Re: [802.3_EPOC] short term ad hoc committee on mulitple modulation profiles until January interim
Hal,
A good set of questions, indeed.
I have a few of my own, that did not get any time to be asked on the last
call.
- First, I think that looking at 50+ million modems and drawing
conclusions based on such data is a mistake from the get go. Statistically,
we will have much smaller service groups than 50 million modems and we
should be observing behavior per node, and variations in such behavior,
rather than averaging everything. The law of large numbers is there for a
reason ? in here, we should be looking at trees, and not at the forest.
- Second, I find it hard to reconcile data presented on the call
yesterday with data shown by Ed from BHN at the last meeting. To me, it
seems that either both operators have completely different network designs,
use different equipment, or perhaps the measurement methodology is
different. While one data set supports clearly multiple profiles, the other
one puts that observation into question. Do we then follow the larger data
set just because it is larger?
- Third, in the SNR distribution per node shown on the yesterday?s
call, it seems that two profiles would cut it for a grand majority of the
connected modems. The question then becomes: how distant are these modems
from the node itself? Is there any correlation between distance to node and
observed SNR or it is rather a complex function of cable, passives and any
other sources of noise? Furthermore, are all modems connected to the given
node exactly the same? We assume all modems are alike, but I think it is
only fair to assume they are not, and under the very same conditions may
behave slightly different, especially in terms of measured SNR values (seems
that some discussions yesterday support this conclusion).
- Fourth, and perhaps last for now. What is the premium (in
relative terms, % wise if you like, taking a single profile equipment as a
base value of 1.00) acceptable for equipment supporting multiple profiles
versus single profile equipment? There is no free lunch as we all know and
making devices more complex entails extra cost due to hardware and
management complexity. I am trying to understand where the pain threshold is
located and when it becomes simpler for the network operator to go and fix
the coax problems rather than trying to address them through the use of
super-intelligent and highly-adaptable equipment. Recall that Ethernet is
first and foremost about simplicity and robustness, while adaptiveness and
tons of options (and knobs to fine tune such options) does not sound very
Ethernet-like to me.
Regards
Marek
From: Hal Roberts [mailto:Hal.Roberts@xxxxxxxxx]
Sent: Wednesday, December 05, 2012 17:46
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_EPOC] short term ad hoc committee on mulitple modulation
profiles until January interim
All,
Some observations based on Dave Urban?s presentation of downstream SNR field
data. The purpose is to check if: A) I?ve understood the data properly and
B) to see if there are some points we have consensus on (recognizing we only
got partway through the presentation):
1. Impact of Analog Optics: It is often stated that the data we
should be analyzing should subtract the impact of the analog optics, since
this will not be present in some EPoC scenarios. Observation: The impact
of the analog optics is negligible. The optics sets a baseline of about 42dB
SNR for digital channels. However the problematic channels have noise that
is 10dB worse than the optical baseline. Eliminating the optical noise will
only improve the SNR of a 30dB modem by a fraction of a decibel. Therefore
elimination of the analog optics will not substantially alter the problem or
solution space. The higher SNR channels will, however, improve by
elimination of the analog optics.
2. Source of Low SNR Modems: These are generally correlated to modems
with low received signal power (RSSI) due to long in-home cable runs or high
split ratios. Observation: However this leads to the following mystery when
examining the Gateway Data??..
3. Gateway Data - Impact of Locating Modem at Home Entry Point:
Locating the modem here would seem to solve both low signal problems as well
as reduce in-home ingress. Surprisingly, locating the modem here has a
relatively negligible affect with only a 2dB shift in average SNR and a ½ dB
reduced Standard Deviation. Observation: How do we reconcile #2 and #3?
4. General Conclusion: The only potential way of eliminating the low
SNR outliers is to reduce those modems experiencing a low signal
(eliminating the analog optics will not do it). Therefore, locating the CNU
at the entrance to the home where the signal level should be close to 0dBmV
(and any in-home ingress at lower levels) would seem to be the way to do
this. However, current data shows this is not the case. The only
possibilities to explain this seem to be: A) Low signal is not the cause of
low SNR or B) the ?gateway? location mysteriously still experiences low
signal strength even though it is not behind a long cable run or high loss
splitters.
Do I have the observations correct?
It would be interesting to see the SNR of the ?gateway? located modems
paired to received signal levels to get a correlation between low SNR and
low RSSI.
Hal
From: Salinger, Jorge [mailto:Jorge_Salinger@xxxxxxxxxxxxxxxxx]
Sent: Monday, December 03, 2012 7:40 AM
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_EPOC] short term ad hoc committee on mulitple modulation
profiles until January interim
Dear IEEE P802.3bn members,
Expanding on Mark's Email, attached below, during the last IEEE EPoC F2F
meeting we had a lot of discussion regarding multiple modulation and coding
schemes (M-MCS) for EPoC. However, the time available was not sufficient to
express all views an opinions, both pros and cons. Given the interest in the
topic, and the desire to make a decision on whether to use M-MCS or not for
EPoC rather soon, there was consensus on creating a short-lived ad-hoc for
the purpose of discussing the potential benefits and draw-backs of M-MCS in
EPoC. To that end, this ad-hoc will be a forum to discuss the merits and
draw-backs of M-MCS for EPoC, and to try to arrive to a recommendation on
whether M-MCS should be used or not in EPoC for the next EPoC F2F meeting.
While we may discuss approaches for implementing M-MCS for EPoC to
facilitate the discussion on its merits or draw-backs, it is not the purpose
of this ad-hoc to arrive to a recommendation on how M-MCS would be
implemented even if it is deemed appropriate to use it.
To that end, and after considering multiple options for timeslots for this
meeting, we will hold an initial discussion tomorrow, Tuesday, at 9:30 AM
ET. I tried to pick this timeslot with 2 criteria in mind: a. that the
meeting not overlap with existing EPoC or DOCSIS 3.1 activities, and b. that
it be possible for the widest range of participants as possible. I think
that the a. criteria is met with this timeslot, but it is very difficult to
pick a timeslot that meets the b. criteria for everyone (in particular, I
know that this timeslot is pretty early in the West coast).
During this initial meeting we will review objectives and then start with a
presentation on the benefits of M-MCS based on data collected by Comcast.
Subsequent meetings will include additional presentations on the benefits of
M-MCS, and presentations on the draw-backs of M-MCS and/or complications
from its implementation.
Please see a meeting invitation following this Email. Please let me know
should you not receive that meeting invitation.
Thanks!
Jorge
From: Mark Laubach <laubach@xxxxxxxxxxxx>
Reply-To: Mark Laubach <laubach@xxxxxxxxxxxx>
Date: Monday, November 19, 2012 6:26 PM
To: EPoC Task Force <STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx>
Subject: [802.3_EPOC] short term ad hoc committee on mulitple modulation
profiles until January interim
Dear IEEE P802.3bn members,
At the meeting last week, it was mutually desired by everyone to have more
discussion time on the topic of multiple modulation profiles as there was
not enough time at the meeting for everyone to fully share their views.
The following ad hoc is charted until the January P802.3bn interim meeting
in Phoenix, AZ:
Name: Multiple Modulation Profiles
Chair: Jorge Salinger
Until: January 2013 P802.3bn Interim meeting
Focus: facilitate discussion and information sharing on multiple modulation
profiles
For everyone having a holiday this week, please have a happy one!
Cheers,
Mark Laubach, Chair
IEEE P802.3bn EPoC PHY Task Force
Broadband Communications Group
Broadcom Corporation
1351 Redwood Way
Petaluma, CA, 94954
Description: broadcom.jpg
Tel: +1.707.792.9093
Cell: +1.650.996.2219
_____
From: Mark Laubach <laubach@xxxxxxxxxxxx>
Reply-To: Mark Laubach <laubach@xxxxxxxxxxxx>
Date: Monday, November 19, 2012 6:26 PM
To: EPoC Task Force <STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx>
Subject: [802.3_EPOC] short term ad hoc committee on mulitple modulation
profiles until January interim
Dear IEEE P802.3bn members,
At the meeting last week, it was mutually desired by everyone to have more
discussion time on the topic of multiple modulation profiles as there was
not enough time at the meeting for everyone to fully share their views.
The following ad hoc is charted until the January P802.3bn interim meeting
in Phoenix, AZ:
Name: Multiple Modulation Profiles
Chair: Jorge Salinger
Until: January 2013 P802.3bn Interim meeting
Focus: facilitate discussion and information sharing on multiple modulation
profiles
For everyone having a holiday this week, please have a happy one!
Cheers,
Mark Laubach, Chair
IEEE P802.3bn EPoC PHY Task Force
Broadband Communications Group
Broadcom Corporation
1351 Redwood Way
Petaluma, CA, 94954
Description: broadcom.jpg
Tel: +1.707.792.9093
Cell: +1.650.996.2219
_____
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_____
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_____
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