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10 Gbit Ethernet PMD


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


At 03:33 AM 11/16/99 -0800, you wrote:
>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
>starting with the Kauai meeting. Here are the two best links for info:
>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
>> .pdf)
>> >and "Word Striping on Multiple Serial Lanes"
>> 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,
>  ----------------------------------------------------------
>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