Yair, yet another beautiful side benefit of splitting 4P from Clause 33 – everything you had in Clause 33 will still be there. Link section served us fine there AND allowed your desired application. When we get to 4P PSEs, this problem
goes away. There is zero reason to have a 4P endspan and midspan on the same link SEGMENT as only the midspan link SECTION will be valid (with the midspan required to DC block the endspan from the PD).
The only hole is now the 2P modes of Type 3 PSEs. I am fine to leave this caveat in 33 and not carry it forward to 145 (in fact, I’d prefer it cause I view it as a bastardization of the standard that was SOLELY implemented to violate the
clear intent of AT to deliver 25.5 and only 25.5W to a PD). Mind you, this doesn’t stop you from doing exactly what you did with Clause 33 devices with Clause 145 devices. But there is no reason to overly complicate Clause 145 for this.
Also, piling on with George’s comment. You can’t put active or powered into the definition of link section. What is it when it’s not powered? What do we probe to detect, CC and class?
Tech Lead, Cisco Systems
Chair, IEEE P802.3bt 4PPoE Task Force
From: Yair Darshan <YDarshan@xxxxxxxxxxxxx>
Reply-To: Yair Darshan <YDarshan@xxxxxxxxxxxxx>
Date: Monday, May 15, 2017 at 5:48 PM
To: 4PPOE Reflector <STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_4PPOE] Link section vs "channel" and link segment
- The 1st problem that I see with link-section definition is that it doesn’t allow PSE alternative A and PSE alternative B to be connected to single
PD. It says single PSE to single PD.
- I understand your point but per the current definition for link section, It looks that Midspam and Endspant can’t be connected to A PD while the intent
is to allow it as it was before. There are parts in the spec that take care of such case to prevent issues.
- Link segment can resolve issue (2) or changing the definition of a link section.
- Better definition for link section is required to fix issue (1).
- Because of the above I believe that all the ~45 comments from Geoff to change all
“link section” create more issues than we had before.
From: George Zimmerman [mailto:george@xxxxxxxxxxxxxxxxxxxx]
Sent: Monday, May 15, 2017 10:28 PM
Subject: Re: [802.3_4PPOE] Link section vs "channel" and link segment
The use of the qualifier 'active' is a real problem. The definition of what is a links section and what is not, should not change it up on the status of the device specified in the state diagram. The links section
is the links section is the links section at all stages of the state diagram. If we use the word Active in the definition, then somewhere in the middle of the state diagram the piece of cable becomes the links section. That's just weird and wrong.
George A. Zimmerman, Ph.D.
Experts in PHYsical Layer Communications
This all has me wondering what active means...
Does active mean both PSEs are powered but only one is "active". Note Dual-sig PDs will present a detection signature on both modes.
Or does active mean powered?
The word active can be deliberately manipulated to mean whatever a vendor wants it to mean.
(GOT) I was under the impression that 802.3bt allows you to gang one active endspan PSE (Alt A) plus one active midspan PSE (Alt
B) simultaneously to get additional power.
^^^ this is a really bad idea, the IEEE should have nothing to do this type of system
On Wed, May 10, 2017 at 3:37 PM, Geoff Thompson <thompson@xxxxxxxx> wrote:
I have copied your questions below
(and corrected some spelling and typographical items)
1. I undestand that the term "channel" is ANSI/TIA term for the channel model with 4 connectors as defined in D2.4 page 211.
Why it is not in the list above?
(GOT) Because we write our standards for the international market with an eye towards eventual adoption by ISI/IEC. That means we use international rather than national or
regional standards for reference whenever possible. In this particular case the definition in the ISO/IEC standard is technically equivalent to the TIA definition so there is no need to cite both.
2. Does your plan is to change also the usage of "channel" and "permanent link" in clause 145.4.9 ?
(GOT) In a word, yes, but it is a little more complicated in my view. First, the problem with figure 145-38 is that it is a cabling standard diagram and only (costly) correct
in that context. Thus we face two choices (a) to acknowledge it as a stolen cabling drawing (and somewhat incorrect in our context) or (b) to edit it into correctness. To do that we would have to do the following: (a) redepict (at least) the end connectors
from a single box with one "c" into two boxes (i.e. a mated pair) then (b) move the endpoint demarcation lines to align to the mating interface of the mated pair and (c) change the term "channel" to "link section".
"permanent link" should be changed to "link segment" (not "link section")
3. Currently Midspans operated per the definitions of 145.4.9. How your 45 comments to change "channel" to "link segment" will affect it?
(GOT) My changes should fix the technical errors introduced by doing that. We can still use the terms cross connect and interconnect without a problem (but I feel that they are unnecessary).
1. What is the link section model (how many connectors, cordage? cable?)
2. What is the link segment model (how many connectors, cordage? cable?)
(GOT) It doesn't matter. The tradition in 802.3 (which is an equipment specification group, not a cabling group) has been to specify the media from MDI to MDI (or in the case of PoE from PI
to PI) by overall performance of the link segment/section. How a cabling standard chooses to divide that up inside their standard and between cables and cabling hardware is outside our scope.
3. Why you prefer to use terms (link segment/Link section) from ISO/IEC and not from ANSI/TIA
(GOT) See answer #1 for slide 2 above.
1. I understand that this definition allows Switch without PoE and Midspan to be connected to the same PD correct?
2. I understand that this definition doesn't allow Endspan and Midspan to be connected to the same PD, correct?
3. Regarding (2), what if one of the PSEs (Endspan or Midspans is not active), does it meets the definition above? I am asking because we have equipment that work like this for backup purposes.
4. What is your opinion regarding to modify the the definition above to
"Link section: The point-to-point medium connection between two and only two
Power Interfaces (PIs).
(GOT) I think your addition to my definition improves the definition. It may need more work or a clarifying note to cover the case during the contention process while the PSE PI to be used when
the system goes active is being chosen.
Yair: I like the current one since it is more flexible. It allows me to support my current equipment while the above doesnt allow....which is my main problem unless you modify your fantasy definition to the one
that I have suggested in the previous slide.
(GOT) The current one is not correct. That is because the "scope" of generic cabling does not include the "application specific connector" (i.e. the RJ-45 that is at each end of the "generic
The transmission path between any two interfaces of generic cabling. (From ISO/IEC 11801.)
As I said above, I like your modification. We will probably need to discuss this a little more in the meeting.
1. where from IEEE802.3AF/AT?
(GOT) Again, perhaps we should add the word "active" to the slide. Otherwise, this is a trick question. You know the answer much more intimately than I do.
Why it is more complex? This case is covered by IEEE802.3AF/AT and 802.3bt.. (Backoff time etc. It means that there is only one PSE active.
(GOT) I was under the impression that 802.3bt allows you to gang one active endspan PSE (Alt A) plus one active midspan PSE (Alt B) simultaneously to get additional power. In that case, if we
say that there is one and only link section it has (at least) a funny shape.
1. You can't prevent such a case from happening, it can be by mistake and most likely will not work over 4-pairs due to serious unbalance issues (It will fail PSE_Vdiff, Icon-2P_unb, Overload etc.)
(GOT) This is not a question.
2. If only one PSE is active, that there is no issues at all. Correct?
3. I prefer using link segment instead of link section. What is your strongest argument against this proposal.
(GOT) Link segment and link section are exactly equivalent in the case of an endspan PSE.
We invented the term "link section" during the development of 802.3af to be able to have a term for the power path when it was not the same length as the data path (i.e. for the midspan case). We made the decision
at the time that the term "link section" was defined to have it apply to either the endspan case or the midspan case. We COULD have decided at that time to only make the new term apply to the midspan case but that is not the decision we made at that time.
That is not a decision that we can revisit at this point.
I hope this answers your questions. My guess is that to go any further on theses issues we need to discuss it during the meeting rather than by correspondence. I look forward to seeing you in New Orleans.
You have submitted many comments regarding replacing “channel” with “link
I have read your presentation and I have some questions and some concerns.
I would like to start a discussion with you about this much before the next meeting and I am attaching your presentation with questions/comment inline.
I’ll appreciate if you can address them.
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<Thompson_01_0317_with Yair comments.pdf>
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