[asterisk-users] Crossover cable for E1 ?

[Tilghman Lesher]

On Monday 24 January 2011 03:46:18 A J Stiles wrote:
> On Saturday 22 Jan 2011, Tim Panton wrote:
> > I'm looking to connect a BMC 450 to an asterisk with a Digium Quad E1
> > card.
> > 
> > Am I right in thinking that I'll need a special 'crossover-E1' RJ45
> > cable?
> > 
> > If so, any clues where I might buy one in the UK? The Digium card
> > sellers don't seem to stock such a thing.
> 
> It's easy to make an ISDN crossover cable.
> 
> Cut one end of a standard network cable.  Get a new RJ45 plug, rubber
> boot (not strictly necessary, but makes it look neater)  and crimping
> tool.  Push the rubber boot onto the end of the cable first.  Strip
> about 2cm. of outer sheath and separate the inner pairs, then arrange
> in this order from left to right with the brass contacts uppermost:
> 
> white/blue blue white/green orange white/orange green white/brown brown

This is incorrect.  The pairs should be:

blue white/blue white/green white/orange orange green white/brown brown

Wire 1 MUST swap with 4 and Wire 2 MUST swap with 5.  To do as you have
shown above switches the polarity on each electrical circuit.  It is
especially important that you do not switch the polarity, as some equipment
does not auto-correct for reversed polarity.

-- 
Tilghman