Second, the waveform captured below doesn't appear to be a 10BASE-T waveform. Any 10BASE-T signal that transiitioned from low to high at 0 ns would transition back to low at either 50 ns or 100 ns, but that picture shows a part of the trace that continues high past the second transition time for a pulse that is wider than 100 ns. Except for start of idle (which shouldn't be used in the template), the Manchester signalling in 10BASE-T never has a pulse wider than 100 ns. Once that trace is removed, it appears that the waveform shape may have fit within the template if it was scale to an appropriate voltage instead of attempting to just skim the top of the first transition part of the template. The voltage shown in that picture is too low.
Regards,
Pat
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:
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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.
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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.
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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