Re: [10GBT-Modeling] RE: [10GBT-Cabling] [10GBASE-T] a channel capacityestimation program for your evaluation
Albert,
Thank you for your input. With the consideration of ANEXT, the Shannon
capacity of CAT-6 is 10Gbps by using the models presented in my program.
Accordingly, your calculation shows the Shannon capacity is 12Gbps. I
admit this is a significant difference. However, even with the 12Gbps
Shannon capacity, there is no way we can achieve 10Gbps effective
throughput over 100m CAT-6 cable if the ANEXT cannot be suppressed by any
meanings.
Regards,
Xiaopeng
Albert Vareljian <albertv@ieee.org>@majordomo.ieee.org on 02/21/2003
01:41:11 PM
Sent by: owner-stds-802-3-10gbt@majordomo.ieee.org
To: xichen@marvell.com
cc: William Jones <wjones@solarflare.com>,
stds-802-3-10GBT-Cabling@ieee.org,
stds-802-3-10GBT-Modeling@ieee.org, stds-802-3-10GBT@ieee.org
Subject: Re: [10GBT-Modeling] RE: [10GBT-Cabling] [10GBASE-T] a channel
capacity estimation program for your evaluation
Xiaopeng,
Just to illustrate how big a potential gap between the measured vs envelope
approach could be, I performed capacity computations based on the Cat6
measured characteristics provided by Terry Cobb.
A 'test' channel was 'assembled' by combining the worst behaving
impairments
out of the set of Cat6 measured characteristics for the Channel
attenuation,
Echo, NEXT and FEXT. The following assumptions were also made: 10 dBm
launch
power with a flat PSD, Echo, NEXT and FEXT cancellation of 40, 25 and 20 dB
respectively, -140 dBm/Hz background.
The capacity without ANEXT came out on the order of 29 Gbps. This was
reduced
to app. 12 Gbps with the ANEXT envelope, as per your code.
As the Channel attenuation and Alien NEXT are the major impairments in the
system, reliable references in a broad frequency range would be the key.
Another source that could have a potential impact on the system, but has
not
been considered yet, is the RF ingress.
Regards,
Albert
xichen@marvell.com wrote:
>Bill,
>
>You are right. Chris did not provide us with the information on alien
>xtalk. And the model used in the program is from a presentation on last
>Nov's meeting. I have given the link of the presentation in the program.
>You can check it out. I understand that this model has not been accepted
>by the SG yet. Since there is no other source of ANEXT model, I decided
to
>use it temporarily. I believe there will be a lot work to be done on
>defining a good model of ANEXT. Once we settle down on this, we will have
>a much more clear picture of what we can do or cannot do.
>
>Also, the model Chris gave is only up to 100MHz (for CAT-5E) and 250MHz
>(for CAT-6). My simple way of extrapolation can be inaccurate. Since
our
>standard has to base on a referable cable model, before we can move ahead,
>we have to work with cable guys to solve this problem.
>
>Regards,
>
>Xiaopeng
>
>
>
>
>
>
>
>
>
>"William Jones" <wjones@solarflare.com> on 02/20/2003 03:47:22 PM
>
>To: <xichen@marvell.com>
>cc: <joseph.chou@realcomtec.com>, <stds-802-3-10GBT-Cabling@ieee.org>,
> <stds-802-3-10GBT-Modeling@ieee.org>, <stds-802-3-10GBT@ieee.org>
>
>Subject: RE: [10GBT-Modeling] RE: [10GBT-Cabling] [10GBASE-T] a channel
> capacity estimation program for your evaluation
>
>
>Xiaopeng
>
>Strictly speaking, Chris provided no information on alien xtalk. Based on
>what he provided yields a capacity of 17.4 Gbps (using your program with
>the aforementioned corrections). Of course alien xtalk can't be ignored
>and must be dealt with accordingly. As a point of clarity, what you
are
>using to model alien xtalk is the pair-to-pair NEXT limit line out of 568b
>lowered by 3dB. We provided the NEXT limit for comparison to our
>measurements only. We can hardly draw any conclusions from the heuristic
>use of a NEXT limit line applied as an alien xtalk limit line.
>
>As to whether scaled measurements will yield capacity results
substantially
>different then the smooth envelop associated with the measurements, I have
>this to say. First, by definition, the envelop exceeds the measurement at
>all frequencies. Therefore, a measurable contribution to capacity will
>occur at every frequency where the measurement does not touch the limit
>line. I suggest reducing the frequency step size of the integration
before
>concluding whether or not there is an appreciable difference in capacity.
>Secondly, from our experience and from talking with a number of
individuals
>who are actively taking cable measurements, high frequency extrapolation
>of these limit lines are rather pessimistic.
>
>regards
>
>Bill
>
>-----Original Message-----
>From: xichen@marvell.com [mailto:xichen@marvell.com]
>Sent: Thursday, February 20, 2003 1:18 PM
>To: William Jones
>Cc: joseph.chou@realcomtec.com; stds-802-3-10GBT-Cabling@ieee.org;
>stds-802-3-10GBT-Modeling@ieee.org
>Subject: RE: [10GBT-Modeling] RE: [10GBT-Cabling] [10GBASE-T] a channel
>capacity estimation program for your evaluation
>
>
>
>Bill,
>
>Sorry I have to clarify my opinions which may not be the same as yours.
>According to the calculation of the program which is based on the ISO
>channel model provided by Chris, the target we are talking about (10Gbps
>over 100m CAT-5E/6 cable) is even theoretically infeasible (channel
>capacity is <10Gbps). And I don't think that there will be an
appreciable
>difference in capacity when the measured data (while scaled to the channel
>model limit) is used.
>
>Another thing I want to clarify is about the Shannon limit. The Shannon
>limit is only theoretically achievable without limit on the complexity of
>system. With the currently proposed approaches (traditional
>modulation/coding schemes), I don't think there is any way for us to make
>it close to the channel capacity. Nevertheless, the implementation
>constraints will only make the really achievable performance worse.
>
>Regards,
>
>Xiaopeng
>
>
>
>
>
>
>"William Jones" <wjones@solarflare.com> on 02/20/2003 11:57:35 AM
>
>To: <xichen@marvell.com>, <joseph.chou@realcomtec.com>
>cc: <stds-802-3-10GBT-Cabling@ieee.org>,
> <stds-802-3-10GBT-Modeling@ieee.org>
>
>
>Subject: RE: [10GBT-Modeling] RE: [10GBT-Cabling] [10GBASE-T] a channel
> capacity estimation program for your evaluation
>
>
>Xiaopeng
>
>I'm glad you feel now that this is only a difficult problem and not one
>that is impossible. We have always said that it was a hard problem. To
>your point that these calculations are theoretical limits that may be
>practically challenging to realize in implementations is precisely why we
>presented cycle based time domain simulation results as well as the
>capacity results. This modeling approach captures the entire effect of
the
>channel and crosstalk including phase information which is lost in the
>frequency domain calculations and which is important for practical
>considerations. These simulations included finite length filters,
>adaptation jitter and clock recovery effects among other things thereby
>accounting for real implementation effects and supporting the
>implementation feasibility.
>
>To the point about the transmit PSD, after correcting for the programming
>errors, I got an additional 760Mbps in capacity with a flat PSD
bandlimited
>to 400MHz. I do agree that alien xtalk is a limiting noise source but
>still dispute the level. If I lower the alien xtalk level by 6 dB
aligning
>it closer with our measured data but still using the ISO cable models I
get
>a capacity of 10.0Gbps on Cat5e.
>
>To Chris' point about using measured data scaled to limit lines, I think
>this is very important. There is an appreciable difference in capacity
>when the calculations are used with smooth curves for the xtalk as
compared
>with actual measured data. There is a lot of physically based structure
>in, for example NEXT, as seen in any of the frequency response curves
which
>is further reflected in the impulse responses. We have seen SNR
>improvements on the order of 3 to 5 dB when using the measurement data as
>opposed to the envelop.
>
>regards,
>
>Bill
>
>William W. Jones, Ph.D.
>Director of Systems Engineering
>SolarFlare Communications, Inc.
>949-581-6830, ext. 2550
>mobile: 619-405-2445
>fax: 949-581-4695
>wjones@solarflare.com
>
>
>-----Original Message-----
>From: xichen@marvell.com [mailto:xichen@marvell.com]
>Sent: Thursday, February 20, 2003 10:23 AM
>To: joseph.chou@realcomtec.com
>Cc: stds-802-3-10GBT-Cabling@ieee.org;
>stds-802-3-10GBT-Modeling@ieee.org; William Jones
>Subject: Re: [10GBT-Modeling] RE: [10GBT-Cabling] [10GBASE-T] a channel
>capacity estimation program for your evaluation
>
>
>
>Joseph,
>
>First, thank you for pointing out the mistake I made on the return loss.
I
>have corrected it in the attached program. As you said, it does not
affect
>the result much.
>
>Also you are correct that the input signal PSD should not be calculated
>using my simplified approach. Instead, the best thing we can do is to
>launch as much as signal power in this band while meeting the FCC
>restriction. However, by my observation, the data I used in the program
is
>very close to the best thing we can do. So you can think the approach is
>reasonably near-optimal.
>
>The difference between Solarflare's data and the ISO 11801 cable models
was
>a topic in the last Jan meeting. Should we follow the standard model or
>some specific measurements is still a problem.
>
>I did not give a careful calculation of the channel capacity based on
>Solarflare's channel model. But I guess you are right. The major factor
>that causes the difference between the results based on the standard
>channel model and Solarflare's model is the strength of the residual alien
>NEXT since it is the dominant noise source. In my view point, suppressing
>alien NEXT is very difficult, especially when there are many disturbers.
>
>Also I would like to emphasize that the calculated Shannon capacity is the
>theoretical limit. It is fairly reliable when the frequency-domain
channel
>model is reliable. However, as all of us have known, it is not easy to
>approach this limit at all. In my opinion, even the Shannon capacity can
>be 14Gbps based on Solarflare's calculation, to achieve effective 10Gbps
>channel throughput will be extremely difficult.
>
>Regards,
>
>Xiaopeng
>Marvell Semiconductor Inc.
>(Please check the updated i3e.m)
>
>
>
>(See attached file: i3e.m)
>
>
>
>
>
>
>"Joseph Chou" <joseph.chou@realcomtec.com>@majordomo.ieee.org on
02/19/2003
>07:28:01 PM
>
>Please respond to <joseph.chou@realcomtec.com>
>
>Sent by: owner-stds-802-3-10gbt-modeling@majordomo.ieee.org
>
>
>To: <xichen@marvell.com>, <stds-802-3-10GBT-Cabling@ieee.org>,
> <stds-802-3-10GBT-Modeling@ieee.org>
>cc: "'William Jones'" <wjones@solarflare.com>
>
>Subject: [10GBT-Modeling] RE: [10GBT-Cabling] [10GBASE-T] a channel
> capacity estimation program for your evaluation
>
>
>
>Hi Xiaopeng,
>
>I am new in this reflector. I looked at your program. Here are some
>observations:
>
>1. The conclusion that you pointed "the Alien NEXT dominates the
>capacity" is surely right.
>2. The Echo (Return loss) used in i3e.m has wrong sign. The return loss
>should be negative (loss) when adding to the signals. However, it does
>not affect the result much.
>3. The Input Signal Si in i3e.m should be calculated based on the
>bandwidth. In the theoretical estimation of channel capacity, the actual
>baud rate due to coding or modulation is not in the picture.
>4. The Alien NEXT model used in i3e.m is about 5 to 10 dB higher than
>the one used by SolarFlare's presentation of last November.
>5. The SolarFlare's presentation also has less Insertion Loss (5 to 10
>dB) than what specified in the ISO 11801 Class D.
>
>The above observations conclude why you and Bill have different result
>of channel capacity: 7GH vs. 14GH for Cat5e cable.
>
>Best Regards,
>
>-Joseph Chou
>
>
>-----Original Message-----
>From: owner-stds-802-3-10gbt-cabling@majordomo.ieee.org
>[mailto:owner-stds-802-3-10gbt-cabling@majordomo.ieee.org] On Behalf Of
>xichen@marvell.com
>Sent: Wednesday, February 19, 2003 2:13 PM
>To: stds-802-3-10GBT-Cabling@ieee.org;
>stds-802-3-10GBT-Modeling@ieee.org; stds-802-3-10gbt@ieee.org
>Cc: William Jones
>Subject: [10GBT-Cabling] [10GBASE-T] a channel capacity estimation
>program for your evaluation
>
>
>
>Hi, Bill and 10GBASE-T SG members,
>
>Sorry for the so late response. I was on a quite long vacation past
>several week.
>
>I have finished a Matlab program to distribute in the 10GBase-T SG for
>the evaluation of the bottomline channel performance. The channel
>simulation is based on the models (return loss, FEXT, NEXT, insertion
>loss) provided by Chris and a presentation (Alien NEXT) last Novermber.
>Without consideration of any implementation and modulation/coding, the
>Shannon channel capacity can be calculated only based on the
>frequency-domain
>channel model. Please read the comments in the program for details
>
>Unfortunately, based on the available channel models, even with a quite
>optimistic belief in the achievable DSP power, the Shannon capacity
>tells me that both CAT-5E and CAT-6 cables cannot support 10Gbps
>throughtput over a distance of 100 meters. Please read the comments in
>the program for details.
>
>Surely, the calculation is completely based on the available channel
>models. I know more work is needed on setting up a channel model
>accepted by all of us. But unless some dramatic improvement can be
>achieved in the alien NEXT suppression, the program tells us pretty much
>the story.
>
>If you have any question about the program itself, you are more than
>welcome to post on the group reflector for discussion.
>
>Best regards,
>
>Xiaopeng
>
>(See attached file: i3e.m)
>
>
>
>
>
>"William Jones" <wjones@solarflare.com>@majordomo.ieee.org on 01/22/2003
>11:18:48 PM
>
>Sent by: owner-stds-802-3-10gbt@majordomo.ieee.org
>
>
>To: <stds-802-3-10gbt@ieee.org>
>cc:
>
>Subject: RE: [10GBASE-T] channel model
>
>
>
>Xiaopeng
>
>How are the calculations coming? Are you using the models Chris sent
>out last week?
>
>regards
>Bill
>
>-----Original Message-----
>From: William Jones
>Sent: Wednesday, January 15, 2003 4:08 PM
>To: stds-802-3-10gbt@ieee.org
>Subject: [10GBASE-T] channel model(part 2)
>
>
>
>Bill,
>
>Sure. Once the common channel model (I only need the frequency domain
>characteristics) is available, I can begin to work on it.
>
>Regards,
>Xiaopeng
>----------
>
>Xiaopeng
>
>Would you be willing to sign up for technical feasibility based on an
>optimal DFE calculation?
>
>regards
>Bill
>-----------
>
>Bill,
>
>I has no problem to use TIA or ISO based channel and noise model once it
>is standardized. My point is that even using the frequency-domain model
>we can still give a quite good estimation of the practically achievable
>distance at a throughtput of 10Gbps over CAT-5E or CAT-6 cables.
>
>Regards,
>
>Xiaopeng
>-------------
>
>Xiaopeng
>
>We believe, as George discussed in his part of the tutorial in Kauai,
>that with an adequate amount of crosstalk cancellation, the throughput
>is achievable. The question then becomes can this level of cancellation
>be practically achieved, hence, my interest in time domain models.
>
>Until we get the models from the channel modeling Ad Hoc, we could argue
>this point endlessly. Until then, I still believe we should not use DSL
>models, but, rather something from TIA 568b or ISO 11801.
>
>regards
>
>Bill
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>