From: Joseph Chou [mailto:joseph.chou@REALCOMTEC.COM]
Sent: Wednesday, April 04, 2007 11:21 AM
To: STDS-802-3-EEE@listserv.ieee.org
Subject: Re: [802.3EEESG] 10BASE-T question
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.
ç=============
# 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.
ç=============
# 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":
ç=============
# 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