[802.3ae_Serial] Draft comments
As requested, my wish list in the form of draft comments for discussion on
tomorrow's serial PMD phone conference.
Clause SC page line comment / remedy
----------------------------------------------
30 30.5.1.1.4 63 39 enmeration
enumeration
45 45.2.3.16 226 1 Draft says "The test pattern error
counter ... contains the number of errors received .... This counter will
count either block errors or bit errors dependent on the test mode (see
49.2.12)." But 49.2.12 says "When an isolated bit error occurs, it will
cause the PRBS31 pattern error signal to go high three times... The test
pattern error counter shall increment once for each bit time that the PRBS31
pattern error signal is high.
Clearly, clause 45 is misleading, because the counter does not report
received bit errors, but around three times as many counts as received
errors. You can't call the output of the checker "bit errors", that's what
is at the input of the checker; the signal coming out of the checker is not
an error or in error, but deliberately created. It has to have a different
name.
It would be a disservice to anyone trying to write MDIO software and report
received errors, without taking time out to understand the detail of the
other clauses, not to tell him that he may need to divide the counter value
by 3 to get a good estimate of received errors.
Remedy: "bit errors" with "asserted
bits at the bit error checker output". Add another sentence "In the latter
case, a good estimate of received bit errors may be made by dividing the
counter's contents by 3."
1 1.3 7 1 52.9.4 refers normatively, as I see
it, to ANSI/TIA/EIA-526-4A-1997 which is informative reference [B13] in IEEE
Std. 802.3 Annex A, which by the way should say (OFSTP-4A) not (OFSTP-4).
52.9.7 uses a "should" so maybe that's informative.
The entry presently in Annex A needs
copying or moving to the list of normative references, 1.3, (OFSTP-4A)
replaced by (OFSTP-4) and (if moved) the [B13] removing. Note 38.6.3 refers
to it in a way that looks normative but 38.6.3 is a variation on what
ANSI/TIA/EIA-526-4A says.
52 Table 52-18 469 12 There can't be as much as 0.5 dB
additional insertion loss allowed at 30 km because we can't know that the
path penalty will change by that much in the last 10 km.
May have to be 0 dB.
52 52.9.6.2 474 25 Number on different line to unit
Use nonbreaking space
52 52.9.6.3 475 9 Wrong step, as Petar pointed out
step c)
52 52.9.7 475 17 as per
per ?
52 52.9.7 475 45 As I understand it, measuring the average
timing of the edges away from the crossing level (waist) introduces a new
form of error, because the scope will sample a random proportion of rising
edges vs. falling edges, which then occur at different times. For typical
sample sizes, this creates a random timing error which largely negates any
benefit of moving the expected timing to the desired place. In the example
I looked at we were talking 1 ps.
The mask dimensions are not chosen to 1 ps precision.
Mask measurements are disappointingly inaccurate already. This would make
it worse.
The mask is not the primary measure of transmitter quality; TDP is.
There is an industry standard way of mask alignment already. It adds cost
and confusion to all users, on an ongoing basis, to create another way of
doing it.
Greg LeCheminant can elaborate.
In other words, don't re-invent the wheel. We pay test equipment
manufacturers to do a good job, let them!
Remedy: Delete "measured at the
average value of the optical eye pattern".
52 52.9.10.1 477 14 50.3.8 should be a link
activate
52 52.9.10.1 478 49 After further analysis, I think
specifying "fourth-order Bessel-Thomson" here is actually counterproductive.
There is no point tightly defining the filter and allowing very loosely
specified amounts of sinusoidal amplitude interferer (particularly) and
sinusoidal jitter. We don't know enough to really tie down the spec for the
stressed eye generator, so let's give the test equipment implementer a
chance to do the right thing.
Remedy: delete "fourth-order
Bessel-Thomson" here and in Figure 52-10, and "Bessel-Thomson" on next page
line 4 and 15. Could use " A linear phase filter" on first use: the phrase
occurs later on.
52 52.9.10.1 479 9 Breaks the one shall per test rule
must be
52 52.9.10.1 479 16 Here we could hint at the bandwidth
of the filter (around 3.75 to 5 GHz). Did we discuss this last time?
Giving this guidance would tend to keep implementers away from extreme
values of the sinusoidal terms and make for a more consistent test across
the industry.
Remedy: Add sentence "An electrical
bandwidth of 3.5 to 5 GHz may be found appropriate."
52 52.9.10.1 479 5 Does a filter with wide and flat
frequency response and linear phase response do anything? Even
Bessel-Thomson filters don't have flat frequency responses.
Remedy: replace "flat" with
"smooth".
52 52.9.10.1 479 15 These two sentences are out of line
with good practice as in 52.9.7 and G.691 and if taken literally, would give
the stressed eye generator implementer an unnecessarily hard task.
Remedy: Replace "The Bessel-Thomson
filter should have the appropriate frequency response to result in the
appropriate level of initial ISI eye closure before the sinusoidal terms are
added. The O/E converter should be fast and linear such that the waveshape
and edge rates are predominantly controlled or limited by the electrical
circuitry."
with
"The test pattern generator, filter and E/O converter should together have
the appropriate frequency response to result in the appropriate level of
initial ISI eye closure before the sinusoidal terms are added. The O/E
converter should have a linear response."
52 52.9.10.2 479 42 Ambiguous. Also I thought we had
scrubbed this use of "peak" per a comment last time.
Remedy: Replace "For this test,
these two components are defined by peak values that include all but 0.1%
for VECP and all but 1% for jitter of their histograms." with "For this
test, VECP is defined by the 99.9th percentile of the histogram of the lower
half of the signal and the 0.1th percentile of the histogram of the upper
half of the signal, and jitter is defined by the 1st and 99th percentiles of
the jitter histogram."
52 52.9.10.2 479 47 Text jumps abruptly into a recipe
without enough flags for the reader.
Remedy: Replace "Steps:" with "In
steps 1 to 7 below, a suggested method of calibrating a stressed eye
generator is described in detail."
52 52.9.10.2 479 52 Missing word
but this increases
52 52.9.10.2 481 3 Here is where we try to keep the
pulse shrinkage within a range.
Insert after "at least 5 ps": but
preferably no more than 15 ps" (peak-peak of pulse shrinkage jitter).
52 Figure 52-11 481 12 P1 and P0 look like the 1 and 0
levels: if so they should be next to the horizontal lines, not the histogram
boxes.
52 52.9.11.3 483 21 "The clock recovery unit" Which?
This is the first time one has been mentioned in 52.9.11.3. Also, number on
different line to unit.
Remedies: "A clock recovery unit",
use nonbreaking space.
52 52.14.2.1 488 27 Can we go forward with
"TIA/EIA-492AAAC is presently in ballot."?
52 52.15 491-5 As Peter pointed out, each
conditionally mandatory PICS needs a N/A []
I'm out of time, may add a few more tomorrow but this is most of it.
Piers