E1 - RJ45 pinout with ethernet crossover cable

Fri Feb 25 12:03:52 UTC 2005

--On 25 February 2005 11:57 +0000 Per Gregers Bilse 
<bilse at networksignature.com> 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).
>
> You generally need a router or something else acting as store-and-forward.
> E1/T1 and other plesiochronous circuits are just that, near synchronous,
> and certainly not asynchronous.

Whilst this is true, his question still stands. Yes indeed if you got the
RJ-45 crossover right (I don't think it's ethernet pinout from memory,
but...) you would indeed achieve the same effect as a crossed over pair of
coaxes. However, it might well not be the effect you intend or desire (for
the reasons Per points out).

One circumstance where this does work is connecting (for instance) an E1
trunk connection between (say) two FR switches in the same room, provided
you remember to set exactly one end to originate, and one end to receive
clock (i.e. where there are no carriers involved).

Alex