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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 Booth
bradley.booth@xxxxxxxxx <mailto:bbooth@xxxxxxxxxx> 
Intel Network Interface Division, Austin Design Center
(512) 407-2135 office
(512) 589-4438 cellular

		-----Original Message-----
		From:	Tom Truman [mailto:truman@xxxxxxxxxx]
		Sent:	Wednesday, March 15, 2000 10:13 AM
		To:	Ed Grivna
		Cc:	stds-802-3-hssg@xxxxxxxx
		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
		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