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


I believe that there are several other reasons.
One significant one is added cost
Another is that most 1000BASE-T devices will not operate within the power 

Few low power devices will need 1 gig of bandwidth. Nothing comes to mind 
at the moment


At 08:14 AM 3/19/02 -0500, Rehan Mahmood wrote:
>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
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