RE: E1 - RJ45 pinout with ethernet crossover cable

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1

From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu]On Behalf Of
Sam Stickland
Sent: Friday, February 25, 2005 6:26 AM
To: nanog@nanog.org
Subject: E1 - RJ45 pinout with ethernet crossover cable

Hi,

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).

If I understand you correctly, you can eliminate the coax
altogether with a standard t1/e1 cable betweem the dsu's:

  1 2 3 4 5 6 7 8

RX Tip RX Ring n/c TX Tip TX Ring n/c n/c n/c

Just for reference, here's ether xover:

Crossover Cable (EIA/TIA 568A)

RJ-45 PIN RJ-45 PIN
1 Rx+ 3 Tx+
2 Rc- 6 Tx-
3 Tx+ 1 Rc+
6 Tx- 2 Rc-

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

Not that I know of, but I've never attempted what you
describe. Putting the baluns in the loop will destroy the
framing i.e. it's going to try and convert b8zs/ami to 802.x.

[ SNIP ]

-M<

2

How does a balun destroy the framing (or rather line coding)? It's just a
pair of transformers, and hence AC characteristics pass through intact.
All you've done is converted impedance (and, IIRC, line voltage).

Alex

3

Not that I know of, but I've never attempted what you
describe. Putting the baluns in the loop will destroy the
framing i.e. it's going to try and convert b8zs/ami to 802.x.

A Balun (BALanced to UNbalanced) is simply an impledence matching mechanism.

Crossover is still required.