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Re: E1 - RJ45 pinout with ethernet crossover cable

  • From: Jay Hennigan
  • Date: Fri Feb 25 11:57:13 2005

On Fri, 25 Feb 2005, Per Gregers Bilse wrote:

> 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.

In every case I've dealt with when  setting up a back-to-back connection
of T1 or E1 circuits, the appropriate crossover connection between transmit
and receive (1,2 - 4,5 on 8-pin jacks, swap Tx and Rx on co-ax) and setting
one side to supply internal clock and the other side to recover clock from
line works just fine.

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