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Re: E1 - RJ45 pinout with ethernet crossover cable

  • From: Per Gregers Bilse
  • Date: Fri Feb 25 06:59:39 2005

On Feb 25, 11:25am, Sam Stickland <[email protected]> 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.  Things cannot be transmitted or received
without clocks on both sides being in synch, which may or may not be the
case if you try to hook up two arbitrary lines.  Moreover, assuming both
are terminated towards you, both will be driving clock for your router
("terminal equipment") to pick up, and they are not going to be in phase.
Then there's the issue of different options for framing and various
control bits, etc.  You might get lucky if you could convince one of the
circuit providers to take clock from you (which would then come from the
other circuit), but you would probably still need to deal with signal
level, framing, and other issues (ie, have a box of sorts).  All in all,
an old cisco 2500 is probably the cheapest and most troublefree solution.

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

It's balun -- BALance-UNbalance.


  -- Per