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RE: detecting a PD disconnection event

Hi Yair

I totally agree with Rick on the matter.  we do not want to affect someone's
Intellectual property as a standard.  if someone elects to go the dc route
in their PSE that is their choice.  
basically we do not dictate what can not be done...
we should have alternatives to doing this unlpug-detection in a way that
respects someone's IP, when and if it applies...

my 2c.


At 08:47 AM 4/30/01 -0700, Rick Brooks wrote: 

> Yair, 
> there are a few comments below. 
> In general, I am making this proposal so that the 802.3af spec will not run
> directly against 
> an existing patent not matter how fond we are of DC minimum current. 
> I am not judging the patent at all, except to comment that it appears to have 
> some validity pertaining to UTP data networks. It would be unwise to ignore
> it. 
> If anyone can find prior art, then great. In the meantime we cannot and
> should not discuss any legal 
> or patent validity issues. I suggest we simply consider the alternatives in
> case we must use them. 
> The sole reason to detect an unplug is to shut down power so that other RJ-45
> devices will not 
> be damaged. Therefore, we could allow a few different detection methods for
> an unplug event and still meet this goal.  
> -----Original Message-----  From:   Yair Darshan [SMTP:YairD@xxxxxxxxxxxxxx] 
> Sent:   Saturday, April 28, 2001 5:00 PM  To:     Brooks, Rick [SC5:321:EXCH];
> stds-802-3-pwrviamdi@xxxxxxxx  Subject:        RE: detecting a PD
> disconnection event 
> Rick, 
> For 1) The PSE should disconnect power from the port within 400mSec. 
>  Reason: Lab tests shows that fast technician can not disconnect PD  with
> non-PD device and cause damage.            It is also suggested that within
> this time, the average port  voltage will be 5V max. (to limit PSE output port
> capacitor energy)  [Brooks, Rick [SC5:321:EXCH]]   
> That sounds good to me. The definition would be that the maximum time from an
> "unplug" action 
> until the PSE out goes to 5V or below is 400ms. Of course, we all need to
> discuss these  numbers. 
> For 2) The easiest way is to measure the current and disconnect the port 
> voltage if the current is less than 10mA for more than TBD msec.           
> Actually the PSE should disconnect in less than 5mA, and may or  may not
> disconnect between 5 to 10mA. These values allows simple sensing  circuit 
>       which we need any way for the overload protection. 
>          The other method like checking the Ethernet link has few drawbacks: 
>         1. It can not be supported by Midspan.           2. What will happen
> if the PD is connected to external source  voltage and you still have link,
> however the PSE is still delivering power  and it should not.  [Brooks, Rick
> [SC5:321:EXCH]]   
> These are good points.  
> See more comments below. 
> Yair. 
> > -----Original Message-----  > From: Rick Brooks
> [SMTP:ribrooks@xxxxxxxxxxxxxxxxxx]  > Sent: ו, אפריל 27, 2001 5:58 PM  > To:  
> stds-802-3-pwrviamdi@xxxxxxxx  > Subject:      detecting a PD disconnection
> event  >  > Just to start up another discussion, I wanted to find out how many
> people  > would support  > the following concept for detecting when a PD
> receiving power becomes  > disconnected.  > > the concept: >
> $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ > > 1)
> The PSE is responsible for detecting when a PD receiving DTE power  > becomes
> disconnected.  > If that event occurs, the PSE must turn off the power within
> some time  > frame (100ms to 500ms ballpark?)  > > 2) The PSE may use any of
> the following methods to detect this PD  > disconnect event.  > >         a)
> the DC load current drop below "X" ma (10ma?)         [Yair Darshan]  See
> above. 
> >         b) the ethernet link has dropped out          [Yair Darshan]  See
> above. 
> >         c) another proven method (pending discussion and feasibility  >
> proof)  >                 some suggestions: >                 1) the AC
> probing circuit detects when the AC load changes  > (opens)          [Yair
> Darshan]  It is sensitive to noise. DC methods are more  reliable.  [Brooks,
> Rick [SC5:321:EXCH]]   
> The possible use of something like synchronous detection could help here.  
> >                 2) the PD modulation heartbeat current ceases          [Yair
> Darshan]  Not clear?  [Brooks, Rick [SC5:321:EXCH]]   
> This means that the PD would have a small circuit that produces a periodic
> current modulation. 
> The PSE has a watchdog timer that must always see the periodic current or the
> power shuts off.  
> >                 3) the PD response to a given PSE code is wrong or absent 
>       [Yair Darshan]  This is related to false detection, and we need some 
> thing unique for disconnecting.  [Brooks, Rick [SC5:321:EXCH]]   
> I am assuming that this is independent of discovery, a different mechanism,
> and therefore not related 
> to false discovery.  
> >                 4) other ideas  > >
> $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ > > >
> Please voice your opinions on this concept. > The motivation here is to lower
> the cost of delivering DTE power. > > thanks, > - Rick >