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The appropriate place to for nAUI chip to module electrical
specifications is in 802.3ba, not in other groups such as MSAs. There are a
number of reasons for this. 1. SMF 40GE and 100GE PMDs (LR4 and ER4) identify nAUI as
their retimed electrical interface. The PMD optical specifications are close to
complete, allowing implementers to proceed with specific implementations that
will be interoperable. In contrast, the PMD electrical interfaces have seen
very few contributions. To allow implementers to move forward with specific interoperable
implementations, a generic chip to module nAUI specification is required. 2. MMF 40GE and 100GE PMDs (SR4 and SR10) identify PPI as
their un-retimed electrical interface. Considerable progress has been made specifying
this interface, which will allow implementers to proceed with specific
implementations that will be interoperable. The same should be done for the
re-retimed PMDs. 3. 802.3ba will have a detailed chip to chip nAUI
specification. Specifying a variation of nAUI in another standard is a
prescription for conflicting interpretations. It is generally a bad idea to
have to look through two standards for the definition of an interface. 4. PMD electrical interfaces have always been specified in
one standard or another. XAUI was specified in 802.3ae; XAUI was not
specified in the XENPAK or X2 MSA. XFI (for XFP) and SFI (for SFP+) were
specified in MSAs, they were not specified in IEEE. The XAUI 802.3ae
specification underscores the problem we will face if we do not include a chip
to module component to nAUI in 802.3ba. XAUI is specified as chip to chip only,
with no allocation for additional connector loss or test points for module
applications. As a result, there is no solid XAUI chip to module specification
anywhere. 5. IEEE is the most rigorous and public forum for writing a
generic nAUI interface specification which will then enable interoperable
specific implementations. A specification in 802.3ba will have the broadest
possible pool of contributors and reviewers. 6. There is no body today, other then 802.3ba, that has the expertise to
complete the nAUI specification. If this is not done in 802.3ba, then many of
the same participants who are now working on the nAUI chip to chip
specification will have to organize themselves into another standards body to
write the chip to module nAUI specification. There are a number of arguments that have been raised
against doing the nAUI chip to module specification in 802.3ba. I have listed
some of these, with responses following them. 1. The specification can not be written because we have no
connector model. *** To write the spec, a generic connector model can be used,
based ether on an existing model such as used for XFP applications, or based on
a model provided by connector supplier(s) based on their best estimate of a
nAUI interface connector model. At least one company has such an
estimate model available. In any case, all the limits, such as connector loss
and cross-talk should be specified in general terms (for example such as the
ICR curve used in 10GBASE-KR.) It is then up to the implementers to design the
channel to meet those limits, such as choosing a specific connector. 2. The specification may not be applicable to future nAUI
applications, for example mezzanine
cards. *** The chip to module specification will be generic, assuming
generic connector, loss, cross-talk, etc, and will have conservative limits
applicable to a broad range of implementations. This is similar to the chip to
chip specification which is not limited to a single type of IC package
implementation. The chip to module nAUI specification will provide a reasonable
starting point for new implementations, and in most cases accelerate their
development. In the worst and unlikely case of not being able to meet the
802.3ba standard, a new specification will have to be developed which is no
worse then would be the case without an 802.3ba standard. 3. Since we are late in the 802.3ba cycle and we are trying
to have a complete specification in March, this specification can not be completed
in time. *** It is an unfortunate that the nAUI chip to module interface,
which is central to SMF PMDs, has seen so little contribution material
submitted. Part of this has to do with miscommunication and conflicting
assumptions made by various contributors with respect to what will get done and
where it will get done. Hopefully our poor progress to date will motive all of
us to quickly remedy our past oversights.
From: Mike
Dudek [mailto:Mike.Dudek@xxxxxxxx] During today’s XLAUI/CAUI Ad Hoc
call I picked up some action items to E-mail out some items.
Here are these items. 1
There was significant debate as to whether the XLAUI/CAUI IEEE specification
should be just for chip to chi, or whether additional test point specifications
should be included for host/module. Ie whether the host/module
specs for the retimed interface are included in 802.3 or left for development
by other groups such as MSA’s or SFF committee. Jeff volunteered to
ask CFP members their views, however I think it is an appropriate topic for the
complete group. (FYI The non-retimed PPI host/module
interface specs are being developed in IEEE in Clause 86). 2
Detailed specification discussion. Proposals have been made to define
rise/fall times and De-emphasis. To define rise/fall times in a
reproducible manner, particularly for waveforms with de-emphasis the 0 and 100%
levels have to be defined in an un-ambiguous manner. Clause 86 is
using the stable levels on the square wave pattern (the same levels as used for
OMA/VMA measurement). I think this is the best method, as I think
this probably best predicts system performance. Alternatives
are however the peak levels as defined for De-emphasis (see later), or the
average value of the center 20% of the eye diagram (as used to define zero and
one values in the eye diagram). A proposal has been made to define
De-emphasis as the ratio between peak-peak values and the stable one/zero
levels. Again un-ambiguous definitions are required for peak-peak
and stable one/zero. The proposal suggested that the square wave
pattern is used. The stable one/zero levels could be defined
identically to VMA (average value over center 20% of the one and zero levels of
the square wave). Other definitions are possible, but I see no
advantage in creating a different definition. For the peak values
it was suggested that it should be the value at 0.5UI, however on the call zero
time had not been defined. One definition that I think is reasonable is
the zero crossing time of the square wave. Another definition for the
zero time would be the zero crossing time of the 101010 pattern. (however
this has the disadvantage of requiring a 101010 test pattern that is not
presently defined.). Yet another definition could be to use
the mean crossing point as used to align an eye mask. There are
also other possible definitions that do not require establishing an exact zero
time reference. Peak could be defined as the peak value at any time
within an averaged square wave. Peak-Peak could be defined as the
amplitude of a 101010 averaged signal (again however this has the disadvantage
of requiring the 101010 test pattern). Personally I think the peak
value at any time within the averaged square wave is probably the easiest
definition and recommend it’s use unless there are reasons not to do
this. My second choice would be 0.5UI after the zero crossing of
the square wave. Mike Dudek PMTS Standards & Technology JDS Uniphase CO 80027 Tel 303 530 3189 x7533. mike.dudek@xxxxxxxx From: Dear 802.3ba Colleagues, I'd like to schedule the next meeting for the XLAUI / CAUI Ad Hoc as
follows: Friday December 19th 8:30am - 10:30am Dial-in Number (Canada & USA) :1 877 234
4610 Participant Conference Access code: 4405734 # (see below for additional
phone numbers) Presentations should focus on technical details / values related to the
nAUI specification. In particular, I would like to focus on the channel
specification & de-emphasis proposals. Anyone wishing to present, please follow the guidelines described on
the Procedure for Presenters web page: http://www.ieee802.org/3/hssg/public/presentproc.html If you are planning to participate please take a moment to read the
IEEE patent policy available here: http://standards.ieee.org/board/pat/pat-slideset.ppt.
* Participant Conference Access code: 4405734 # * Dial-in Number:416 883
8981 * Dial-in Number:1 877 234
4610 Best Regards, Ryan Market Manager Analog & Mixed-Signal Products Gennum Corporation Phone: 905 632 2999 x 1610 |