[78238] in North American Network Operators' Group
Re: E1 - RJ45 pinout with ethernet crossover cable
daemon@ATHENA.MIT.EDU (Jay Hennigan)
Fri Feb 25 11:56:02 2005
Date: Fri, 25 Feb 2005 08:55:10 -0800 (PST)
From: Jay Hennigan <jay@west.net>
To: Per Gregers Bilse <bilse@networksignature.com>
Cc: Sam Stickland <sam_ml@spacething.org>, nanog@nanog.org
In-Reply-To: <200502251157.j1PBvEx30580@spirit.qbfox.com>
Errors-To: owner-nanog@merit.edu
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 - jay@west.net
WestNet: Connecting you to the planet. 805 884-6323 WB6RDV
NetLojix Communications, Inc. - http://www.netlojix.com/
