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I'm about to buy cables for our first data center install. It's all Gigabit Ethernet. Should we use Cat5 or Cat6, UTP or STP?

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You want to use Category 6 or 6a (aka "Class Ea"), as this will allow use of 10 GigE over copper if you ever need it:

Cat6 allows for 37-55m (121-180 ft) cable runs (depending on how much electrical noise there is in the environment) for 10 GigE; Cat6A allows for 100m (330 ft) runs at 10 GigE. Either will be fine for 1 GigE. If your runs are with-in the shorter lengths, then Cat6 should be sufficient. Don't think UTP or STP would make much of a difference.

I'd get quotes for 'parts and labor' for each type of cabling and see what the cost differences are: it's usually easier to "future proof" things at the beginning than retrofitting things down the road.

If you're doing any fibre you may also want to look at the costs for both OM3 and OM4 (which was just released and will help with future 40 and 100 GigE support in your DC).

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For the UTP/STP part of the question - So UTP is the way to go? It seems much easier to get than STP, but I was hesitant because I kept reading differing opinions (STP 'mandatory' because of data center electrical noise etc.). – AX1 Dec 30 '10 at 19:43
cat5 or cat5e is not rated for gigE. STP is always going to be better imo. – Ablue Dec 31 '10 at 3:26
I'd say inside of a datacenter, fiber wouldn't make sense in a cost/benefit analysis. But I don't know the requirements so like DAM says get the quotes, with cabling it's ALWAYS better to future proof it on the front in, and way cheaper/esaier in the long run. – JamesBarnett Dec 31 '10 at 7:43

Unless you are severely cost constrained, CAT6 is the way to go. The future growth and similar cost to Cat5e makes it an easy choice. However, the additional cost of STP is probably not necessary unless your application has strict packet loss requirements or you are required by code to have shielded wire.

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CAT6A UTP is the most common copper in the DC. STP is only needed in cases of high EM noise if you have that high EM noise in your DC you have other problems. Bottom line is get your quotes and look at what you need and what your horizon technologies are.

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You could use unshielded CAT5 cable, but you really shouldn't. Especially in a data center, where there are lots of cables and quite some EM noise.

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cat5 or cat5e is not rated for gigE.

STP is always going to be better imo. less noise is better for SNR.

As a general guide, thicker wire (larger guage) is less resistant than thinner and current travels much better along it, so thicker wire is said to give you a lower signal attenuation (or loss), this is measured in db. Another helpful metric is the SNR (also measured in db) or signal to noise ratio. Noise is introduced to signal transmission it will effect how the signal is received. Shielding, and twisting pairs helps reduce noise.

Attenuation for a medium and SNR can be used with any signalling.

Most modems will provide this diagnostic, but for testing cables you will need expensive testing tools.

fiber optics barely attenuates at all. So the speeds attainable with that is much much higher than copper.

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