RE: Gearbox reality check

["Booth, Bradley" <bradley.booth@xxxxxxxxx>]

8b/10b is mutually exclusive of 64b/66b.  The data out of the MAC is 8b/10b
encoded for transmission across the XAUI interface, it is then decoded at
the other end and re-encoded into 64b/66b by the PCS logic.

Clear as mud?

Cheers,
Brad

		-----Original Message-----
		From:	Erik Trounce [mailto:erikt@xxxxxxxxxxxxxxxxxx]
		Sent:	Wednesday, June 21, 2000 8:57 AM
		To:	Booth, Bradley
		Cc:	HSSG
		Subject:	RE: Gearbox reality check

		Brad,

		Ben, does this question sound familiar?

		My view of this so far is that without the WIS (i.e. UniPHY
LAN
		mode), data coming out on the OIF/SUPI interface is simply
the PCS
		output, albeit at a slightly higher rate.  For example,
assuming
		a 16-bit OIF network interface and an XGMII MAC to PCS
interface,
		the clock rate on the OIF is 644.53125 MHz, and the data is
66-bit PCS
		codewords, split up 16-bits at a time.

		Now, if you add the XAUI interface between the MAC and PCS
		which includes the 8b/10b encoding, I think you need to go
even
		faster on the OIF interface (805.6641 MHz!), to maintain 10
Gb/s
		from the MAC.  This can't be right.  Are 8b/10b encoding and
64b/66b
		encoding mutually exclusive?  Or is the 8b/10b encoding only
used
		across the XAUI interface with the two XGXS interface layers
		encoding/decoding the RS data (MAC sends ethernet, RS
encodes as
		XGMII, XGXS does 8b/10b encoding, sent across XAUI, XGXS
8b/10b
		decodes, PCS receives XGMII data, performs 64b/66b encoding,
etc).

		Can anyone clarify?

		Thanks,
		Erik Trounce

		In message "Gearbox reality check", Booth, Bradley writes:
		>Ben,
		>
		>Gold star!
		>
		>Now, can you explain how it works without the WIS? :-)
		>
		>Cheers,
		>Brad