Fiber only in DataCenters?

Matthew Kaufman matthew at
Thu Dec 20 23:20:18 UTC 2012

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

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