Re: Gigabit network

[David Yeend <david.yeend@xxxxxxxxx>]

802.3AF (upper-case to signify that it is an official standard)
defines both modes - 'spare pairs' and 'used pairs'. A device does not
have to offer both forms to be compliant with the standard.

Mid-Span injection - which is what you have to use to 'add' power to a
switch port only works in the 'spare pair' mode and is therefore not
applicable to 1000BASE-T.

The only way PoE will work for 1000BASE-T is where the PSE is combined
with the switch. As 1000BASE-T is typically used for switch to switch
links and switch to server links it is not that common to find PoE
equipped 1000BASE-T.

You are quite right about there being a lot of non 802.3AF compliant
'PoE' injectors/splitters which simply use the spare pairs of cat5 to
carry power to a device. Also, as you say, they do not offer any of
the safety of power class signalling mechanisms offered by the 802.3AF
standard.

Just to pick up on one point made earlier on in the thread - many
'non' enterprise class Gigabit switches which I have seen offer
10/100/1000 on their copper ports provided they are not connected via
GBIC/SFP. The quality of products at that end of the market is now
very good.

Regards,

David