most common twisted pair cables

Doug Davis wrote in part:

Oh, dear me. Learn to Google and use the wiki unless you want to be embarrassed by your students.

The choice is between Cat5e and Cat6. Occasionally people find and run lower for residential POTS.

-- Robert

Teach them facts. The bulk of cabling costs is labour. Not wire.

Therefore: if you lay new cables, uses the latest / fastest type of cable available. And lay at least twice the amout of cable, you forsee to use :-)

And if you want to give them an edge: tell them to put an extra pull-wire in as well.

...and a couple of fibres too when you're at it.

New installs should be cat 6

Not necessarily. Cat6 is more difficult to get right than Cat5, it is more expensive to certify and Cat6 cable[1] is considerably more stiff and has a greater diameter than its Cat5 equivalent.

So there still are arguments for a Cat5 installation, the main one being that just using Cat6 cable and Cat6 termination equipment will get you nothing more but an expensive Cat5 link most of the time, except when you are adequately trained, have the equipment to certify the link and have enough knowledge how to fix common problems.

Given that CAT5e can do GBe if properly done, what is the case for CAT6, anyway?

It's more expensive and thus makes a bigger profit for the people installing it? :-)

OTOH, for shorter runs it supposedly will be able to support 10GBase-T (802.3an-2006, 10 Gb Ethernet over copper/RJ-45), various sources says

Cat6A and Cat7 installations can handle 10GBase-T for the full length (100m), but as usual you have to weight in price and other factors.

But even when Cat5E is significantly cheaper it may make sense putting in a couple of Cat6A/7 runs when doing a big bundle, the same way that it's not uncommon to put in a couple of fibers too at the same time (though I suspect there's a number of people who are surprised how short the max distance for 10GBase-SR over legacy multimode fiber can be).

Aside from this obvious and important advantage, Cat6 will also support other balanced high-frequency signals much better than Cat5 - balanced RF over a short distance being one example. Due to the S/STP shielding common in Cat6 but rather uncommon in Cat5, it is better suitable for cable sharing applications or applications are sensible to EM irradiation.

However, GBe will be a sufficient to-the-desk data rate for the next years and other non-ethernet applications apparently are going to vanish over time - media servers and streaming clients might replace typical TV cable installations, VoIP might replace POTS, IP cameras are about to replace CCTV installations. So doing new Cat5e installations is not wrong - in 10 years we might want to replace the cable with something completely different (like fibre) anyway.

We should go fibre too already now IMHO. Modern edge devices already support it. See

Fibre is not versatile enough. Even with the amount of used analog signals decreasing (you will not get POTS or ISDN through fibre, you will have to pay a lot of bucks to have KVM extenders run over fibre) you still have the problem of power - PoE comes naturally with copper, with fibre you would need to run a conducting pair with it. And who wants to sacrifice the new feature we all learned to value with small PoE powered switches, access points and VoIP phones for some fibres of crystal? At least not just for the look of it.

The short answer to your question is: CAT5E is most common Longer version: CAT5E is most common because it is (relatively) cheap and supports 95% of the application that can be found at work desk location - up to Gigabit Ethernet.

I'd say more like 99% or more when discussing workstations at desks. Server to server I'd go with 90% - 95%.

Thanks every to every one who gave professional replies. It's easy to reference web pages and books but personal experience is much better. So, thank you again.

Thanks to every one who gave professional replies. It's easy to reference web pages and books but personal experience is much better. So, thank you again.

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I wasn't really familiar with PoE until now... Most of the VoIP telephones I've heard advertised on TV don't work when the power goes out. will PoE solve that problem or is that something different?

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Thanks.

This stuff is pretty interesting, I'm still not totally understanding though...

When you say "cable sharing applications" do you mean that it would be run broadband/analog?

Also, if I were a consumer, what types of applications would I need to use "balanced high-frequency signals" for.

thanks.

If you put the box that is providing the power on UPS, yes.

Doug Davis wrote in part:

This is not a simple question. Analog signals can carry digital data. And digital signals can carry analog data. The type of signalling chosen depends on the transmission medium. I have never heard of analog through glass fiber nor digital RF signalling.

Future TV? Convergence could come from the other direction. Today TVs are fed broadband signals (sometimes with digital data). A future system might well have a central PVR/decoder/gateway with monitors slaved off it.

-- Robert

PoE is not very widespread in home or small office installation. It is rather a "business" thing, that's why you will not see it advertised on TV too soon - the equipment is rather expensive for a small installation.