The internet IS a series of tubes. Kinda: A Reg 101 guide to cabling

Pick a copper-bred road or carry on up the fibre

Got Fibre?

Let’s break down the different types of fibre-optic cables. In common with copper, not all fibre-optics are created equal. There are differences in their distances and indoor/outdoor use ratings, and there are consequently two main types of fibre-optic: Multi-Mode Fibre – MMF (OM1, OM2, OM3, OM4) – and Single-Mode Fibre, or SMF (OS1).

The difference between SMF and MMF is that with SMF, the light follows a single path through the fibre, while MMF uses multiple paths. The SMF has a narrow core of 8.3µm compared to MMF's 50 or 62.5 µm. SMF requires more precise termination and connection. Both SMF and MMF come in two wavelengths, 850nm and 1300nm, with the latter supporting longer distances. Typically SMF cables are yellow, MMF cables are orange, and OM1, OM2, OM3 and OM4 are aqua. OM4 is also coloured violet by some vendors.

MMF fibre is easier to install and costs less than SMF, but MMF is used for short distances of less than 300m, compared with SMF, which can be used for distances of up to 6.4 miles (10km). That distance is the standard maximum, however distances greater than 80km are possible if all the right pieces – the transceivers and the buffers – are perfectly aligned.

New cabling of both types now has enhanced bending sensitivity, allowing for greater use in tight bends with minimal signal loss.

10GBASE-SR: The most commonly used fibre-optic cabling for 10GbE is the 10GBASE-SR cable. The 10GBASE-SR is a MMF, short-reach cable that supports an SFP+ connector with an optical transceiver. Due to its lower cost and lowest power, 10GBASE-SR is a popular fibre-optic choice. The OM3 and OM4 are both laser-optimized MMF fiber that were designed for faster networks such as the 40G/100G Ethernet standard that was published by IEEE in 2010.

10GBASE-LR: These are long-reach fibre-optic cables that support single-mode fibre and connectors. They are intended to be used over long distances, such as connecting data centre to data centre. However given that cost of OS1 fibre has come down in recent years, SMF is used as the fibre of choice for runs between floors of building.

10GBASE-LRM, 10GBASE-ER, 10GBASE-ZR: These are other long-reach and extended-reach fiber, and are not discussed here because they are not “common” types.

A connection is made

Now you’ve got your cables, what about your connectors? There are several types of connectors available for 10GbE cables, all with varying degrees of supported lanes and speeds. The most widely used connector is the SFP+. If you want higher speeds you would bond multiple lanes, for instance bonding 4 of the 10GbE lanes to give you 40Gbps.

Or, to put all that another way:

	Type	Lanes	Max speed per lane (Gbps)	Max speed total (Gbps)	Cable type	Usage
Copper CX4	CX4	4	5	20	Copper	10GbE (max 10Gbps), SDR and DDR InfiniBand
Small form factor pluggable	SFP	1	4	4	Copper optical	10GbE, fibre channel, 1,2,4Gb
Small form factor pluggable enhanced	SFP+	1	16	16	Copper optical	10GbE, 8Gb and 16Gb fibre channel, 10GB FCoE
Quad small form factor pluggable	QSFP	4	5	20	Copper optical	Various
Quad small form factor pluggable enhanced	QSFP+	4	16	64	Copper optical	40GbE, DDR, QDR and FDR, InfiniBand, 64Gb fibre channel

So, which cable is the right cable? It depends on your environment, on the switch equipment you have and on what price and quality you want, if your current equipment does not suit your needs.

When the requirement is for short runs – inside a rack, for example – 10GBASE-CR would be the best bang for your buck. You get the performance you want without paying the costs of fibre. If you need to get 10GbE in longer distances, but not quite in the miles range, using MMF cables such as OM3 or OM4 with SFP+ connectors would be a good option.

For anything that is beyond your data centre, the 10GBASE-LR or the other long-reach fibre should be used. However, if you are running fibre between floors of your building, the 10GBASE-LR can also be used. While most deployments of 10GbE use SFP+, you can still use 10GBASE-T if your switch and network adapters support it. ®