
Light source and power meter	Does this link work, and by how much margin? It measures the actual light lost end to end, which is the number the equipment cares about.	Where a problem is. It gives you one figure for the whole link.
OTDR	Where is the event? It sends a pulse and reports reflections and losses with a distance to each, so a break becomes one hole in one place instead of a trench.	The true end to end loss. It infers rather than measures it, and it is not a substitute for the meter.

A finished job should come with the measured loss for each link, written down. Not a promise that it passed. The number, so that in three years someone can measure it again and see whether anything has changed.

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Where fibre meets a UniFi system

Fibre does not plug into an RJ45 port. It goes into an SFP or SFP+ cage, which takes a small module, and that module has to match the fibre: a singlemode module on singlemode glass, multimode on multimode, and both ends the same.

• Cloud Gateway Fiber (UCG-Fiber), $431 all-in. The console built around a fibre input, for a fibre service coming into the building.
• Inside a rack, do not use fibre at all. A direct attach cable is cheaper and there is nothing to clean or break. The 0.5 m 10G cable (UACC-DAC-SFP10-0.5M) is $19 all-in.
• Port counts and speeds for every console and switch are in Gateways and Switches.

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What goes wrong

• A clamped joint sold as a repair. It gets the building running. It is not the finished job, and the loss creeps.
• Water in an enclosure. A splice case that fills over a winter loses a little more each month until the link drops. It usually fails on a cold night.
• Nobody measured it. Without a first reading there is nothing to compare against, so a link that is slowly degrading looks fine until it is not.
• Bend radius. Fibre pulled around a tight corner or cable tied hard loses light immediately and can crack later. The damage is done at install and shows up months on.
• Dirty connector ends. A fingerprint on a ferrule is a real fault. Ends get cleaned and inspected, every time, before they are mated.
• Assuming it is the carrier. Sometimes it is. A trace and a loss reading turn that argument into evidence.

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Related

• Bridging and Connectivity, for when a trench is not possible and the link has to go through the air.
• Switches and PoE, for the ports the fibre lands on.
• Choosing a Gateway, including the fibre console.
• Glossary.

Fibre is its own trade and it does not depend on any one manufacturer. AVNFi builds fibre for new construction and retrofits, and splices, locates and certifies existing runs, in Calgary and across Alberta. See fibre installation and builds or splicing, OTDR and loss testing.