Re: [10GBASE-CX4] Working Paper Available on IEEE site
Kamal,
kdalmia@marvell.com wrote:
>
[...]
> Instead, I believe, the RX and the Channel should be specified (with TX
> implied). Current XAUI specs have RX sensitivity and jitter tolerance
> numbers. This implies that the burden is on the TX to deliver a "clean" eye
> at the RX.
The big difference between CX4 and XAUI is that we now need to
tolerate a dramatically larger range of channel-loss behaviors.
An architecture which uses fixed TX preemphasis and a single-
parameter cable model gives RX designers a well-defined problem
to solve. It allows (but does not require) RX eq based on
estimated cable length. If you invert this -- fixed RX behavior
and vendors trying to put their smarts into transmit EQ -- you
can never get as good a system result because the TX side has
no way of knowing about the channel characteristic. And if
both TX and RX sides (not to mention the cable vendors!) are
blindly trying to be "smart" then interoperability is at
serious risk.
In the variable-channel CX4 environment, I would *strongly*
lean towards Howard's proposal -- fixed TX step response, and
a narrow tolerance on the channel's deviation from the nominal
cable model.
Cheers,
Chuck Harrison
Far Field Associates, LLC