[1971] in linux-net channel archive
Re: Networking without a hub or a router/repeater(was Re: ``Networking'' via SCSI)
daemon@ATHENA.MIT.EDU (Paul Gortmaker)
Sat Feb 24 21:42:34 1996
From: Paul Gortmaker <gpg109@rsphy1.anu.edu.au>
To: lincoln@netapp.com (Lincoln Myers)
Date: Sat, 24 Feb 1996 12:57:15 +1100 (EST)
Cc: linux-net@vger.rutgers.edu
In-Reply-To: <9602222041.AA19440@nova.netapp.com> from "Lincoln Myers" at Feb 22, 96 12:41:50 pm
"Lincoln Myers" at Feb 22, 96 12:41:50 pm:
> According to the Ethernet-HOWTO, one twists 1&2 and 3&6, not 1&2, 3&4,
> 5&6, and 7&8 as one might interpret this. See the Ethernet-HOWTO.
Yes it is crucial that you *don't* just stick the wires into the plug
in 1,2,3,4,5,6 order and crimp it down. We had a technician here make
about a hundred or so patch cables that way, and he couldn't figure out
why the longer cables wouldn't work. :-) Of course he tested all the
cables at DC levels (0Hz). Poor guy learned the hard way.
You can get a bit sloppy with 10MHz, and even get away with mistakes
like the above over 1m distances, but the higher losses at 100MHz will
not let you get away with any shoddy wiring practices.
> I was told that 100-base-TX can use a null cable with the same pinouts
> (i.e. the same (high-grade) cable could work for both 10bt and 100tx).
Yes, that is what Donald used to test some of the early 100Base-T cards
(and drivers) when a hub wasn't available for a reasonable price.
> By the way, why is there no "100-base-2" (100mbit hubless thin
> ethernet equivalent)?
I don't have the specs here for RG-58 coax, but at 10MHz you can run
a signal 185m (max 10B-2 segment) and still get a signal out the other
end with less than about 10 dB loss. Now if you up the frequency to
100MHz, the loss of RG-58 scales dramatically, and only short runs
would be possible without suffering complete signal loss. Somebody
with the specs handy can post how many dB/m you lose with RG-58 at
both 10MHz and 100MHz.
Not to mention that the extra robustness of a star topology (single
branch failure vs. complete net failure) and ease of debugging make it
the choice of all but hobbyists and small/home installations.
Paul.
