Geoff,
I agree that the MACS in wireless group don’t assume a low-loss, low error rate channel and Ethernet does assume a much better channel. Nonetheless the EPoC
group is looking at a channel model somewhere between wireless and Cat5 and optical fiber.
From the beginning, the input from the MSOs is that they want a PHY that can be adapted to the channel conditions, so considering what wireless groups have
done is instructive. We don’t have to use all of the tools in their toolkit though.
I had originally assumed that we could use a fixed modulation and encoding scheme. Note that the MSOs almost universally use 256-QAM with a fixed FEC digital
video today. However I was informed the intention is to use frequencies above 1GHz which can have severe roll-off in frequency, hence my fixed QAM/FEC assumption was wrong.
My point is that once you open the door to variable modulation/encoding you can create a single PHY that works over a wide range of channel conditions and even
can accommodate both TDD and FDD duplexing.
I am (at least) arguing that the text of the document show a
bias towards a single PHY.
I will quote an IEEE expert who wrote some wise words on the subject of clarity, “I know what I mean, and I am sure that you know what you mean, but
that isn't good enough in the standards business”.
J
Best regards,
Hal
From:
Geoff Thompson [mailto:thompson@xxxxxxxx]
Sent: Tuesday, May 08, 2012 5:36 PM
To: Hal Roberts
Cc: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_EPOC] Latest objectives proposal
Hal-
It should be noted that the MACS used in the wireless groups (e.g. 802.11 and 802.16) DO NOT assume a reliable, low-loss, low error rate transmission channel.
Ethernet (as well as Token Ring, etc) MACs assume going in that the transmission channel works better than open air by orders of magnitude.
Forgive me (as an old baseband bigot) but it seems one of the big issues that we have to come to grips with in this project is just how far we can move the pointer from (for example) sole use of 10BASE5 cable towards an RF environment only marginally better
and more contained than open air; AND when doing this, not destroy the underlying operating assumptions built in over the years for a wired MAC.
Therefore, I get a little uncomfortable when the fact that problems have been solved in the wireless space are referenced here. Problems have been "solved" (to the extent that they have been) in the wireless space precisely because the have greater design
freedom in those groups than does an 802.3 PHY project.
Back in ancient history (before there was an 802.11) 802.3 was approached to take on "wireless". The proposal didn't last long because it would not have been "just another PHY". 802.11 was born and the problem was thrashed out there with the freedom to do
a new MAC.
Best regards,
Geoff
Geoffrey O. Thompson
GraCaSI S.A.
Mountain View, CA 94043
<thompson@xxxxxxxx>
On 85//12 1:35 PM, Hal Roberts wrote:
Marek,
Define “minimal augmentation to MPCP” for me please.
There are plenty of undefined terms in the document, I don’t see why the term “flexibility” has a higher burden than other terms.
We will define flexibility more precisely when we know what the channel models are. If you are still confused what flexibility means it means variable “QAM
constellation density, FEC, guard interval and frame structure”.
We should eliminate the opening for multiple PHYs until someone can show that we can’t do what other standards 802.16e, LTE have done with more difficult channel
model variations.
Hal
From: Marek Hajduczenia [mailto:marek.hajduczenia@xxxxxxxxx]
Sent: Tuesday, May 08, 2012 3:25 PM
To: Hal Roberts; STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_EPOC] Latest objectives proposal
Hal,
Define “enough flexibility” for me, please.
Marek
From: Hal Roberts
[mailto:Hal.Roberts@xxxxxxxxx]
Sent: 08 May 2012 21:21
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_EPOC] Latest objectives proposal
Charaf,
Yes, I have heard the same and would submit the same reasoning I sent out before, “If a single PHY can operate over the wildly varying conditions found in wireless
transmission (i.e. LTE or Wi-Fi with huge swings in signal strength, interference, multipath etc) surely a single PHY should suffice within the more controlled cable environment”.
Obviously the PHY parameters would have to be adjustable, i.e. QAM constellation density, FEC, guard interval and others. This is what is done in LTE and Wi-Fi.
What shouldn’t need to change is subcarrier spacing, symbol duration and other more difficult to change parameters.
As I sent out before, “The burden of proof should be on demonstrating the need for two PHYs.”
Having said all of that, it is much more likely that two PHYs might be considered to work well with TDD vs FDD.
With FDD the downstream would be a continuous signal (with idle patterns when no data is sent) just like DOCSIS which allows easy synchronization to the downlink
and eliminates the need for preambles at the beginning of a burst (i.e. there are no bursts in the downstream). Whereas with TDD we have to define downstream frames and upstream frames along with guard times.
LTE solves this with two types of frame structures, Type 1 for FDD and Type 2 for TDD (see below).
As long as we consider two frame structures as defined under one single PHY then we still need only one PHY.
“The burden of proof should be on demonstrating the need for two PHYs.”
Therefore I would suggest a variation on Gomez’ suggestion:
"Specify one PHY to support subscriber access networks using the EPON protocol and operating on point-‐to-‐multipoint
RF distribution plants comprised of all-‐coaxial cable or hybrid fiber/coaxial media, with enough flexibility to operate both below and above 1GHz and in TDD or FDD duplexing modes."
Thanks,
Hal
From: Charaf HANNA
[mailto:charaf.hanna@xxxxxx]
Sent: Tuesday, May 08, 2012 2:37 PM
To: Hal Roberts; STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_EPOC] Latest objectives proposal
Gentlemen,
From the 5 Criteria discussion, it seems to me the reference to more than 1 PHY has to do with passive versus active coax plants rather than below versus above
1 GHz.
Charaf
From: Hal Roberts
[mailto:Hal.Roberts@xxxxxxxxx]
Sent: Tuesday, May 08, 2012 2:03 PM
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_EPOC] Latest objectives proposal
Kevin,
If a single PHY can operate over the wildly varying conditions found in wireless transmission (i.e. LTE or Wi-Fi with huge swings in signal strength, interference,
multipath etc) surely a single PHY should suffice within the more controlled cable environment.
Hal
From: Noll, Kevin
[mailto:kevin.noll@xxxxxxxxxxx]
Sent: Tuesday, May 08, 2012 1:53 PM
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_EPOC] Latest objectives proposal
There is some concern that operating in the lower bands is significantly different than operating above 1GHz, thus the PHY might need to be different. The reason for "at least
one" is not to have equal and competing specifications, but to allow for two implementations that address multiple sets of coaxial conditions.
If the same goal can be attained by a single configurable PHY, then we would probably be okay with that.
--kan--
From:
"Gomez Chano (LQNA MED)" <Chano.Gomez@xxxxxxxxxx>
To: Kevin Noll <kevin.noll@xxxxxxxxxxx>
Cc: "<STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx>" <STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_EPOC] Latest objectives proposal
Hi,
I did not attend the last conference calls, but I have been following progress through the reflector. I have a question about the wording in Objective 1, which is now
"Specify
at least one PHY to support subscriber access […]"
while previous proposal was:
"Specify a PHY
to support subscriber access networks […] "
Can somebody clarify the rationale for the new wording, which seems to "almost" encourage the group to develop more than one PHY? We have all seen other IEEE groups that quickly
yielded to the temptation of adopting multiple PHYs as soon as they realized that having the group agree on a single PHY was hard work. I would hate to see the same thing happening in EPoC, as this would cause market fragmentation and slow down adoption.
The objective should be "one PHY". Only if the group finds at a later stage a very good reason to develop more than one PHY then that option should be considered.
Just to be clear, for me it would be OK if the PHY for downstream and upstream channels have different parameters. As long as vendors do not have to face the decision of choosing
between multiple and equally valid PHY options when implementing their products, that would still qualify as "one PHY" for me.
Best Regards
Chano Gómez
Lantiq North America
On May 8, 2012, at 9:38 AM, Noll, Kevin wrote:
<epoc_objectives_for_may_2012.pdf>
<="" p="">
<="" p="">