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RE: [802.3af] Link negotiation

I understand the issues associated with using link as a mechanism for
turning off power however I can't think of another way other than what Yair
(detect the capacitance) has suggested. I'm still working my way through the
capacitance approach and at present don't have an opinion as to its


		-----Original Message-----
		From:	Scott_Burton@xxxxxxxxx
		Sent:	Friday, December 21, 2001 3:46 PM
		To:	stds-802-3-pwrviamdi@xxxxxxxx
		Subject:	RE: [802.3af] Link negotiation

		From:  Scott Burton@MITEL on 12/21/2001 06:46 PM
		I was curious as to the lack of discussion as well. Has
interest in this topic
		faded due to some
		decrease in interest in an alternate power removal detection

		"Eric Lynskey" <elynskey@xxxxxxxxxxx> on 12/21/2001 11:22:00

		To:   stds-802-3-pwrviamdi@xxxxxxxx
		cc:    (bcc: Scott Burton/Kan/Mitel)

		Subject:  RE: [802.3af] Link negotiation

		I am somewhat concerned that I have yet to receive a single
response to my
		original email, or seen any discussion on the email that
Scott Burton sent
		out on the 11th.  Does anyone have any other input on what
to use as the
		disconnect detection method, or to better explain the text
		associated with this method?  Is anyone planning to provide
a comment
		against the current draft?  My guess is that at least one TR
should be
		submitted against this.  Can anyone else offer some


		-----Original Message-----
		From: owner-stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx
Behalf Of Eric
		Sent: Friday, December 07, 2001 2:23 PM
		To: stds-802-3-pwrviamdi@xxxxxxxx
		Subject: RE: [802.3af] Link negotiation

		This is really the first time I've looked at the draft, but
your email below
		does bring up some interesting points.  Any device that is
		auto-negotiating will, upon reset, send nothing for 1.2 -
1.5 seconds.  This
		is referred to as break_link_timer.  During the
auto-negotiation process, a
		device will be sending FLPs, but will not be in the LINK_UP
state, and
		therefore will not be providing PD_DATA_LINK to the PSE.
		auto-negotiation process does take several hundred
milliseconds, and this is
		prolonged if a device is negotiating a 1000BASE-T link.  On
average, if the
		PD is reset, 2 to 3 seconds could elapse before it returns
to the
		PD_DATA_LINK state.  The standard does not put a limit on
the number of
		pages that can be sent during the auto-negotiation process,
and therefore it
		would be hard to put an upper limit on this.

		It's not clear from my reading of that section what exactly
a PD should do
		in order to stay powered.  Does it send 10BASE-T link test
pulses?  Does it
		send 100BASE-TX Idle?  Does it have to be able to support
both?  What about
		the PSE?  Does it need to recognize all methods?  If I have
a PD, such as
		the ethernet razor, it's not clear to me what I should be
sending in order
		to receive power.  Presumably I need to have some knowledge
of the PSE.  Is
		this correct?  Do I need to know whether I'll be plugging
into a 10, 100, or
		10/100 port?  This also applies for plugging into a
1000BASE-T port.

		I'm just curious what the intent is supposed to be.

		Eric Lynskey

		-----Original Message-----
		From: owner-stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx
Behalf Of
		Sent: Monday, November 26, 2001 10:48 AM
		To: stds-802-3-pwrviamdi@xxxxxxxx
		Subject: [802.3af] Link negotiation

		At the last plenary, we decided to allow PSE's to evaluate
		variable as a qualified for the power request signature.  We
added the
		requirement without modifying any of the timing parameters
and at least need
		provide a hold off time from power assertion to "link up"
since we need to
		recognize that PDs can't establish link without first
getting power.

		On return to my office I've checked with a few people more
		myself and have been told that link negotiation, on a proper
arrangement of
		cable and equipment, of 600ms has been observed in the lab
		time to establish "link up" does not include such real world
problems such
		plugging two 10/100/1000 devices together via a 100m of
CAT-3 cabling and
		letting things go their course.  I will take it upon myself
to try to dig
		values out of the 802.3 specification so that we can bound
what we are
		committed to, but I'd like to hear form others with real
world experience or
		knowledge of what their PHYs were designed to.

		There are other real world considerations, such as OSs which
routinely reset
		their MAC chips after the BIOS has already enabled them and
cause "link" to
		out.  It would also appear the my Windows98 PC resets the
MAC when I run
		Winipcfg and ask it to release and renew all (it looks like
the link LED
		flickers, I need to check with an analyzer.)  These types of
behavior would
		cause units to get powered down in the middle of otherwise

		I'd suggest we scrutinize what we have really done when we
say that PDs must
		maintain the "PD_DATA_LINK" variable.