Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: [8023-POEP] What's the max voltage drop thru a midspan?



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]