Re: [8023-POEP] What's the max voltage drop thru a midspan?
Hi Steve,
I see your point but the text states that the Mid-span 'shall not alter
the transmission requirements of the permanent link.' so it really depends
if the DC Current carrying capacity and the Resistance are considered
'transmission requirements' or not.
Regards,
David
owner-stds-802-3-poep@xxxxxxxx wrote on 12/06/2006 16:00:15:
> David,
> Unfortunately I don't think this text solves the problem. My
interpretation
> is that it does the following:
> 1. The midspan must pass data thru it without degrading data integrity.
> 2. As the midspan injects power on the spare pares, it must block that
> power from going back to the endspan.
> So it doesn't say anything about passing power thru on the data pairs.
> Steve
> -----Original Message-----
> From: owner-stds-802-3-poep@xxxxxxxx
[mailto:owner-stds-802-3-poep@xxxxxxxx]
> On Behalf Of David Law
> Sent: Monday, June 12, 2006 3:46 AM
> To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
> Subject: Re: [8023-POEP] What's the max voltage drop thru a midspan?
> Hi Steve,
> Do you think the following text contained in the third from last
paragraph
> of subclause 33.4.8 'Midspan PSE device additional requirements' of IEEE
> Std 802.3-2005 covers what you are looking for:
> ---oo000oo---
> Configurations with the Midspan PSE in the cabling channel shall not
alter
> the transmission requirements of the "permanent link." A Midspan PSE
> inserted into a channel shall provide continuity for the signal pairs. A
> Midspan PSE shall not provide DC continuity between the two sides of the
> segment for the pairs that inject power.
> ---oo000oo---
> Regardless, I agree that the IEEE 802.3at specification will need to be
> written carefully to ensure that, for example, it doesn't
retrospectively
> place a higher current carrying requirements on existing IEEE Std
> 802.3-2005 compliant Mid-Span PSEs.
> Regards,
> David
>
> owner-stds-802-3-poep@xxxxxxxx wrote on 10/06/2006 05:34:39:
> > Guys,
> >
> > As you all know, we're planning to run current from the endspan thru
the
> > midspan in a 4P system.
> >
> > Although I think its unlikely that we'll see Af-midspans with fused
> traces
> > or delaminated boards, technically we can't prove that it won't happen
> > because 802.3af doesn't specify a min current rating for this path.
> There
> > seems to be no max limit for dc resistance either. (If these specs
are
> in
> > 802.3af and I've missed them, then someone please point me to the
> applicable
> > table or paragraph.)
> >
> > We should make sure 802.3at specifies both these parameters. (But
only
> for
> > midspans that output >15.4W so we're not retroactively putting new
> > requirements on Af-midspans.)
> >
> > Any comments?
> >
> > Steve
> >
> > [attachment "C.htm" deleted by David Law/GB/3Com]