[GRLUG] CAT5 Cables

[Greg Folkert]

On Wed, 2008-04-30 at 08:56 -0400, Adam M. Erickson wrote:
> I apologies if writing about cables on a LUG sight is upsetting
> anyone, I just have to inform anyone who might not know.
> 
> Cat5 Crimper $20, Cat5 Ends $7,  500' Cat5 Cable $50, - If you
> purchased these at Lowe's you could always make it yourself.
> 
> It is a good investment:
> 
>  1. If a end breaks you just have to crimp on another end.
>  2. Make the exact length that you need.
>  3. Could you find a crossover cable on the weekends?
>  4. Make a cabling for your friends and family, or just the people you
> really care about.
>  5. Lowe's is open on the weekends.
>  5. "Save Money"
> 
> Same amount of supplies and tools would cost $400 dollars for a kit at
> Best Buy and $700+ at best buy for prepared lengths that = 500'.
> Stores sell there cables for $17-$30 for about 20' of cable. It cost
> the same stores $2 to bring it in.

For those of us that manage wiring plants with bandwidth and EMI/RFI
guarantees, most of the time these guarantees require the use of
certified patch cables at both end of the link.

Is there any way *you* can guarantee these qualities in you self made
cables are within the certified limits for a given professionally
installed wiring plant:

     1. Impedance load
     2. Capacitance load
     3. Resistive load
     4. Contact end integrity for Attenuation (contact signal drop),
        NEXT (Near End Crosstalk) and PSNUM (Power Sum Crosstalk)
     5. Stress reliefs on each end to ensure cables don't bend more than
        a certain arc.

There are qualities, though these are the big ones.

At CAT3 (10Mbit and 16Mbit token ring) these really don't matter much
(Voice and up to 20MHz clocking).

As CAT4 and CAT5 don't exist in the real world, no matter.

At CAT5e, these begin to matter, at 125MHz clocking (100Mbit Ethernet
use 4/5 encoding), things like Impedance and Capacitance begin to
interfere with signaling. Impedance affect the ultimate distance an
"Ethernet" signal can travel, though a cable with capacitance can
literally short the signal via RFI crostalk between each wire. CAT5e
generally has greater twist in the pairs and twisting of the 4 pairs as
they go down the cable to combat both this capacitance and also to
thwart EFI/RFI outside interference. CAT5e is really the last of the
cabling you and I can make that work. CAT5e cables are generally good
upto 150MHz, but not are guaranteed, some do work for 1GBit, but lots of
re-tries and drops do occur. On 1GBit, it uses all four pair of cable to
"mux" the signals, and get the throughput up. vs 100Mbit, only using 2
pair. CAT5e can be usable upto 250Mhz.... but Your Mileage May^H^H^H
*WILL* Vary GREATLY.

At CAT6 and beyond, typically ONLY are possible to be made in a
manufacturing environment. Why? Tolerances required are not repeatable
except in jigs and machines set to certain "crush torque" and stripping
of wire without nicking them and so on.

(yes these links are wikipedia, but they are correct and point to good
references)

http://en.wikipedia.org/wiki/Category_3_cable
http://en.wikipedia.org/wiki/Category_5e_cable
http://en.wikipedia.org/wiki/Category_6_cable

http://en.wikipedia.org/wiki/Structured_cabling
http://en.wikipedia.org/wiki/TIA-568B

-- 
greg at gregfolkert.net
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