Re: Cable characteristics [was: [10GBASE-CX4] WorkingPaperAvailable]
Chuck,
See response below delnieated with <HAB>
Howard
Chuck Harrison wrote:
>
> Hi, all.
>
> Sec. 54.8.2 'Cable Assembly Insertion Loss' sends a mixed message.
> Eqn. 54.3 is an inequality, and suggests that *any* loss curve
> which falls above the line in Fig. 54-8 is compliant. However
> the associated text places a 10% deviation limit on frequency
> response characteristic.
<HAB>
See my response to Steve Dreys similar comment.
<HAB>
>
> This is the tip of the iceberg on the variable-cable-length
> equalization issue. While the text of the standard does not
> need to say (and should not say!) how receivers are implemented,
> it needs to make it possible to implement reliable receivers
> using available technology.
>
> The most common thing for high-rate serial NRZI receivers that
> deal with variable cable lengths is to implement adaptive EQ
> at the receiver end. (E.g. SMPTE 292M Hi-definition TV at
> 1.485 Gb/s).
<HAB>
We are still in the processs of desiding what the specification should
indicate: all TX pre-emphasis, some tx and some Rx, adaptive rx, etc.
The gorup at this point has shwon a preferance for some tx and some rx
and not forcing an adaptive rx. We need to settle this prior to the
release for the March Plenary
<HAB>
>The channel is modelled as a variable length L
> of "typical" cable, so the receive EQ only needs to estimate
> *one* parameter (L) in order to apply an appropriate EQ curve.
> For coax a typical model is
> H(f, L) = exp(-(K1 * L * (1+j) * sqrt(f) + K2 * L * f) ).
> Note that this expression defines *both* loss and phase
> response, which can be important.
>
> I suggest that sec. 54.8.2 should be written to include the
> following features:
> (1) Both attenuation and delay dispersion should be controlled.
> (2) The cable-response formula should include a parameter L
> corresponding to "equivalent cable length"
> (3) The response of a compliant cable should be specified to
> be within a tolerance window (+/- 10%?) of the formula,
> for *some* value of L (not necessarily equal to the
> actual cable length).
> The resulting specification basically calls for any compliant
> cable to "look like" a length of the nominal cable, within
> some tolerance. This is a very reasonable requirement for
> cable vendors to meet, and a very tractable behavior for
> receiver designers to work with.
>
> Here is a useful reference from the IEEE ISSC conference a few
> years ago:
> http://iroi.seu.edu.cn/isscc99/digests/1999/DATA/23_3.pdf ,
> WP 23.3 "A 2.5Gb/s Adaptive Cable Equalizer".
> Sony Broadcast also published a white paper on the development
> of the 292M standard ca. 1998.
>
> On the transmit side, 54.7.3.6, the preemphasis is defined only
> by an example of behavior on a particular test pattern. While
> the intended behavior on other signals may be intuitively clear,
> it needs to be spelled out more clearly in order to properly
> ensure interoperability of compliant equipment.
<HAB>
If you could be more specific it would be helpfull. THanks
<HAB>
>
> Great work so far!
>
> Cheers,
> Chuck Harrison
> Far Field Associates, LLC
> +1 360 863 8340 (voice) PST = GMT-0800
>
> ddprocurve@antelecom.net wrote:
> >
> > 10GBASE-CX4 Study Group Members,
> >
> > In anticipation of the editorial review we will want to perform
> > at the upcoming meeting in Vancouver, Howard Baumer has provided
> > a copy of his working paper proposal.
> >
> > I have placed it on the 10GBASE-CX4 website at the following URL.
> >
> > http://grouper.ieee.org/groups/802/3/10GBCX4/wp2p01.pdf
> >
> > Please open and review that document and provide feedback to Howard as soon
> > as possible. You can reach him at hbaumer@broadcom.com.
> >
> > Regards,
> >
> > Dan Dove
> > Chair, 10GBASE-CX4 Study Group