AS/400 9404 and TWINAX questions...

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Mon Sep 27 16:17:53 2004

> Good news: You could even make an Ethernet/Twinax single jack, if you're
> not running faster than 100Mbps ethernet, as they run 1/2 & 3/6 for their
> pairs -- just use 4/5 for twinax.
>
> Bad news: *Most* pre-built cables don't follow the standard as to where the
> twisted pairs should be - most just go 1/2 - 3/4 - 5/6 - 7/8 - and that's
> bad for both Ethernet & twinax. You'll wanna punch down and/or build your
> own cables if you're going to do this.

What?!?!?

I've made the odd 10baseT patch lead, and I was always careful to get 1/2
as a pair and 3/6 as another pair (I think the other 2 pairs were 4/5 and
7/8, but it;s been a long time..) Fiddling the wires into the RJ45 was a
pain, but I assumed it was necessary....

And you're telling me commercial cables get it wrong. I knew there was a
good reason to avoid them [1], the time in making up a cable is much less
than the time to sort out network problems later

[1] Other horrors include the IEC mains cable with L/N swaps, one I saw
with N/E swap(!), the null modem adapter which couldn't have worked with
any normal pair of RS232 devices (4 strapped to 5 at each end _and_ those
linkled across the adapter, that will short 2 outputs together...), an
RS232 cable that used the cable screen (shield) as one of the handshake
lines (!), and so on...

-tony
Received on Mon Sep 27 2004 - 16:17:53 BST