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Re: Selection Criteria for choosing a Discovery Method, Reply to Rick Brooks Note of 9/25/00



Title: RE: Selection Criteria for choosing a Discovery Method
Rick, when I proposed to maintain a list of pros and cons for the two discovery methods, I stated that the area that would be most controversial would be asssigning a value to the importance of each of the factors.  That determination I left for each of us to decide, so that we would not be in an endless battle on those fine points.  I think that your note provides us with good input, which we need to consider.  In an attempt to separate the listing of benefits from weighting the benefits, I would like to propose a melding of your input and Don's as follows: 
 
Don has recommended:
 
(I-2) Minimizes cross-talk interference potential to Gigabit Ethernet and
unidentified future services,
 
which you would like to see rewritten as:
 
(I-2) Does not interfere with Gigabit Ethernet
 
I would propose resolving this disagreement as follows:
 
Include the following distinctions:
(I-2a) Does not interfere with Gigabit Ethernet
(I-2b) Further minimizes cross-talk interference potential to Gigabit Ethernet
(I-2c) Minimizes cross-talk interference potential to unidentified future services
 
When listed in this way, each of us can make the independent assessment on how much weight to give the benefits of  not interfering with Gigabit Ethernet, with further minimizing cross-talk interference potential to Gigabit Ethernet, and with minimizing cross-talk interferfence potential to unidentified future services.  I-2b and I-2c may be  categories that Don gives a stronger weighting to than you do.
 
With this proliferation of catgegories, I would advise the members of the task force to give each of the super categories a percentage weighting (i.e. assign % values to categories I, R, D, C, and S so that the toal equals 100%)  As a next step, assign relative weightings within each category.  Using COSTS as an example, assume you have assigned to COSTS a 25% overall weighting:  Take the 8 sub-bullets under COSTS and assign them them relative percentage values that total 100%, and then multiply each of those values by the 25% CATEGORY value to detemine the final overall weighting of the sub-categories.  This still leaves you the task of determining how well each Discovery method meets each of these criteria.  When carrying out the analysis in this manner, disecting a single benefit into many sub-benefits does not end up giving it more weighting in the final quantified evaluation of the trade-offs.
 
Rick, you questioned proposed benefit (I-3).  Certainly, "(I-3) minimizes EMI" is a benefit that many of us would give at least some weighting to.  The fact that one of the benefits of a dc scheme is to minimize EMI should not prejudice us to remove or modify this potential benefit.   I strongly recommend we do not remove or change this category.
 
For R-1 and R-2 you make the comment We need to define "noisy" environment.  I agree with your comment and hope that we have e-mail input proposing how to define those environments.  Ultimately, we each must give a weighting to this benefit and relative scores to each of the discovery methods.  Tests presented will be a substantial help for all of us in making both assessments.  I welcome adding "proposed tests" to the notes on this benefit which may provide useful criteria for making the assessments.
 
For (R-3) you state:  We need further definition on this one.  I agree.  Good definitions are appropriately placed in the notes and will aid in determining the assigned weights.
 
Per your suggestion we can add:
"R-5) Avoids failure to detect a valid powerable device".
"(R-6) Automatic recovery from a cable discharge or ESD event".

Rick, for (D-1) Low risk of equipment damage IF power is ever inappropriately provided 
 
you say How is this an issue of the discovery method, that is not covered above under robustness?

I looked closely at the 4 Robustness items Don proposed, and your 2 additional ones, and fail to see where (D-1) is covered at all by any of them.  Further, D-1, does not appear to be a Robustness Issue.  If anything it is in a different super category of SAFETY.  If we have other safety issues that surface, we could certainly place D-1 there.  In the meantime, I would strongly favor just leaving it where it is.  Again, each of us must decide what the appropriate relative weighting is for this benefit.
For (C-1) you state:  Doesn't this assume a fact that is not yet in evidence?
Are you saying that discovery and load current measurement must use the same method?
I urge all with strong opinions in these areas to present their arguements for and against via e-mail.  These argurements will assist us in determining the weightings to give both to the category, and to how well each Discovery method satisfies this criteria.
 
 
----- Original Message -----
Cc: RDLove
Sent: Monday, September 25, 2000 3:54 PM
Subject: RE: Selection Criteria for choosing a Discovery Method

In general, I agree with your proposal list, and I state my responses below.


(I-2) Minimizes cross-talk interference potential to Gigabit Ethernet and
unidentified future services

I think that the "future" part is kind of nebulous. We should state the requirements that exist now.

Also, I'd rather say does not interfere with 1000BASE-T, rather than minimize.
Otherwise, you could argue that a DC scheme will always minimize interference compared with an AC
scheme. And you would be right.



(I-3) Minimizes EMI

Clearly, only a true "DC" discovery scheme can do this.
Are we then done?



(R-1) Avoids "false positive" detections (quiet and noisy environments)
(R-2) Reliably delivers power to proper PEs (quiet and noisy environments)

We need to define "noisy" environment.
How about passing the EFT (electrical fast transient) test and radiated immunity at 5 volts per meter.
Also, we should use the Campbell clamp fixture to determine where the discovery process fails vs frequency,
as it is stimulated with common mode fields.

Maybe we should add these cables to test: CAT-3, CAT-5, and CAT-6.



(R-3) Avoids giving power to paralleled devices

We need further definition on this one.
No discovery method proposed so far can detect a short paralleled legacy device, depending on it's input configuration.

Also, I would add to the list:
"Avoids failure to detect a valid powerable device".
"Automatic recovery from a cable discharge or ESD event".



(D-1) Low risk of equipment damage IF power is ever inappropriately
provided

How is this an issue of the discovery method, that is not covered above under robustness?



(C-1) Leverages the necessary function of precisely monitoring current
levels to inexpensively perform detection

Doesn't this assume a fact that is not yet in evidence?
Are you saying that discovery and load current measurement must use the same method?
To repeat: Are we then done?


Other survivability tests:
Ability to survive RJ-45 Hipot test, whether DTE power is on or off, and meet the leakage resistance at the end of the test.



comments?
- Rick



    -----Original Message-----
    From:   Donald S. Stewart [SMTP:dsstewart@xxxxxxxxx]
    Sent:   Monday, September 25, 2000 12:25 PM
    To:     802.3af
    Cc:     RDLove; Donald Stewart
    Subject:        Re: Selection Criteria for choosing a Discovery Method


    I applaud Bob's suggestion and his offer to maintain this information. I
    think it will be helpful in reaching a decision. I include below my
    proposals for criteria.
    Regards
    Don Stewart
    ______________________

    Criteria Categories and Specific Elements:

    Non Interfering
    (I-1) Does not interfere with 10/100 Ethernet via cross-talk
    (I-2) Minimizes cross-talk interference potential to Gigabit Ethernet and
    unidentified future services
    (I-3) Minimizes EMI

    Detection Robustness and Flexibility
    (R-1) Avoids "false positive" detections (quiet and noisy environments)
    (R-2) Reliably delivers power to proper PEs (quiet and noisy environments)
    (R-3) Avoids giving power to paralleled devices
    (R-4) Potential for detecting multiple classes of PE

    Avoids Damage to DTE
    (D-1) Low risk of equipment damage IF power is ever inappropriately
    provided

    Efficiency
    (E-1) Ability to deliver maximum, usable power to the PE

    Cost
    (C-1) Leverages the necessary function of precisely monitoring current
    levels to inexpensively perform detection
    (C-2) Amenable to integrating into the PHY
    (C-3) Compact, allowing high density PSE implementations
    (C-4) Compact for PE implementation
    (C-5) Amenable to low cost Mid-span implementations - Env A (including main
    necessary elements: sense over/under current, signature detection, power
    on/off control, on/off switch for current)
    (C-6) Amenable to low cost LAN-switch integrated implementations - Env A
    (including main necessary elements: sense over/under current, signature
    detection, power on/off control, on/off switch for current)
    (C-7) Amenable to Mid-span Env B implementations
    (C-8) Amenable to LAN-switch integrated Env B implementations

    Survivability
    (S-1) Ability to survive ESD
    (S-2) Ability to survive Cable discharge

    --
    Donald (Don) S. Stewart                         Phone: 732-817-5495, FAX x4666
    Avaya Inc.                                      e-mail: dsstewart@xxxxxxxxx
    (former Enterprise Networks Group of Lucent Technologies)
    Cross-Product Architecture                     
    101 Crawfords Corner Road
    Holmdel, NJ 07733