Re: Machines not communicating

From: Jed Clear (clear_at_alum.mit.edu)
Date: 10/03/04 

Date: Sun, 03 Oct 2004 14:01:23 GMT

Wes Groleau wrote:
>
> Tim Daneliuk wrote:
> > Perhaps you have a bad cable. Have you tried using a known
> > working cable to connect the machine that is not working?
>
> Yes and no. Before I got the switch, BSD2 was a usually OFF
> backup machine. Occasionally, I took the crossover cable
> off iMac and moved it to BSD2 (leaving the other end on BSD1)
> Communication always worked between the two BSDs when I did that.
> I am going to try it again when I catch up on my homework.
>
> That's the cue for "Why are you posting to Usenet instead
> of doing your homework?" :-)
>
> But doesn't carrier detect imply a good cable?

Not necessarily. I found a Cat 5 cable with RJ45 connectors in our lab
when I was setting up a new workstation. It was a straight through
cable, and carrier came up when I installed it. Wouldn't transfer data
at all. I dug out an ohm meter and it looked OK. Turned out it was not
pinned according to EIA-568A/B. The twisted pairs were not 1-2 3-6. I
think they were 1-2 3-4 although at that point I put it back in the
cabinet for the next victim.

The point being you can't just look at which solid color is in which pin
at either end, but you need to try to figure out which striped white
wire is where, which can be difficult.

http://www.ablecables.com.au/568avb.htm

-Jed