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Dan- Again

Hi Dan
thank's for your input and 
here is my 2c on this.

>>    Thank you for asking- I am encouraged.
>>  Cisco's proposal has the following A, B sections.
>>  A- Use the Signal pair 1,2 and 3,6 to deliver power on a new switch.
>>  B- Use unused pair (4,5 and 7,8 ) to deliver power for mid-span.
>Intuitively, this seems to add complexity and I can not fathom
>why we would want to use different pairs depending on the 
>location of the power insertion. Given our objective of detecting power on
>the same pairs that it is inserted, this would require twice the amount of
>DTE-detection circuits and raise the issue of how to deal with switch vs
>mid-span insertion conflicts (ie: The switch sends Fat-Link-Pulses down
>12,36 and gets confirmation to send power while the mid-span sends its
>signals down 45,78 and gets confirmation on its pairs). This sounds like
>un-necessary complexity.

Dan, a bunch of things here,


1- we have yet to prove that going with the signal-pair (1,2 and 3,6) in Mid
   span is a problem.  We all think that it is risky based on common sense.
    and chances are it could be. Fine and dandy for exisiting switches at
    customer sites, we are not about to have them removed as some people claim.

2- why the signal pair, and why NO complexity:

a- there will be some customers with 2-pairs only, may be x% but there will be some.
   and telling them look Mr customer, you did not follow the IEEE rules so
   now you have to pay  does not sound like a valid reason to him and sounds like
   a punishment to me.....

b- When I think about what it takes to do this standard, I envision a low entropy spec
    where the scheme should be simple, clean and  does not require heavy duty
    PHY-like level of intensity.  after all some  pulses will flag a DTE (phone say), you turn
    power on, making sure that nothing will be fried ( & transient protection....).

c-  many little reasons come to mind so here is a Top 10 list:

    So if we are selling a NEW switch, 

    1- the intelligence for power and management can be in the switch 
    2- the customer does what he always did, just plug and play 
    3- less boxes and headaches at the patch panel
    4- I as the wire-side engineer know that my circuitry is sitting behind
       2000 volts of isolation, esd protected, and very possibly inside the phy
       leaving me with a single Monitor-part at maximum and possibly little silicon if I had 
       my way here at the wire-side! to do the JOB.

       I am talking about zero circuitry on the board ( probably) for detection and a few
       parts for power delivery. (transient protection and a power monitor)

    5- the minute you require a lot of intelligence to be on the wire side and start to
        think too much silicon, and at low voltage, you will enter into what could be a silicon
        headaches in the field due to latch-up and transients.

    6- I hear everyone- there will be some us who want to fry eggs off the ethernet cable,
       charge batteries, but this differential scheme is begging to be used for ethernet-
       networking enviornment where these phy vendors that we all beat up daily, who learned
       so much over so many years the hard way, delivering some really challenging solutions
       can be of help to us (and this is  not to vote for any of them).
     I hear you, this is not optimal for the Egg cooker, but accomodating the egg cooker request,
      to me is the added complexity.  The majority of us are doing 10/100/1000 Ethernet
     So let's see both sides for a change.

  7- Gigabit Again 1000BT <> (not equal) to 1000BT, and it is either 1000BT/100TX /10BT
     or at least 1000/100, while  seeing each other can be fun every 2 month, brushing
     this aside as un-necessary at this point may not the best approach here,  since 1000BT
     makes signal pairs out of the 4-pairs in the cable, once we solve the signal- pair
     issues we may be in for an addendum to the spec (if we elect not to tackle it now)
     and we will not have to revisit this in 2 years.

8-  To this point, I am the optimistic one and feel good about this, what would be interesting is  if
     we all get in with an open mind and possibly improve it, it may get us somewhere, years and
    years of PHY, Magnetic, and RJ45 experience on our part and the vendors' can be put to make
    such an approach a reality with minimum extra space needed  on the switch (due to density) this will prove
    to be a blessing.   How much room are we left with at the RJ45 with high port count boxes,
    The phy will have to be there, so shove as much into it as we can.

9- Say we run into a situation where more power has to be delivered, and it is impeded by
     the Connector or wire, then having access to the 2 signal  pairs is a blessing.
     possibly allowing a power hungry device to be built.   

10- Again, drumming up the phy story, should this prove doable, and at this point I think
      that it is, then designing Detection into the phy might prove to be a good option that 
     is there for anyone to reach for.  We can look into this, it may be as simple as using
     2 switches to use along with the POWER monitor circuitry existing on the unused pairs- 
     plus the phy detection and there you get 2 schemes  in one.  Also If the DTE is built
     to accomodate a single approach that could prove enough, but the added flexibility may
     be 2-3 parts away.  So long that we try to keep an open mind.

These reasons are coming from myself and some of the issues that 
were raised at last meeting.   Of Course Larry's approach and yours have merit,
and your ideas possibly have advantages in some ways, let's look at each approach, at measurements,
and transients protection and see where this leads us to...  I want you to know that I have
toyed with the single ended approach, where common mode pulses are sent in/out of RJ45,
and worried about noise, EMI and silicon on the wire issues.



>If you are conceding that using the unused pairs for mid-span is a better
>alternative than using the data pairs, please explain to me why we should
>use the data pairs for switch-based power insertion.


>Simplicity, and consistency would argue that we should just apply power in
>the unused pairs at both locations and reduce the number of alternatives by
>Dan Dove
>HP ProCurve Networks