RE: 8b/10b and EMI
Does scrambling give better spectral density than 8b/10b? I was under the
impression that scrambling has longer run lengths of 1's or 0's compared to
8b/10b. Does this not make it harder to perform clock and data recovery
with just a single scrambler, hence the reason SONET uses two scramblers?
Just curious,
Brad
Brad Booth
bradley.booth@intel.com <mailto:bbooth@Level1.com>
Intel Network Interface Division, Austin Design Center
(512) 407-2135 office
(512) 589-4438 cellular
-----Original Message-----
From: Tom Truman [mailto:truman@lucent.com]
Sent: Wednesday, March 15, 2000 10:13 AM
To: Ed Grivna
Cc: stds-802-3-hssg@ieee.org
Subject: Re: 8b/10b and EMI
<< File: Card for Tom Truman >> Ed,
Thanks for the response.
If 8b/10b were to be scrambled, then it would appear
to me that all it is providing at the XAUI interface is
packet delineation
and some error monitoring capability. I imagine that each
lane would need
a separate scrambler/descrambler, initialized to different
states so that
the transitions across the lanes are uncorrelated.
Synchronizing these
scramblers,
and deskewing the lanes would require some thought -- it
isn't difficult,
but it isn't as straightforward as the "alignment column"
proposed for HARI.
At that point, the 25% overhead of the 8b/10b scheme
seems to be a staggering price to pay for delineation and
error monitoring -- why not start with scrambling, at a
lower baud rate, and
make the overall design problems simpler?
Best regards,
Tom Truman
Lucent Technologies