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
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