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FYI -------- Mensaje original --------
Peter ? I thank you for your
diligence.
I have been considering these issues, and find as
some of these arguments overreaching.
Particularly the ‘future proof’ discussion for the
home network market.
I would note first that the most prevalent home
networking technologies are not even considered in the
presentations from September (a hybrid of wired BASE-T
Ethernet and advanced 802.11 wireless ? and yes, I know that
in some markets these have been argued as unavailable by
construction and regulation, but the presentation
environment was not limited by those considerations).
What I see are market
justifications that don’t necessarily get linked to
objectives.
For example, if future proofing were to be considered
as important to enabling this market, the objectives should
make some provision for an
autonegotiation protocol (at
least an optional one) ? to build a base for that future. I will have to leave the
optical testing issues to your analysis.
Coming from the copper world, when we have simulation
models they are fairly detailed, and call out each of the
residual impairments, using widely known and demonstrated
techniques for cancellation. I don’t get that same feeling
from the analysis I have seen in the record of
presentations. I have been reviewing the detail of the
presentations but get the impression that they are
predominantly using a linearized model on a channel known
for nonlinearities.
While some reference in the documents is made to
signal processing for removing nonlinearities, the required
accuracy and the performance limitations of those in the
target environments is neither well known nor tracked in
multi-vendor presentations.
I am not saying it cannot be done ? just that
technical feasibility and noise components for this channel
need to be better shown before they live up to the ‘effects
are well known and understood’ criteria for technical
feasibility.
Hopefully these will be addressed in the tutorial in
November. George
Zimmerman Principal,
CME Consulting Experts
in Advanced PHYsical Communications Technology george@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx 310-920-3860 (PLEASE
NOTE NEW EMAIL ADDRESS.
THE OTHER WILL STILL WORK, BUT PLEASE USE THIS FOR
CME BUSINESS) From:
Peter Stassar [mailto:Peter.Stassar@xxxxxxxxxx]
Hi
Bob, Thanks
for your email response sent about 3 weeks ago. I
would like to start to re-emphasize that my main concern was
in the end of the email which I sent on 22 July: “In
conclusion I have not been convinced that 1Gb/s Ethernet
over 50m of worst case POF is technically feasible and
even more that an installed POF link can be upgraded to
higher speeds, which I believe is necessary to justify
long lifetimes of home-installed POF networks.” As
you suggested I took a close look to the presentations to
the meeting in Ottawa, 4 weeks ago. Before
commenting to those I will first address the 5 points from
your email. I inserted comments in “red”
in
the thread below. So
back to the September presentations. In
Eugene_GEPOF_01_0914 I see a strong claim that POF is future
proof and that it is superior to existing technologies like
twisted pair, coax and power line. This presentation also
says “Tomorrow SMART HOME needs future proof networking
medium”, which is a statement which I fully support and, I
believe, have always clearly stated. This is however also
the weak point of all presentations which I have seen so
far. I continuously fail to find any evidence that POF and
the 1GbE technology to work with it, is sufficiently future
proof. In Tsukamoto_GEPOF_02_0914 the following is said
“Customers may use the network over 30 to 50 years. Is GbE
enough in such a far future?”. This is exactly the point I
tried to make during the CFI consensus building meeting in
Beijing and during the San Diego meeting. It’s my strong
belief that 1 Gb/s is NOT sufficiently high speed to justify
deployment of POF in the home. Some references have been
made to shorter wavelength windows of POF which could
provide lower attenuation than at 650nm. Having looked at
the Ottawa presentations I see some inconsistencies. While
in Eugene_GEPOF_01_0914 I see a claim that in the range 450
to 580 nm the attenuation will be lower than at 650 nm, I
conclude from Tsukamoto_GEPOF_01b_0914 that the POF standard
is only specified for the 650nm window and that therefore
operation is other wavelength windows is not specified and
thus not guaranteed. A lower attenuation in the range 450 ?
580nm would indeed be great, but what will be the bandwidth
of POF in that wavelength range? It is not trivial that it
will be the same or better or worse. I am under the
impression that POF is a kind of multimode fiber and
bandwidth is strongly dependent on the wavelength. In
conclusion, having looked in detail at the presentations to
the Ottawa meeting and the clarifications in your email, I
am still of the opinion that insufficient evidence has been
provided that the proposed solutions are capable of
multi-vendor interoperability (capability of developing a
multi-vendor interoperable transceiver design from the
specification under worst case conditions) and that the POF
medium is sufficiently future-proof (or in other words
upgradeable to speeds well in excess of 1Gb/s) to justify
installations in the home for many decades to come. Kind
regards, Peter
Stassar,
施笪安
Technical
Director,
技术总监
Huawei Technologies Ltd,
华为技术有限公司 European Research Center,
欧洲研究所 Karspeldreef 4, 1101CJ Amsterdam The
Netherlands Tel:
+31 20 4300 832 Mob:
+31 6 21146286 From:
ROBERT GROW [mailto:bobgrow@xxxxxxx]
Peter: Thank you for documenting your
concerns following the July plenary meeting. We reviewed
your concerns during our interim Study Group meeting, and I
offer some general response. I believe these thoughts are
consistent with the consensus of the GEPOF SG. Detailed
responses to your specific points will likely follow from me
and others. A few general points: 1. We have certainly noted your
acknowledgement that you are satisfied with POF
applicability for two of the three markets our participants
want to address (i.e., automotive and industrial). Study
Group members though did express some confusion because many
of the presentations you choose to comment about were
clearly only addressing requirements for the automotive
market. Please see September presentations for additional
support for the application to home networking. Peter: I just
looked at the available documentation. I understood that
many were addressing the 15m automotive market. 2. In response to your repeated
comment “15m (typical?)”, yes 15 meters is the requirement
for automobiles. That is reflected in one of our link
length objectives for 15 meters with four in-line
connections. If you look, you will see similar 15 meter
objectives for p802.3bp and p802.3bw. Peter: I do understand the 15m
objective. I only put some questions marks on the
testing done on 15m links. In the optics world a
laboratory test on a TYPICAL fiber is completely
different from a test on a worst case fiber under worst
case operating conditions. Worst case conditions have a
big impact on maximum loss and (I assume for POF) also
on bandwidth. Therefore optics people are generally not
convinced by a laboratory test on just 15 km of typical
fiber. What kind of margins are available, etc. 3. You also frequently commented on
the lack of detail on modulation techniques. We apologize
for that, your question would have been answered if you had
been able to attend SG meetings. In defense of
SG presenters, please understand that most of our
participants helped develop a VDE specification for
operation at up to and including 1 Gb/s with link lengths
consistent with our automotive and home reach objectives.
Consequently, much is assumed to be a given with those
folk, and it is perhaps excusable that presenters did not
have an outside reader trying to understand everything from
only the presentation in mind when preparing the
presentation. Peter: I am of the opinion that
details on how to actually “do it” needs to be provided
by presentations and not via verbal clarifications. I
understand that often things are a given for a limited
group of people, but I also think you are very much
aware that in 802.3 one needs to convince 75% of the
plenary and not only the “insiders”. There are implementations of the VDE
specification from multiple vendors. All tests that used a
PHY used one of these implementations. If you look at
September presentations, you will see that additional
presentations on testing include detailed
one slide summaries of the characteristics of the VDE PHY. Peter: Thanks for pointing this out.
It would be great to see some evidence of those
different implementations and interworking testing. I am
under the impression that all test results shown at the
September meeting (Lichtenegger_GEPOF_0914 and
perezaranda_GEPOF_01_0914) were from the same PHY
vendor and not between PHYs from different vendors. So
it would have been very interesting to see results from
interoperability testing between devices from different
vendors. 4. You also repeatedly commented that
simulation was not sufficient for justification of technical
feasibility. While you are entitled to that opinion, but
give no rationale why simulation is not valid for
demonstration of technical feasibility, I would point out
that we have approved projects in the past based on
simulation (in my personal experience as far back as
1000BASE-T). Please also note that simulation is listed in
IEEE 802 rules as an acceptable evidence of technical
feasibility. As is true for most engineers, the
participants in our SG find it useful to look to both
simulation and lab testing and when possible implementation
tests expecting consistency. As noted in my point 3, many
of the test presentations you critiqued used an existence
proof of technical feasibility ? an implementation of the
VDE specifications tested at 1000 Mb/s. We do not only
relay on simulation as some previous 802.3 projects have. Peter: regarding to your statement
“While you are entitled to that opinion, but give no
rationale why simulation is not valid for demonstration
of technical feasibility, I would point out that we have
approved projects in the past based on simulation (in my
personal experience as far back as 1000BASE-T)”, I would
like to point out that for optical PHYs many years of
(bad) experience have taught most optical engineers that
simulations in the optical field in most cases need to
be confirmed by experiments in order to judge the
accuracy of the simulations. That’s why I (and probably
not only myself) keep repeating that to demonstrate
technical feasibility of Optical PHYs results from
simulations are generally not sufficient. 5. You also repeated in your comments
a question about worst case channel. Please note that the
environmental requirements for automotive applications have
higher temperature, greater EMC, and specific connector
requirements. Industrial applications similarly will also
have higher temperature than home, and greater EMC
challenges. While vibration effects on optical power is
important for the automotive channel, it is not considered
relevant to the channel for nome networking, so our
participants have looked at the effects of vibration on
optical power, and consequently the automotive channel will
include losses for vibration. With our three major markets
asking for a standard POF solution, and different objectives
that address those markets, it is appropriate for a
presentation to focus only on one particular market
application, and unfailr for you to criticize those
presentations for not also covering the home network
application. Peter: on the topic of worst case
channel I am NOT referring the range of environmental
characteristics, despite the fact that they do play a
significant role. I am referring to an optical link
model with worst case characteristics appropriate for a
distance of at least 50m. A test with a spool of 50m of
typical POF is generally not regarded as testing a link
under worst case conditions. I am under the impression
that in many in-force optical specification in 802.3 a
lot of work has been done on defining a worst case
channel. This generally is defined such that it will
support manufacturers in designing, manufacturing and
testing transceivers. Performing a test on a spool of
50m POF is indeed proof of concept, but by far not
enough to claim complete technical feasibility, or in
other words sufficient maturity of the technology that
it actually can be manufactured in high volume and with
a high yield, work on worst case links of 50m POF in the
home in a multi-vendor environment. I am afraid that
this has not yet been demonstrated. The fiber shown on
page 16 of perezaranda_GEPOF_01_0914 had an attenuation
of 0.19 dB/m, but according to page 5 of
Tsukamoto_GEPOF_01b_0914.pdf, IEC 60793-2-40 category
A4a.2 has a maximum loss of 0.4 dB/m. What was the
bandwidth of the test fiber and how does that relate to
the worst case specification? Furthermore it was not my intent to
criticize those presentations not covering the home
market. If I came across to criticize them then I
apologize for that. I was just putting remarks to those
presentations what they were aimed at and what they were
not aimed at. Please see September and upcoming
November presentations for additional support of feasibility
for home networking. ―Bob |