[159092] in North American Network Operators' Group
Re: Fiber only in DataCenters?
daemon@ATHENA.MIT.EDU (Matthew Kaufman)
Fri Dec 21 11:53:44 2012
Date: Thu, 20 Dec 2012 15:20:18 -0800
From: Matthew Kaufman <matthew@matthew.at>
To: joel jaeggli <joelja@bogus.com>
In-Reply-To: <50CF54C0.9010106@bogus.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On 12/17/2012 9:22 AM, joel jaeggli wrote:
> If the facility is big enough the utility of twisted pair becomes
> quite limited, both due to distance and differing electrical
> potential, multibuilding campuses in particular make this is a
> nonstarter.
For twisted-pair Ethernet: Distance yes. Differing electrical potential
no. It is a balanced pair, transformer coupled at both ends. As long as
AC common-mode pickup doesn't saturate the transformer core, it just works.
>
> In one facility I'm in, I'm over 300 meters from each of the MMRs,
> with the results that the OOB for the serial console server for out
> equipment located out there in the MMR's being on serial over fiber
> transceivers connected by om4 multimode.
RS232 serial is another story. Here the potential difference between the
ends is a big deal. (I've even seen burned-through PC boards from what
happens when pin 7 has 220 VAC flowing from one device to the other) But
you can just run Ethernet out to the console server and plug it in next
to the gear with the serial port to fix this.
Matthew Kaufman
