Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: Feliz Haridad


Sorry about the tone of my last reply. I'll try to tone it down :-)

Patrick Gilliland wrote:
> >Increasing transmitter power in an unconstrained manner for
> >a multi-level system which modulates the intensity of the
> >laser to correct only for SNR lost at the transmitter would
> >saturate the receiver. This is not a good thing for a MAS
> >system. This would result in an optical compression penalty
> >and would likely INCREASE rather than DECREASE SNR,
> >specifically for the highest intensity level at the receiver.
> >My PAM5x4 proposal is independent of laser wavelength.
> An increase of transmitter power to the levels I have
> referenced would saturate a present day GbE 1300nm
> receiver.  However, most receivers employ some form of
> AGC which can address the problem of saturation.
> The biggest issue in increasing the maximum power levels
> would be the need to extend the dynamic range of the
> receiver to accomodate any additional transmitter power.

For a multi-level system, The AGC would have to be linear and capable of
maintaining equal effective BER's for all levels. In general, this requires a
far more sophisticated AGC than is commonly employed in binary signaled systems.

A carefully designed multi-level system would establish and maintain an optimum
dynamic range at the receiver by accurately controlling the current applied to
the laser for each level. 

> ----------------------------------------------------------------
> >You have a right to your opinions and your own proposals as I do mine.
> >My MAS proposal is based on 5 levels (PAM5x4). I do not advocate using
> >10 levels for MAS just as you wouldn't advocate using 2600 nm lasers
> >(i.e. 2 times 1300 nm). Please don't add to the confusion. My PAM5x4
> >is a complete 10 GbE PHY proposal with all interfaces, coding, O/E
> >support, etc. defined. Unless you're going to propose a 10 level PAM
> >system, please drop this idea to keep this MAS thread on track.
> I believe you have advocated a PAM9 system in the past.  I
> am referring to page 72 of your own presentation entitled
> "Multi-Level Analog Signaling Techniques for 10 Gigabit Ethernet"
> which was presented to the IEEE 802.3 committee.
> In this paper you emphasize the reduction to a 3dB link penalty
> for a PAM9 system which yields 3bits/baud with a transmission
> rate of 3.33 Gbaud.  You also conclude with the statement,
> "The technology to go beyond PAM5 is here now".  So I must
> assume your position has changed somewhat in the intervening
> weeks and months.

Page 15 of the same tutorial discusses alternate modulation techniques such as
Optical QAM. My Kauai technology update further discusses alternatives past
PAM5. See page 24 of

> This is in contrast with your statement above which implies the
> proposal is complete and will not be amended or evolved.


You are grossly misinterpreting my intentions. My PAM5x4 proposal is a complete
proposal. Most aspects of the proposal would have to change to support PAM10.
I've submitted close to a hundred proposals related to gigabit link
architectures to the IEEE 802.3 or NCITS T11 committees in the past decade and
am ALWAYS open to constructive criticism. P802.3ae is free to accept all, part
or none of the proposal and amend and evolve it at will.

I simply said that I would not support 10 level PAM knowing what I know about
PAM, laser noise, SNR, alternate modulation technologies, etc. If you would like
to propose PAM10, please feel free to use my proposal as a template. In the
absence of a counter proposal from you or a third party on PAM10, the issue will
go nowhere. Based on your previous notes, you are 100% against MAS. Given this
position, you won't run with the idea. That's why I asked you to drop it. I
apologize if I ruffled your feathers with this remark. I'm just trying to make
forward progress with MAS.  

> At a certain point, if PAM5 or PAM9 or PAMX is adopted by the IEEE
> committee, it will no longer be personal to you.  In fact, the
> present debate is not solely about your proposal which you have
> chosen to make public.

As I said, go right ahead propose PAM9 or PAM10 if you like. I don't see any
debate. I won't support PAM10 at this time.
> This reflector is also an open forum for the interchange of ideas
> and for the debate of various technical and associated issues.
> It is not within your purview to decide who shall be allowed to
> comment on the merits of PAM5 versus PAM9 or PAMX.  I therefore
> respectfully decline your invitation to remain quiet when I have
> something relevant to share with the members of this forum.

I didn't ask you to be quiet nor would it do any good :-) I merely expressed my
view of your suggestion. 

> ---------------------------------------------------------------------
> >It is clear in the MAS proposal as well as this thread, that the MAS
> >Signaling rate is 5 GBaud, not 1.25 Gbaud. This means that I'm sending
> >a symbol 5,000,0000,000 times per second.
> Again, directly from page 17 of your paper referenced above,
> "5 GBaud = 2.5 GHz enables the use of low cost CMOS"
> which is an apparent contradiction of your recent statements
> to the effect the real MAS transmitter bandwidth for your
> 5 Gbaud PAM5 system will need to be ~ 5.5GHz.  In the same
> proposal you are championing the cause of bandwidth reduction.
> If there is some confusion it may arise from these two apparently
> inconsistent arguments.

One more time with gusto :-)

2.5 GHz is the fastest effective symbol rate and corresponds to 5 GBaud.
Look at is this way: The 1000BASE-X signaling rate is 1.25 Gbaud. The coding is
8B/10B. The highest effective frequency is generated by the 101010... pattern
and is equivalent to 1/2 the baud. Therefore, the maximum effective 1000BASE-X
signaling rate is 625 MHz. The same general rule applies to PAM5x4 making the
highest effective frequency 2.5 GHz. This has NOTHING to do with bandwidth of
the laser, driver, receiver, TIA, rise time, etc.

5.5 GHz is the proposed laser bandwidth using the formula ~1.1x Baud. Laser,
driver and rise/fall times are all considered in this number. Compare this to
the corresponding required laser bandwidth for a 12.5 Gbaud serial system. The
answer is ~13.75 GHz to transport 10 Gbps of Ethernet data.
Where again is the confusion and inconsistency?

> ------------------------------------------------------------------
> >The symbol sent is a 5 level symbol containing approximately 2.3 bits.
> >4 of these PAM5 symbols are used to represent one byte. The overhead
> >of 2.3 x 4 = 9.22 - 8 = 1.22 bits is used to transport a Forward
> >Error Correcting (FEC) code which is used to increase effective SNR
> >at the receiver. I call the code PAM5x4, per the customary labeling
> >of a code to represent the encoding of one byte of MAC data.
> Actually, 2.32 x 4 = 9.28 - 8 = 1.28 is closer.  At the risk of
> creating semantic contrast, the 1.28 bits is the FEC burden
> for an entire byte for a PAM5 code according to your proposal.

9.22 is the correct number. I did say "approximately 2.3". 1.22 bits per PAM5x4
symbol is the overhead allocated to FEC, special symbols, transition density
guarantees and "thrown away" as invalid codes. See page 10 of

> I have seen numerous postings which indicate 8B/10B encoding will
> be supported.  I understand from reading your proposal and by
> assuming you have calculated the bit rate correctly, the 8B/10B
> might be used at the MAC, XMII, etc. but would be stripped away
> in the transceiver and replaced with Viterbi or Reed-Solomon code.
> If this is not the case, there would be a penalty imposed due to
> supporting the 8B/10B encoding in addition to Viterbi or Reed-
> Solomon which would reduce the information bandwidth another 20%.

My PAM5x4 proposal supports Hari and strips away the 8B/10B code. 

> ----------------------------------------------------------
> >> I do not agree that MAS and laser safety are independent for
> >> the case of the 850nm lasers I cited in my previous posting
> >> which I have left in below.
> >
> >I believe that you'll need to make a better case for a dependency
> >because I blew your previous case out of the water above.
> Referring once again to your paper, on page 37 you acknowledge
> the advantage 1310nm lasers have in a higher Class 1 safety
> limit.  This limit is ~6mW for 1310nm while the limit for 850nm
> is ~ 400uW.  If this advantage you claim for the 1310nm lasers
> higher Class 1 limit is not relevant to the MAS proposal for
> other wavelengths such as 850nm, it probably should not be listed
> as an advantage.  It appears your opinion has changed.
> I agree with your original conclusion stated in your white paper;
> the higher Class 1 safety limit creates an additional degree of
> freedom for 1310nm transmitter design.  One of the design choices
> may be to overcome the SNR penalty due to MAS with additional
> transmit power rather than to rely solely upon the benefits of
> FEC.  Of course, any increases in transmit power must be rational
> with respect to the overall system design.

I agree with all you say. But what does it have to do with your original comment
of a dependency between MAS and laser safety? Once again, MAS is a signaling
method and is independent of laser wavelength and transmit power. 

> ----------------------------------------------------------------
> >
> >The pictures above are YOURS not MINE!!! You show no alternative other
> >than Hari as a MAC interface.
> Of course the pictures I sent in my last posting were mine.
> I thought your pictures were very helpful, so I returned the
> favor.  It may be HARI is best suited as a MAC interface.

It sounds like we finally agree on something. One small correction: Your picture
showed Hari being a MAC/PHY interface. I incorrectly called Hari a MAC
interface, I meant to say MAC/PHY in agreement with your picture.

> ----------------------------------------------------------------
> >
> >Please follow the developments of the 10 GbE HSSG. Most HSSG proposals
> >to date which include the very high-speed SerDes/EnDec that you show
> >are associated only with a specific PMD type, Serial, and are
> >considered to be part of the PMD. PMD is NOT synonymous with
> >transceiver module. A Serial PMD may include a Hari interface,
> >high speed mux/demux/CDR, and a transceiver module.
> New ideas are always coming along.  Some may follow the exact
> course set by predecessors, others may deviate.  This is the way
> of progress.  May the best ideas win.
> The issue of how to partition the PMD is an open question until
> decided by a vote.   I happen to agree we should not use the terms
> PMD and transceiver synonomously.  It maintains what I consider
> the proper perspective on the separate nature of the transceiver
> from the CDR, SERDES, and possible HARI functions.

Holy cow! Two agreements in one day!

> --------------------------------------------------------
> 1) Inclusion of HARI increases the jitter budget by your
>    logic above because it increases the number of elements
>    over the conventional serial approach.

You are incorrect. Hari has its own jitter budget which is separate from the
PMD-medium-PMD jitter budget. A link architecture employing Hari is
significantly different than a conventional link architecture such as GbE or 1/2
Gbps Fibre channel.

> 2) Part of reducing the losses in high speed serial transmission
>    involves reduction of radiative losses by providing continuous
>    ground planes around transmission lines.  This also produces
>    a beneficial effect in EMI reductions.  Improving control of
>    transmission line impedance reduces reflections and has a
>    similar  EMI benefit due to the reduction in peak voltages.


>    Keep in mind HARI reduces the transmission bandwidth by four,
>    but it also multiplies the number of transmission lines by a
>    factor of four.  So while the EMI peaks have been reduced in
>    frequency, they have the potential to be greatly increased in
>    amplitude.

Yes. But a 10-12.5 Gbps trace won't work on FR-4, CMOS, and for trace distances
required in 10 GbE products. We've been through this in previous notes. Also the
EMI on a 16 line + clock 622 MHz parallel interface would be greatly increase in
amplitude compared to Hari by your logic.
> 3) A 10Gbit serializer/deserializer could be implemented any number
>    of ways.  The choices of technology are well established in this
>    thread, but they include CMOS/SiGe, GaAs, SiGe, etc.

Yes, but not economically. There's that darn Economic Feasibility PAR Critter
I'm trying to address. My personal belief is this this is the most important but
elusive critter.
> 4) The traditional serial approach has the advantage here over
>    a HARI approach because of the removal of the MAS encode/decode
>    logic at the serial output.  This conclusion is consistent with
>    your logic in (1) above.


> Best Wishes to all for the New Year,
> Patrick Gilliland
> patgil@xxxxxxxxxxx


Merry Christmas and Happy New Millennium,

Richard Taborek Sr.         Tel: 408-330-0488 or 408-370-9233       
Chief Technology Officer                   Cell: 408-832-3957
nSerial Corporation             Email: rtaborek@xxxxxxxxxxxxx  
2500-5 Augustine Dr.           Alt email: rtaborek@xxxxxxxxxx 
Santa Clara, CA 95054