[802.3af] Re: AW: Liaison report from ISO/IEC JTC 1 SC 25/WG 3 on mid-span pow er insertion
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.
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), but not
power is inserted on the cabling with a mid-span then the proposed
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. This is not mandated, however. The draft states in 33.2.2
"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. Many people think this is possible. We have not investigated
it during this project.
I hope that provides a definitive answer to your question.
At 08:10 AM 3/16/02 +0100, Pattay Walter wrote:
thanks for this quick answer that - if complete and future proof -
life much easier.
But to be on the safe side, let me confirm explicitly: there is no need
us to consider mid-span-power insertion for applications using all
pairs for information transfer.
Von: Geoff Thompson
Gesendet am: Sonntag, 10. März 2002 06:31
An: Pattay Walter
Cc: Alan Flatman; scarlson@xxxxxxxxxxxxx; thompson@xxxxxxxx;
Betreff: Re: Liaison report from ISO/IECJTC 1 SC 25/WG 3 on mid-span
We will review your Liaison at our meeting in St. Louis during the
Re: your text on the cover of the Liaison Letter:
Due to the discussion in Kyoto it would be important for WG 3 to
know whether mid-span power insertion will always use separate
pairs, that is pairs which are not used for information transfer or
whether there is also a need to provide this function for pairs
for information, e. g. when only two pairs are terminated at the
The next meeting of WG 3 will take place near Washington,
D.C., USA, 2002-09-23/26.
The answer to the above question is as follows:
Mid-span will always use separate pairs.
End-to-end may use either the data pairs or the "separate
pairs" but not
Therefore, mid-span may not be used in a situation where only 2 pairs
terminated at the TO
I hope to be able to attend the upcoming meeting in the Washington,
At 11:36 AM 3/6/02 +0100, you wrote:
please receive the liaison report as it was approved at our last meeting.
Unluckily we were short of time - as usual - and not all the output
created on this subject was found complete or ripe enough to be
to you in this report.
We definitely will do some more work on this subject at our next meeting.
the outcome may be an interface to generic cabling in addition to
defined in the present model, it promises to be a challenging
Hoping to see you there again I remain with best wishes
| Geoffrey O.
| Nortel Networks, Inc. M/S
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