Re: Gigabit network

[Richard Malcolm-Smith <rich@xxxxxxxxxx>]

ian.bird@xxxxxxx wrote:

> Secondly, power over Ethernet is becoming popular with new embedded
> gadgets supporting it. It uses the 'unused' pairs in a 10/100
interface
> for the power. In the Gigabit world there are no unused pairs and you
may
> find that the majority of these 'new' devices cannot exist on this
faster
> network. There are ways round this latter point at the design stage
but I
> have not seen any devices advertising this ability.

802.1af supports 2 modes of delivery, and only one is over the spare pairs.
The
other has centre tapped transfromers in the magnetics, and uses that to
send DC
over the 2 pairs while they are being used for signaling. Any 802.1af
complient
device should accept power both ways, but the only thing that can supply it
on
the same pairs as the ethernet signal.

This is why the add ons you see for linksys and dlink are not actually
802.11af
power over ethernet, they are only able to use the spare pairs.


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