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

[802.3af] Liaison report from ISO/IEC JTC 1 SC 25/WG 3 on mid-span power

Hello Geoff,

Do you think because of not having enough interest we are not considering 
1000BASE-T for Midspan PSE?


Rehan Mahmood

Geoff Thompson <gthompso@xxxxxxxxxxxxxxxxxx> 03/18/02 10:00AM >>>

Your most recent question is a little different than your personal question=
that was covered on the cover page of the liaison letter.

The position of the current draft is that.
        If power is being inserted on the cabling from the switch/repeater =
towards the DTE (i.e. not mid-span insertion) then either the pairs on pins=
1-2, 3-6 (Alternative A) or the pairs on pins 4-5, 7-8 (Alternative B), bu=
t not both.
        If the power is inserted on the cabling with a mid-span then the pr=
oposed standard mandates Alternative B.

The normal expectation is that the pairs used for power in a mid-span would=
not provide continuity through the mid-span. Those pairs on the unpowered =
side of the mid-span are expected to be unused but properly terminated. Thi=
s is not mandated, however. The draft states in 33.2.2 that:
"Midspan PSE must use alternative B as described in section 33.2.1.Midspan =
PSE are limited to operation with 10BASE-T and 100BASE-TX systems,1000BASE-=
T is beyond the scope of this standard."

So it may be possible to build a Midspan PSE that would serve 1000BASE-T. M=
any people think this is possible. We have not investigated it during this =

I hope that provides a definitive answer to your question.

Best regards,


At 08:10 AM 3/16/02 +0100, Pattay Walter wrote:

Dear Geoff,
thanks for this quick answer that - if complete and future proof - makes
life much easier.=20
But to be on the safe side, let me confirm explicitly: there is no need for
us to consider mid-span-power insertion for applications using all four
pairs for information transfer.
Kind regards

Send and receive Hotmail on your mobile device: