Signaling ad hoc (October 22, 2004)
Mike Altman begins his presentation
(http://ieee802.org/3/ap/public/signal_adhoc/altmann_s1_1004.pdf)
- [Joe
A.]
What are the simulation conditions?
- [Mike
A.] They have
been implicitly included in the ‘link elements
definition’
- [Joe
A.]
In one case you say that the methodology should not be simulator-dependent.
Yet both methodologies presented so far rely on a specific simulator. Where
do we stand with this ?
- [Mike
A.] This was a
discussion we had in the past. So far the direction has been to be simulator
independent.
- [John
d’A.] There never was a
straw poll.
- [Mike
A.] Right, but
it never appeared to be a subject of disagreement.
- [Charles
M.] It’s not clear that different simulators
would yield same outputs.
- [Mike
A.] Let’s table
this discussion for now. If you feel that a single simulator is ‘a must’ I
must ask you to make a formal presentation on the
subject.
- [Joe.
A.] Fair
enough. The only reason I am bringing this up is because the discussed
methodologies were certainly based on the concept of a common
simulator.
- [Tom]
Would it be simpler to just measure the eye
opening?
- [Mike
A.] I am not
thinking so much as a comparison of implementations but rather as an attempt
to define a “penalty box” to be used as a common derating
factor.
- [Jeff
S.]
I agree that these effects should be included so as to capture the “shape”
of the eye.
- [Petri]
This voltage margin number seems related to the BER calculation. Is it not
redundant?
- [Joe
A.]
I agree.
- [Mike
A.] Well, that
is true if I include random effects. I could consider just ISI for the
purpose of determining these margins.
- [Richard
M.] Are you concerned about the asymmetry of
the eye?
- [Petri]
The point
I am making is that this voltage/timing margin should be a subset of the
BER calculation.
- [Adam
H.] A fairly common method
has been bathtub curves, The voltage and timing margins are just a different
way to report the shape of the same function.
- [Xiao-ming]
If you add noise that would be better.
- [Mike
A.] This is for
us to agree upon.
- [Adam
H.] I think that this group
at a bare minimum should provide guidance on;
- reporting a
consistent set of metrics
- reporting
assumptions [used in deriving these metrics] in a consistent
way
- [Petri]
In the past different signaling schemes were selected by looking at the
channel capacity.
- [Adam
H.] 10Gbt was the only one
case where this criteria was used.
- [Petri]
CX4 did not use this criteria because there was not a debate on
signaling.
- [Steve
A.] If you start
from channel capacity this may lead to a complex
solution.
- [Vivek]
I was involved in the 10Gbt. Capacity defines the best we can achieve. The
next step is comparison of the margins associated with each signaling
scheme. This still does not shed a light on the implementation complexity.
If we agree on the channel model, this should be
straightforward.
- [Mike
A.] Capacity
would be a concern only if there was a doubt a bout the capacity of the
backplane. We are past that hurdle. What I am hearing is that focus should
be on the complexity of the implementation.
- [Vivek]
A shortcut would be to compute the SNR for the different
schemes.
- [Mike
A.] But you
would still need to report BER, voltage and timing
margins.
- [Vivek]
Voltage margin is what I am talking about. Timing margin is
trickier.
- [Mike
A.] My reasoning
for specifying the BER is that this is what I ultimately care
about.
- [Brian]
I am very skeptical about using SNR. BER is the metric to consider. SNR has
an implicit assumption of Gaussian statistics that fall apart at high
BER.
- [Mike
A.] So you see
the use of Gaussian statistics as incorrect?
- [Brian]
Yes.
- [Joe
A.]
I have a question on power which I consider a critical metric. The concern I
have is that power is a competitive metric. Assuming we go beyond
confidentiality issues, it will be extremely difficult to do an apple to
apple comparison.
- [Vivex]
In 10GbaseT most people had agreed on the basic architecture and building
blocks (transmitter, equalizer …). Once the blocks were agreed upon
(independently of signaling) it became possible to compare them in terms of
taps, speed etc. So we built a matrix with all this information. The various
participants reported numbers for textbook implementation
approaches.
- [Joe
A.]
This seems reasonable.
- [Mike
A.] The concept
of a ‘vanilla architecture’ is interesting and is part of what I was
considering in the presentation I made in Portland. Two
questions: is this agreeable? Is there an example we can refer
to?
- [Vivek]
Yes.
- [Mike A.]
Would you be able to
make an attempt at defining it?
- [Vivek]
Yes. I will circulate this among the participants.
STRAW POLL #1: Should we establish a
detailed power and complexity reporting matrix?
Yes: 27
No: 0
Abstained: 0
STRAW POLL #2: (a) Should we
establish BER as a signaling quality metric?
Yes: 19
No: 2
Abstained: 0
(b) Should we establish a min BER target?
Yes:
7 No:
9
Abstained: 5
STRAW POLL #3: Should we require
reporting voltage and timing margin at the BER levels of 10-12, 10-15 and
10-18?
Yes:
18
No: 0
Abstained: 3
Follow-up meeting scheduled for Friday
29 October 2004. Bridge and mtg info will be distributed..
Attendance:
Joe |
Abler |
Andrew |
Adamiecki |
Michael |
Altmann |
Stephen |
Anderson |
Majid |
Barazande-Pour |
Brian |
Brunn |
Joe |
Caroselli |
John |
D'Ambrosia |
Adam |
Healey |
Mike |
Lerer |
Cathy |
Liu |
Richard |
Mellitz |
Charles |
Moore |
Tom |
Palkert |
William |
Peters |
Petre |
Popescu |
Shannon |
Sawyer |
Jeffrey |
Sinsky |
Fulvio |
Spagna |
John |
Stonick |
Dmitri |
Taich |
Vivek |
Telang |
Brian |
Von Herzen |
Nirmal |
Warke |
Chris |
Wittensoldner |