Re: [802.3EEESG] 10BASE-T question
Joseph-
Thank you for your reply.
I believe that the two of us have achieved my goal, specifically that a
low power Cat5 10BASE-T PHY may well be a significant part of the
solution.
At the very least, it warrants a thorough investigation as opposed to
superficial dismissal.
I look forward to discussion of this topic at our meetings.
About Cat3. Alan Flatman who is quite an expert in both the international
premises cabling standard and twisted pair deployment throughout the
world will be in Ottawa. We should consult him on the market penetration
effect of limiting EEE to Cat5 or better.
Best regards,
Geoff
At 11:20 AM 4/4/2007 , Joseph Chou wrote:
Geoff,
Your points are well taken. Following please find my comments:
==============è
However, even though we modify the
standard to allow lower output voltage for 10BaseT, we probably will end
up a 10BaseT phy which has comparable power consumption of
100BaseT.
No, the idea would be that with revised specs AND new designs based on
contemporary supply voltages the power comsumption would be (a) lower
than 100BASE-Tx and (b) the power consumption of the 10 Meg would be
significantly lower when it was in IDL that when it was transmitting
data.
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# According to my impression
(though I will try to collect more measurement data), 10BaseT, even
though operates at 2V p2p (instead of 5V p2p), consumes similar power to
100BaseT during full traffic. However, I do agree that with design tricks
the 10BaseT at IDL can save quite some power on line driver. I will post
some data later on.
==============è
It will lose the advantage of
speed change. The benefit of changing the spec could turn out to have a
new lower power 10BaseT when it drives longest CAT 3 cable thus only
10Mbps can be negotiated successfully.
No. Pat's proposal was to drop Cat3 compatibility and design the new one
around Cat5 cable. Cable that was worse than Cat3 (AT&T DIW) was the
design point for 10BASE-T. Cat5 is significantly better than Cat3 or DIW
in every way and there is very little true Cat3 left these days. Nobody
has installed in new installs for years. In particular, 10BASE-T has
enough drive to drive about 180 meters of Cat5 cable. If we made no other
change than to cut the drive level back to that required for 100 meters
we should be able to save quite a bit of power. They are other tricks we
could do for additional power saving once we have the design open. The
rules would be that it has to be backward compatible with existing
10BASE-T over Cat5 at up to 100 meters.
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# Dropping CAT3 compatibility
could cause a problem that the EEE compatible PHY can not work on area
with existing CAT3 installation. It may be true that US or western world
do not have much CAT3 left. However, for ROW, there are still demands on
10BaseT over CAT3 office.
# Attached you may find a diagram showing the waveform which is a
template test (Fig 14.9) using 100m CAT5 cable with reduced transmit
voltage of 10BaseT (2V p2p). It is very possible that the template needs
to be modified too (not just scaled). Apparently, the fat bit de-emphasis
does affect the shape of waveform. Of course, this is only one data
point.
# In summary,
l
10BaseT with reduced
voltage also reduces power.
l
10BaseT with reduced
voltage may have comparable power with 100BaseT under full traffic. (will
post more measurements later)
l
10BaseT with reduced
voltage under IDL may achieve lowest power. (to be quantified
later)
l
Section 14.3.1 need to
modify to allow the change of voltage, test model, and template of
10BaseT
l
Changing the voltage and
test cable model (CAT3 to CAT5) may cause backward compatibility issue -
EEE compatible PHYs can not work on area with existing CAT3 installation.
This issue has to be solved.
l
The 0BaserT or
electrical idle may start from the concept of IDL of 10BaseT with
information exchanged in the modified link pulse.
==============è
This has sufficient promise to be worth
investigation. (electrical idle)
It is however, non-trivial.
The requirements, as I see them, would be:
- Maintain
link integrity state information
- Not
interfere with PoE probe pulse
- Support
the code transfer requirements of Auto-Negotiation
- Meet the
bandwidth requirements for keeping the DSP parameters current in the
higher speed PHYs
- Probably
needs to have some sort of baud width compatibility with current
PHYs
- Be
enough lower power to be worth doing
Additional requirements that there would be a strong push to add some
other "features":
- Rapid
link integrity response time, sufficiently improved to support fast
switch-over to a redundant link.
- Reliable
and speed consistent mechanism for far-end fault detection
-
Combining the 2 items above
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# The RPS with
electrical idle can no longer be hidden seamlessly in existing PHY
interface characteristics. A new PHY EEE compatible PHY- will be
inevitably required. I agree that the effort is non-trivial.
Best Regards,
-Joseph
-----Original Message-----
From: Pat Thaler
[mailto:pthaler@BROADCOM.COM]
Sent: Wednesday, March 28, 2007 6:37 PM
To: STDS-802-3-EEE@listserv.ieee.org
Subject: Re: [802.3EEESG] 10BASE-T question
Mike,
I think that some adjustment to the 10BASE-T transmit voltage would be
entirely appropriate.
The 10BASE-T output voltage spec (IEEE 802.3-2005 14.3.1.2.1) currently
requires that the driver produce a peak differential voltage of 2.2 to
2.8 V into a 100 Ohm resistive load - a very normal output voltage when
the standard was written in the late 80's, but pretty high nearly 20
years later. This voltage allowed 10BASE-T to coexist in bundled Cat 3
cable with analog phone ringers. The transient when an analog phone
ringer goes off-line in that situation could produce over 250 mV.
That high output voltage is not necessary over Cat 5 or better
cable.
The simple change would be to add a differential output voltage spec for
operation over Cat 5 or better cable. In that case, remove the minimum
voltage spec for peak differential voltage into a 100 Ohm resistive load.
One still would keep the maximum voltage spec of 2.8 V or perhaps
substitute a lower maximum. Change the requirement for the Figure 14-9
output voltage template to be the signal produced at the end of a
worst-case Cat 5 cable instead of at the end of the (Cat 3) twisted-pair
model.
This should be fully backwards compatible with existing 10BASE-T
compliant PHYs over Cat 5 cable. The newly specified transmitters will
produce a signal over Cat 5 cable that is within the range of signal that
the original 10BASE-T produces over the Cat 3 cable channel it specified.
That template provides a minimum eye opening of 550 mV. If I plugged the
numbers into my calculator correctly, the attenuation difference between
Cat 5 and Cat 3 cable at 10 MHz is more than 4 dB so this should allow
the transmit voltage to drop by that. It should be very little work to do
this change.
A more aggressive change that would require real work would be to
determine what receive voltage could be tolerated by today's receivers
which probably can tolerate a smaller eye-opening especially if they are
a 1000BASE-T receiver operating in a slowed down mode. But in that case,
one would either need to only use the lower eye-opening when stepped down
by EEE or add negotiation for low voltage 10BASE-T to auto-neg because it
wouldn't ensure backwards compatiblity with classic 10BASE-T
receivers.
I think the fully-backwards compatible change would be pretty easy to
justify. To summarize, for operation over the channels specified by
100BASE-TX, 1000BASE-T and 10GBASE-T, delete the spec for minimum voltage
into a 100 Ohm load and change the test condition for the Figure 14-9
voltage template to be over a worst case 100BASE-TX channel.
Regards,
Pat
At 01:46 PM 3/28/2007 , Mike Bennett wrote:
>Folks,
>
>For those of you who were able to attend the March meeting, you may
>recall we had a discussion on 10BASE-T (in the context of having a
low
>energy state mode) and what we might change to specify this, which
>included possibly changing the output voltage. Concern was
raised that
>the work required to specify a new output voltage for 10BASE-T would
>far outweigh the benefit. Additionally, there was a question
regarding
>the use of 100BASE-TX instead of doing anything with 10BASE-T.
Would
>someone please explain just how much work it would be to change
>10BASE-T and what the benefit would be compared to using 10BASE-T
with
>the originally specified voltage or 100BASE-TX for a low energy
(aka
"0BASE-T" or "sleep") state?
>
>Thanks,
>
>Mike