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Re: E1 - RJ45 pinout with ethernet crossover cable

  • From: Jay Hennigan
  • Date: Fri Feb 25 12:21:43 2005

On Fri, 25 Feb 2005, Sam Stickland wrote:

> Quick question: If I have two E1 ports (RJ45), then will running a
> straight ethernet cable between the two ports have the same affect as
> plugging a ballan into each port and using a pair of coax (over a v.
> short distance).

Not straight, you need to make or buy a special crossover cable unless
you're going from a CSU to a terminal equipment port, in which case a
straight cable will work if it has all four pairs connected.  Some cheap
cables sold for ethernet use only have pairs 1,2 and 3,6 wired.  These
will not work as T1/E1 uses 1,2 and 4,5.

> Likewise would using an ethernet crossover cable have the same affect as
> swapping the pairs round on one balland.

I think you mean "balun".  A crossover cable for T1/E1 is pairs 1,2 and
4,5 swapped which is blue/white and green/white for 568A.

> Or are the pinouts different to ethernet? I tried googling but couldn't
> find anything (perhaps because I can't seem to spell ballan :/ ).

Well, the modular jack connections are balanced and coaxial cable is
unbalanced.  You don't need baluns unless you're going from BALanced
on one end to UNbalanced on the other (hence the name balun).

Get a straight-through cable. and look at it.  If the insulation on the
left two pins is green when holding the contacts up and away from you,
then cut off one end and reassemble it with the green and blue pairs
swapped around.  If orange, then swap the orange and blue.  If brown, turn
it over and look again.  :-)

Set ONE of your devices to provide clock ("Internal") and the other to
recover clock from the line ("Network").  If either of the devices is
also connected to a carrier or other network by T1/E1, clocking can get
more complicated and you probably want to consult a local expert on that
particular equipment.

Jay Hennigan - CCIE #7880 - Network Administration - [email protected]
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