RE: 10 Gbit Ethernet PMD
Gentlemen,
I would highly recommend reading the material available on the web presented
at a variety of IEEE meetings. See:
http://grouper.ieee.org/groups/802/3/10G_study/public/index.html
jonathan
> -----Original Message-----
> From: Ronald Miller [mailto:rbmiller@xxxxxxxxxxxx]
> Sent: Wednesday, November 17, 1999 9:02 AM
> To: Patrick Gilliland
> Cc: stds-802-3-hssg@xxxxxxxx; si-list@xxxxxxxxxxxxxxxxx;
> hari@xxxxxxxxxxx; hweng@xxxxxxxxxxx
> Subject: Re: 10 Gbit Ethernet PMD
>
>
> Pat et al
>
> Back in 76 we tried to develop a bandwidth limiting data
> communications scheme called Partial Response. We violated
> the Nyquist criterion by setting our bandwidth at half the required
> bandwidth for the data rate and ended up with 7 levels. The signal
> could not make it from 0 to 7 in one symbol time so the other levels
> were generated.
>
> The end result was that we never finished because of the complexity
> of the filtering and also because of the obvious decrease in
> noise margin
> or in signal to noise ratio. Net result - no go.
>
> It looks like this multi-level signaling may be up against
> the same signal
> to noise ratio or noise margin problem. When one considers ripple
> in the rails seen in an eye diagram and assumes that these
> same ripples
> will occur at all the levels of a multi-level system the
> obvious eye-closure
> will be a real problem.
>
> However, if the ripple which is caused by reflection from
> impedance changes
> in the transmission lines can be reduced substantially it may
> work. Can the
> connectors, transmission lines and IC pins be made good
> enough to clean up
> this ripple. That is the gating question for this type of system.
>
> Getting back to your origional problem with the laser
> linearity, I do not believe
>
> that multi-level optical was the intent. I believe that
> multi-level signaling is
> being
> considered for the electrical connection to the optical
> device which would then
> convert it to 10 GB optical.
>
> Ron Miller
>
> Patrick Gilliland wrote:
>
> > Rich,
> >
> > It is true there are many advantages to the
> > use of multi-level signalling in copper based
> > Ethernet systems. There are also many other
> > examples to choose from to demonstrate the many
> > benefits of multi-level data encoding such as the
> > PAM5 or QAM4 you have suggested.
> >
> > However, these types of communications systems rely
> > on linear components at the transmitter and receiver
> > ends of the link. I believe you have correctly identified
> > this lack of linearity as one of the major problems to
> > be dealt with in any multi-level data communications system
> > employing a laser as the active element. My experience
> > with lasers teaches away from the direction of MAS. While lasers
> > can be relied on to some degree to be linear as FM transducers,
> > it is difficult enough to get them to work in a bi-level
> > AM application such as the 1.25Gbaud Ethernet data link.
> >
> > I admit some prejudice in this regard, but I feel the need
> > to comment because at some point, if we continue to work
> > along this direction, I might be asked to make such a transmitter.
> > I also disagree with the assumption behind the premise this
> > type of bandwidth reduction is necessary to accomodate the
> > optical fibers. The bandwidth of the fibers is clearly sufficient
> > to allow for inexpensive 12.5Gbaud transmission. It is no doubt
> > already being done by the telecommuncation companies of the world
> > such as Lucent, NEC, Alcatel, Nortel, etc. Their methods employ
> > single mode fibers and external modulators in many cases.
> >
> > The cost of these types of laser transmitters is relatively high
> > as you have stated. However, those in the business of producing
> > these components realize many of the cost issues are volume and
> > certification dependent. Many efforts are presently underway to
> > address the cost problem at the present time which may bear fruit
> > in a timely manner to the issuance of a 10Gbit Ethernet
> specification.
> > I apologize for my lack of enthusiasm, especially because of the
> > tremendous amount of quality work you have obviously put in on this
> > proposal. I will also give your proposal some additional thought.
> >
> > Maybe there is a way to overcome some of the difficulties which
> > are inherent in any multi-amplitude-signalling (MAS) laser based
> > optical link. I remain open minded but skeptical on this issue.
> >
> > Best Regards,
> >
> > Pat Gilliland
> > patgil@xxxxxxxxxxx
> >
> > -------------------------------------------------------
> >
> > At 03:33 AM 11/16/99 -0800, you wrote:
> > >Pat,
> > >
> > >Not at all. I've been pushing multi-level signaling
> scheme for 10 GbE since
> > >March. There are a number of presentation out there. I
> suggest working
> > backwards
> > >starting with the Kauai meeting. Here are the two best
> links for info:
> > >
> >
> >http://grouper.ieee.org/groups/802/3/10G_study/public/nov99/t
> aborek_2_1199.
> > pdf
> > >http://grouper.ieee.org/groups/802/3/tutorial/july99/mastut.pdf
> > >
> > >Patrick Gilliland wrote:
> > >
> > >> Rich,
> > >>
> > >> I have some questions based on my reading
> > >> of your latest posting and the presentations
> > >> you cited. In one of the studies, a mention
> > >> was made of multi-level optical transmission.
> > >> Is this a misread on my part?
> > >>
> > >> Pat Gilliland
> > >> patgil@xxxxxxxxxxx
> > >>
> > >> ------------------------------------------
> > >>
> > >> At 06:54 PM 11/14/99 -0800, you wrote:
> > >> >
> > >> >The purpose of this note is to clear up confusion
> regarding Hari, a
> > >> >proposed 4-lane serial interface for 10 GbE and
> train-up sequences.
> > >> >
> > >> >It should be clear that NO TRAINING SEQUENCES are
> proposed for Hari.
> > >> >Both the "Hari Coding Objectives" presentation
> > >>
> >
>(http://grouper.ieee.org/groups/802/3/10G_study/public/nov99/taborek_1_1199
> >> .pdf)
> >> >and "Word Striping on Multiple Serial Lanes"
> >>
>
>http://grouper.ieee.org/groups/802/3/10G_study/public/nov99/ritter_1_1199.p
> >> df)
> >> >make a point of noting that no train-up is required Hari to deskew.
> >> >
> >> >The Hari Coding Objectives proposal uses the standard Idle sequence
> >> >proposed by Howard Frazier of Cisco to deskew multiple parallel lanes
> >> >while simultaneously acquiring code-group synchronization on all
lanes.
> >> >
> >> >--
> >> >Best regards,
> >> >Rich
> >> >
> >> > ----------------------------------------------------------
> >> >
> >> >Richard Taborek Sr. 1441 Walnut Dr. Campbell, CA 95008 USA
> >> >Tel: 408-370-9233 Cell: 408-832-3957 Fax: 408-374-3645
> >> >Email: rtaborek@xxxxxxxxxxxxx
> >> >
> >> >
> >
> >--
> >Best regards,
> >Rich
> >
> > ----------------------------------------------------------
> >
> >Richard Taborek Sr. 1441 Walnut Dr. Campbell, CA 95008 USA
> >Tel: 408-370-9233 Cell: 408-832-3957 Fax: 408-374-3645
> >Email: rtaborek@xxxxxxxxxxxxx
> >
> >