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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

There are so many types of cables and connectors it can be confusing when you are building a data centre. I’ve taken a look at the pros and cons of each so you can decide which is the best option for you.

The 10GbE standards were first published in 2002 by the IEEE and since then have been adopted gradually for use in data centres. Unlike the other Ethernet standards, 10GbE provides only full-duplex, point-to-point links usable for connecting network switches. Half duplex does not exist in the 10GbE world.

While 10GbE can use either copper or fibre cabling, the type of cable that you use is determined by your switch and what it can support. If your switch does not support 10GbE, then you cannot use 10GbE cables. It’s as simple as that.

What are your copper options?

10GbE: Can run on copper, also known as twisted-pair cabling or twin-ax cable, which costs less than fibre-optic cables. This is not the same 1000BASE-T cable that you would typically use to connect your laptop to the network, because not all copper is created equal. You need copper cabling that can handle higher bandwidth requirements – such as Cat6a or Cat7 – and it must be certified to at least 500MHz to ensure it can support 10GBASE-T.

Copper that is used for 10GbE can be passive or active copper: active copper cables use a chip within in the connectors to boost the signal and reduce the noise. Passive cables do not have this chip and have a direct connection between the cable ends. Think of active cables as passive cables on steroids.

With increasing interface speeds, active copper is being used more for its noise reduction and improvements in cable flexibility, such as distance and airflow.

10GBASE-CX4: Four lanes of 2.5Gbps combined together to form 1x 10GbE link, commonly known as InfiniBand. This presents a lower-cost and low-latency cable, but uses a much bigger form factor than the newer SFP+. If you have the SFP+ modules on your switches, you will need a converter to make 10GBASE-CX4 usable.

10GBASE-CR: Known as SFP+ Direct Attach, this is the most commonly used cable. It consists of twin-ax cable that connects directly into an SFP+ module. Similar to the 10GBASE-CX4, it is lower-cost and low-latency cabling, but has the advantage of being less bulky due to its smaller SFP+ form factor. 10GBASE-CR comes in varies lengths, ranging from 1m to 8.5m, with the most commonly used sizes being 3m and 5m. This makes the cable popular inside data centre racks.

10GBASE-T: Available as either unshielded or shielded twisted pair cables, in both Cat 6a or Cat 7 standards, with required 500MHz compliance. Cat 6 cables can be used up to 55 metres.

10GBASE-T has a slightly higher latency compared to the other 10GBASE-* cables due to the additional encoding overhead (forward error correction). The latency is in the range 2 to 4 microseconds compared to 1 to 12 microseconds on 1000BASE-T. This may seem insignificant to some, but when you are counting microseconds of a delay on an OLTP database, every pause counts.

Next page: Got Fibre?

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