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:
Additional requirements that there would be a strong push to add some other
"features":
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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