[TriLUG] OT: Home Depot and Cat 5

Joseph Mack mack.joseph at epa.gov
Tue Oct 5 12:44:29 EDT 2004


Steve Litt wrote:

> I have an additional question. I have a 150' cat5 cable hand made by my
> vendor. It doesn't work. A friend told me that with long runs there's a
> special wiring method than with short runs, in order to limit capacitance or
> inductance or some such.

it's hooey. 4 pair 100Mbps ethernet over cat5 is spec'ed to a bit over 100m. 
There's only one way to wire it up.

You can buy tester boxes which look like a pair of phone handsets clipped 
together - you put one at each end of the line and it tests
for electrical continuity for all 4 pairs (and tells you if the polarity
is wrong etc). They were about $80 a few years ago. This test doesn't tell
you whether they will work at 10Mbps or 100Mbps. There's expensive testers
for this, but plugging the cable into two computers with NICs that are known
to work does the test at no charge (do a ping). All cables I've had that passed 
the DC continuity test also carried the 100Mbps packets as well. I have several
100m cables that work just fine (no lost packets), so presumably 100Mbps 
can go further than the spec on cat5. For distances further than 100m, 
I use a hub/switch/something to reform the packets and send them on 
their way again.

Joe

-- 
Joseph Mack PhD, High Performance Computing & Scientific Visualization
LMIT, Supporting the EPA Research Triangle Park, NC 919-541-0007
Federal Contact - John B. Smith 919-541-1087 - smith.johnb at epa.gov



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