Hi Geoff
Thanks for the reply.
Yes, I understand that it is no law issue.
When I use "legal" I meant conformance to the relevant standards.
According to your last conclusion, I
understand that splitting 4 pair cable to 2 outlets (each outlet gets 2 pairs) is
valid scenario which PoEp has to address too.
Now we will have the following PD options:
High Power 4P PD
Or two High Power 2P PD's
Or two IEEE802.3af PDs
Do we really want detect and power all
options or we wish to detect and power only 4P or 2P high power or single IEEE802.3af
PD and only prevent damage to two IEEE802.3af PDs connected to the same cable and
leave the decision if to power it or not to the system (implementation specific
etc?).
Yair
From: Geoff Thompson [mailto:gthompso@xxxxxxxxxx]
Sent: Tuesday, June 07, 2005 6:56
AM
To: Yair Darshan
Cc: Geoff
Thompson; STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: RE: [8023-POEP] 2P v 4P
and safety [Unscannable attachment] [Unscannable attachment]
Yair-
"legal" vs. common...
There is no matter of law involved, only conformance with voluntary standards.
If you insert a splitter into a single outlet then there is no conformance
issue.
If you split a cable to 2 outlets you are not conformant with TIA-568. The US has always
"required" that you run a single 4-pair cable to each RJ-45.
The International Standard, ISO/IEC 11801 does not require this. It was an
international fight of long standing. The German national body and a major
international connector manufacturer (US headquartered) bitterly opposed
mandating 4 pair per outlet. Therefore, 2 pair is allowed.
I hope this helps.
Geoff
At 02:46 AM 6/5/2005 , Yair
Darshan wrote:
Hi Geoff an all,
Are all the examples you have shown of using the same cable for two outlets are
"legal" within the IEEE802.3?
I guess that if it is not "legal" but people are doing it any way, we
have only to make sure that damage will not be caused but we don t have to support
and detect those cases?
Yair
From:
owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of Geoff
Thompson
Sent: Saturday, June 04, 2005 2:24
AM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-POEP] 2P v 4P
and safety [Unscannable attachment]
Steve-
It is not at all uncommon, particularly in older installations, to have a
single 4-pair cable run to a box with 2 outlets. The idea being that you could
serve 2 applications (e.g. telephone, 10 Mbps, 100 Mbps) with a single cable.
Connector manufacturers also sell a breakout adapter to do the same thing, i.e.
bring out the pairs from a single RJ-45 to each of two RJ-45s with the correct
pinouts for 10/100 Mbps Ethernet.
In the scenario that you describe, someone could could plug a breakout adapter
into an outlet that had one of the following:
1) 2 separate
10/100 Ethernet connections in a single 4-pair sheath, each connection of which
had a conventional 2P 802.3af PoE (or PoE Plus) provision. This would be used
to connect to 2 different 10/100 2P PDs.
2) A single
10/100 Ethernet connection with 4P PoE Plus. This would be used to connect to a
single 10/100 2P PD and an additional 2P PD that has no data connection.
I hope this helps.
Geoff
At 10:04 AM 6/3/2005 , Steve Robbins
wrote:
Wael and all,
In regard to the question, should a 4P PSE = 2 independent 2P
PSEs, I got an interesting question from someone a couple of days ago,
suggesting an application I hadn't thought of.
Basically, the guy was asking the following: Suppose
you had a 4P PSE. Could he make some sort of passive splitter that would
allow him to power two independent 2P PDs? It sounded like the splitter
he was thinking of was just some RJ45 connectors and some wire. He told
me there is already some similar gadget on the market (from Siemon?) that
allows data to be split somehow, and he was wondering if power could also be
split.
Of course I told him I didn't know the answer to that,
because a 4P PSE hasn't been defined yet. But obviously, if you combine
an endspan 802.3af PSE with a midspan 802.3af PSE, then you have a system you
could split easily.
I don't know what the specific application is, or if anyone
else would be interested in this. But it might be something to think
about in the 2P vs 4P debate.
The main problem with defining 4P=2x(2P) is that it basically
forces the PD to have two separate PD controller circuits, and two separate
DC/DC converters. This increases the cost of the PD, which
understandably, the group is loathe to do.
But the alternative (using diodes in the PD to passively
combine the power from all 4 pairs, into a single DC/DC converter) is messy
too. As Clay Stanford from Linear Tech showed in his presentation at the Austin meeting, you'd
have to actively balance the currents at the PSE end. Otherwise, small
differences in wire resistances and/or diode drops could lead to big
pair-to-pair current imbalances. So it appears this approach makes the
PSE significantly more complex and costly, which the group is also loathe to
do.
The lack of an attractive 4P solution is the main incentive
for considering high-current on 2P. But then of course you get into other
issues.
That's basically where the debate stands right now, with no
clear answers yet, although most people have an opinion.
Steve Robbins
-----Original
Message-----
From: owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx]On
Behalf Of Wael Diab (wdiab)
Sent: Friday, June 03, 2005 5:03 AM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-POEP] 2P v 4P and safety
Hi
Steve, Yair, Chad and all,
Ive been trying to catch up on this thread, which brings up many good points.
One thing that I am not sure we have exhausted yet is Steve's original point #6
(repeated below for convinience so that you dont have to scroll through the
entire thread).
I dont understand why that would be more complex than just picking one. Today,
in .af, the PD has to accept power on either pair. Increasing power via a 2P
scheme would be similar, with hopefully enhancements to the classification to
differentiate it from leacy 2P power. Additionally, the PD may have the option
to be in yet a higher power class and draw power over all 4P. In that case we
would have to address the balancing issues that were touched on (but we would
have to do that anyway if we went with 4P regardless).
So we have PSEs that can support a higher power mode over 2P and others that
can go further and support even more power over 4P. In my mind these could
address different needs in the market and I would hate to have to just pick
between one power point and the other unless I really have to.
As an aside, I think the questions of whether or not 4P = 2x(2P) and how much
power can be drawn over 2P max and 4P are both good ones, but I would be
interested in anwering these first before pre-empting which scheme we go with
and/or whether we allow both options in the standard.
here is the original point so that you dont have to scroll all the way down
6.
Suppose PoE Plus allows both 2P and 4P. How do we define this without getting
into several
different types of PSE and PD, with all the complexity
of hooking them together? I think the
answer is simple: We define a 2P system, and
then say that it's legal to have one or two of these
on the same cable. So, two independent 2P
systems make a 4P system. I think this is really the
only way to go, but of course I'm open to other ideas.
wael
From: owner-stds-802-3-poep@xxxxxxxx on behalf of Yair Darshan
Sent: Fri 6/3/2005 1:22 AM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-POEP] 2P v 4P and safety
Hi Steve and all,
I absolutely agree with you that the complexity difference
between 2P and 4P are narrow due too the other problems that we have with 2P
higher current.
It is worth to check the advantages of detecting broken wires
compared to other alternatives in order to decide what alternative is good
enough and keep
reasonable cost and reliability for the most popular installations.
Yair
From: owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx]
On Behalf Of Steve Robbins
Sent: Thursday, June 02, 2005 9:23 PM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-POEP] 2P v 4P and safety
I totally agree that we need help from the cable group to determine more
realistic current limits.
When I started this email chain, I was looking for some way
to decide between 2P and 4P on the basis of complexity and cost. Everyone
knows that 4P is more expensive, because it requires more circuitry to switch
and current-limit the extra pairs. But I realized that a 2P system might
need extra circuitry too, if it was pushing the current closer to safe
limits. (That's how the safety issue got included.) So the
complexity/cost gap between 2P and 4P is narrowed by this argument.
That's the main point I was trying to make.
But now I see all this discussion has led to another big
point: Worst-case analysis is greatly simplified if we have circuitry that
detects broken wires, because then we only have to consider one case, where all
wires are carrying nearly equal currents. Without detection, broken wires
just makes a mess of any worst-case analysis. Basically, where do you
stop? How many broken wires are reasonable? Unfortunately, I don't
think "one" is a reasonable answer because if a cable suffers damage
sufficient to cut one wire, there could very well be two cut. There
appears to be a large number of possibilities and I don't see any good way to
trim it down to a manageable few, unless we rule them all out by making the
silicon a little smarter.
-----Original
Message-----
From: owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx]On
Behalf Of Chad Jones
(cmjones)
Sent: Wednesday, June 01, 2005 8:16 PM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-POEP] 2P v 4P and safety
Time to throw into this conversation:
What I read in this email chain is that we need to limit the
current on the PAIR to the limit of one conductor, presently quoted as
420mA. I'm going to guess that only incrementally raising the current
from 350mA to 420mA and raising the min voltage to something like 51V is going
to cause a decent number of present participants to drop out. This is
only 21.4W at the PSE for two pair (and 42.8W for 4P). It will certainly
cool my interest in the project. I will also reiterate stated goal of
pushing the physical limits of the cable.
We definitely need help from the cable group with this
project. One of the questions I have is how they derived the 420mA
number. Does it change if we only use 2P in a 4P cable? Also, does
it change if only 1 wire in a pair is carrying current (like when one conductor
breaks)? How much margin is built in (in other words do we have use their
number as the max or do we also add margin on top of it)?
Last comment, I would not be opposed to mandating current
balance monitoring within a pair and between the pairs for PDs that need the
high power modes that could cause this 'safety hazard'.
- Chad Jones
From: owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx]
On Behalf Of Yair Darshan
Sent: Wednesday, June 01, 2005 4:04 AM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-POEP] 2P v 4P and safety
Hi
Steve and all,
I
basically agree with you regarding the situation you have described.
(One wire broken==>Current is doubled ==> temperature rise increased
==> cable and/or connector parameters may be impaired==>
we need to sense this situation and protect the infrastructure).
Actually
we are protecting the infrastructure in the IEEE802.3af by limiting the
current, time and duty cycle. However, we are not sensing a broken wire in
order to protect from doubling the current from the simple reason that it is
not needed IF the time duration peak current and duty cycle of the event kept
low enough so increase in temperature rise will not happen. The numbers of the
IEEE802.3af were chosen in order to ensure this behavior (there are additional
reasons for the numbers that we have decided in the IEEE802.3af and the end
result was integration of all argument to get reliable operation while keeping
the cost of silicon down)
I
guess that we should aim to the same concept in our new project i.e. set the
numbers that in case of failure keep the infrastructure parameters in their
operation range without additional sensing and features in order to keep the
system simple and low cost.
Probably we will need to revisit the protection mechanism by optionally adding
a sense function that will alert of broken wire due higher current in 2P concept
compared to the IEEE802.3; however we need test results in order to decide the
way to go and some of us working on getting lab data.
Other
comments:
1. PD
has to have IEEE defined components (PHY or others) otherwise it is not a
compliant PD. PD is a powered DTE. DTE is a device defined by IEEE802.3. Hence
PD must meet IEEE802.3. We don't care about other implementations that are
using PoE technology and are not IEEE802.3 compatible.
2. You
are right that a link is not required at the first place; actually according to
the spec PSE operations are independent of data link status (33.2.4) however
the spec allows wide flexibility for specify implementation specific errors
under the variable "error_condition" which will results by power shut
off.
In other words if A PSE vendor/ System designer decides that the PSE sees
something that is not normal (he decides what is normal or not; he is the
vendor and he should know.) and it is not specifically covered by the spec,
(there are many scenarios that meets that definition) it can be considered
"error_condition" as specified by the state diagram.
According
to the above, if during operation system reports to PSE that "something
bad has happen" (by getting information that data was good and now is dead
and current is higher than normal for example) PSE is encouraged to do
something about it.
3. I
agree with the statement that true worst-case conditions in a 2P system must
assume one wire is broken. In 4P, if we stay around the AF currents that we
don't have to take in consideration that we have problem if one wire was broken
due to the fact that this condition was tested and we don't have problems with
it. If in 4P we will have higher current than 350mA than we have to test again.
Yair
From: owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx]
On Behalf Of Steve Robbins
Sent: Wednesday, June 01, 2005 4:12 AM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-POEP] 2P v 4P and safety
Yair and all,
Perhaps I could make this a bit clearer. Here is a
hypothetical situation: Suppose we determine that CAT5 cable can carry
800mA per twisted-pair (400mA per conductor), and under worst-case conditions
(max amb temp, big bundle, etc.) the wire temp stays 10C below the point where the
cheapest insulation starts to soften. So we set I_CUT to 810mA, and it
seems safe.
Now suppose that we have actual worst-case conditions
somewhere, but then one wire breaks. The whole 800mA is flowing through
one wire, not two. The wire resistance is doubled, so power dissipation
in the twisted-pair doubles, and the temp rise increases. (I'm not sure
that the temp rise would double, since the power dissipation in the other pairs
hasn't increased. But obviously the wire carrying 800mA will get hotter,
probably significantly hotter.) If it goes up 11C, it exceeds the softening
point.
True, the Ethernet data would be messed up, but who
cares? A PD doesn't even need to have a phy chip. Loss of link is
not a reason for the PSE to shut off power, at least under 802.3af, because
link is not required in the first place. In the above example the load
current stays below I_CUT, so power stays on and the wire temp stays above the
softening point until eventually something bad happens.
The point is, true worst-case conditions in a 2P system must
assume one wire is broken. In a 4P system, I think we'd have to assume
one wire was broken in each of the pairs. (Don't assume broken wires are
statistically independant events. If a wire breaks there is a good reason,
and other adjacent wires could very well be broken too. Once, when I was
at Boeing I had a whole bundle of wires come loose in my hand when I gave it a
small tug. They all broke off right at the connector pins. Yet
every individual connector contact in that bundle had survived a much stronger
pull test right after crimping. A lengthy failure investigation
determined someone had used an improperly calibrated crimp tool, which made the
wire brittle and eventually led to fatigue. After two years in the field,
some were actually broken but still just barely touching, which led to
intermittent equipment failures.) < br>
Steve
-----Original Message-----
From: Yair Darshan
[mailto:YairD@xxxxxxxxxxxxxx]
Sent: Tuesday, May 31, 2005 1:03 AM
To: Steve Robbins;
STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: RE: [8023-POEP] 2P v 4P and safety
Hi Steve and all,
Please find attached below few comments on the
thoughts presented below:
1. There are basically two roadblocks to higher power:
a. The limited amount of current that can be carried on a single wire
(not a pair of wires).
We must assume that sometimes
a wire will break, or a connector pin will go bad,
so all the current will be on
one wire instead of a pair. This fault condition must define
the limit on how high I_CUT
can go, for safety.
b. The affects of heating and current imbalance on the
magnetics.
----------------
1a. If a wire or a pin will break the data path
will not work due to the fact that the magnetic will immediately saturate.(Lets
assume that at the worst case all pairs are data pairs such in 1G)
There
fore assuming the above condition may not be considered as a worst case that we
have to handle since it is a case that the system is not working and we don't
care what happens as long as we are not causing damage.
Regarding causing damage:
If
one conductor is break, we will have twice the current going through the other
conductor and if we keep the TLIM/TOVLD and duty cycle than even for 2-4 times
the current overload/Ilim numbers we probably will not have damage issue due to
the averaging factor over time.
Connector pin according to its spec need to meet 750mA at 60C. With cables it is a
temperature rise issue which is not an issue for the overload/ILIM timings and
duty cycle.
Regarding safety issue: There is no safety issue
here in terms of human safety. There is an issue of "Infrastructure safety
or equipment safety" in terms of damage however as mentioned above, with
TLIM/TOVLD and duty cycle limitation the equipment is kept un damaged and
"safe".
1b. Yes, this is one of the major issues in 2P.
--------------
2. To make sure we get it right in terms of safety, I propose:
a. The objective regarding the goal of higher power should be amended to
include
a few words about safety.
b. Let's look for a worst-case scenario to keep in
mind while we work on the standard.
The best one I've thought of
so far is the airline industry. Assume PoE is used onboard
a jet so that passengers can
surf the net or watch DVDs in flight, without the batteries
in their laptops dying.
How hot do you think the FAA will allow the wires to get? How
much current can a single
conductor (in a bundle) carry before it reaches that temp?
-------
2a - We don't have a mandate to define safety
(human safety) in our standard. We need to address
the reader to current safety standard.
We should address issues that have
impact on keeping the equipment and infrastructure undamaged.
2b - I agree that we should look for the worst case HOWEVER the worst case
scenarios should be real cases and not corner or theoretical cases in order not
to increase the cost of solution or eliminating some implementation or support
some applications.
Regarding the example presented: I guess that it is not the worst case since in
aircraft designs there are a lot of margin in the design (Aircraft...) so in my
opinion it is not representing the worst case.
--------
3.
I thought about Clays presentation a lot over the weekend. It seems to me
that reaching
higher power (>30W) will require two things:
a. Current imbalance sensing to detect broken wires,
so we can increase I_CUT beyond
what a single conductor can
handle, without compromising safety.
b. Active current balancing to keep the magnetics
happy. Although this won't solve the
heating problem.
------
3a. The intent is not clear. Do you mean current
balance in 4P? If this is the case than Yes, we need to address this issue
and your suggestions sounds reasonable.
3b-
Active and passive current balancing to the magnetic was discussed in the AF
and we didn't want to force this requirements in the standard due to the
following reasons:
-
The vendor should keep his system working under
his equipment spec. How he does it is implementation specific.
- Forcing a requirement for active/passive current balancing will
increase the port cost while in most cases it is not required (above some
cabling length there is no issue)
Actually
we address this issue in the informative part of the standard and let the
designer to decide how to handle the worst case situation.
In our new project doing active current balancing
will dramatically increase the port cost so the the 2P concept will cost much
higher that the 4P... In addition as you have mentioned, the heat issue still
exist.
Bottom line: In my opinion: Current balancing is
not cost effective
--------
5. Compare the complexity of a 2P and a 4P system that carry equal
power. The 2P system
would need about twice the current per conductor as the 4P system. So,
while the current on
4P system might just be low enough to avoid the need
for ACB/CIS, the 2P system would almost
certainly need these features. So the complexity
difference between 2P and 4P may not be as
big as previously thought, at least in some medium
power range. For much higher power, 4P
would require ACB/CIS as well, but 2P becomes
infeasible because of safety.
---
5. Agree. From complexity wise, the is no
difference between 2P and 4P high power and in my opinion 4P from system point
of view will cost less than 2P and will be more reliable by far.
(Regarding safety: again there is no safety issue here (the system may not
work... but no safety issue))
----
6. Suppose PoE Plus allows both 2P and 4P. How do we define this
without getting into several
different types of PSE and PD, with all the complexity of hooking them
together? I think the
answer is simple: We define a 2P system, and
then say that it's legal to have one or two of these
on the same cable. So, two independent 2P
systems make a 4P system. I think this is really the
only way to go, but of course I'm open to other ideas.
-----
6. Basically I agree with this concept which is
what the 4P concept (part of it) represents: Let's take two improved AF power
channels, combined them together to have twice or more the power by having the
4P..
The
problem that I have with part of your suggestion is that it will allow at the
PSE side, PSE that supports only 2P high power and PSE's that support only 4P
which leads to the undesired environments were we have many different PSE's and
PD's that will cause us complex system.
I suggest looking at the 4P as the only HP
concept that will address all PD types.
By
using this approach, the 4P design will be efficient, and simple.
And when it will be integrated, the difference in chip level between 4P and 2P
will be small enough to stay cost effective.
From system point of view (cost, reliability, flexibility etc) 4P will
represents better cost numbers than 2P.
Yair
From: owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx]
On Behalf Of Steve Robbins
Sent: Monday, May 23, 2005 7:50 PM
To: STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Subject: [8023-POEP] 2P v 4P and safety
PoE Plus Team,
Here are some thought I had over the weekend regarding 2P vs. 4P, and
safety. I checked with Mike, and he wrote that it's okay to post this on
the reflector and get a converstation going.
1. There are basically two roadblocks to higher power:
a. The limited amount of current that can be carried on a single wire
(not a pair of wires).
We must assume that sometimes
a wire will break, or a connector pin will go bad,
so all the current will be on
one wire instead of a pair. This fault condition must define
the limit on how high I_CUT
can go, for safety.
b. The affects of heating and current imbalance on the
magnetics.
2. To make sure we get it right in terms of safety, I propose:
a. The objective regarding the goal of higher power should be amended to
include
a few words about safety.
b. Let's look for a worst-case scenario to keep in
mind while we work on the standard.
The best one I've thought of
so far is the airline industry. Assume PoE is used onboard
a jet so that passengers can
surf the net or watch DVDs in flight, without the batteries
in their laptops dying.
How hot do you think the FAA will allow the wires to get? How
much current can a single
conductor (in a bundle) carry before it reaches that temp?
3. I thought about Clays presentation a lot over the weekend. It
seems to me that reaching
higher power (>30W) will require two things:
a. Current imbalance sensing to detect broken wires,
so we can increase I_CUT beyond
what a single conductor can
handle, without compromising safety.
b. Active current balancing to keep the magnetics
happy. Although this won't solve the
heating problem.
4. Maybe it's time for an acronym here. How about Active Current
Balance (ACB) and Current Imbalance
Sensing (CIS). They seem to go together, so "ACB/CIS"?
5. Compare the complexity of a 2P and a 4P system that carry equal
power. The 2P system
would need about twice the current per conductor as the 4P system. So,
while the current on
4P system might just be low enough to avoid the need
for ACB/CIS, the 2P system would almost
certainly need these features. So the complexity
difference between 2P and 4P may not be as
big as previously thought, at least in some medium
power range. For much higher power, 4P
would require ACB/CIS as well, but 2P becomes
infeasable because of safety.
6. Suppose PoE Plus allows both 2P and 4P. How do we define this
without getting into several
different types of PSE and PD, with all the complexity of hooking them
together? I think the
answer is simple: We define a 2P system, and then
say that it's legal to have one or two of these
on the same cable. So, two independant 2P
systems make a 4P system. I think this is really the
only way to go, but of course I'm open to other ideas.
Steve Robbins