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RE: scrambling vs block coding

Regarding the scrambling vs coding arguement... we need to remember that we
still need some way of framing with any scrambling approach.... or are folks
assuming SONET-like framing when they discuss scrambling?   Coding allows
rapid acquisition as well (see Michael's point below at the end re: regens)
- another benefit?
This is growing into a fairly interesting discussion - are we going to see
relevant contributions @ the Couer D'Alene meeting?
Rohit Sharma
Optical Networks
San Jose, CA <> 

-----Original Message-----
From: Michael M. Salzman [mailto:msalzman@xxxxxxxxxx]
Sent: Tuesday, May 11, 1999 9:27 PM
To: stds-802-3-hssg
Subject: scrambling vs block coding

Hi all,
The many cogent arguments about this subject highlight the requirements
differences between long haul and LAN applications.  Although we have reason
to expect that the packets sent along the LAN would emerge unscathed onto
the long haul network, there is no fundamental requirement for those packets
to be encoded and modulated in the identical fashion.  The LAN environment,
whether SX or LX  will require Phy's that are cheaper, simpler and more
robust.   Long haul applications on the other hand may derive an
overwhelming cost advantage from the scrambling approach.   Thus the
interconnection gateway between the LAN and the Long Haul would have the
SX/LX phy's on the one side and some kind of a long haul port on the other.
That port could be a direct phy - for those cases where the signal simply
enters a dark fiber, or it could be a port of a DWDM mux, that would insert
the signal at a particular wavelength.
At the same time, a dual phy approach, leaves a few issues unresolved.
Among the benefits of the block coding approach is the ability to pass
pseudo-data elements back and forth on the link.  These capabilities are
most required for the long haul, where a quick recovery of the link is most
desirable.   Furthermore, the ability to differentiate the level of the link
problem in a long haul application is important.  It could be an amplifier
failure, or a sync loss, or total transmitter failure.
Furthermore, would it not be desireable to enable loopbacks at a low level
in the long haul link in order to idenitfy the location of the failed
component?  Such schemes are often done outside the payload.  One answer is
that 10 Gig links are likely to travel over a WDM infrastructure, providing
its own physical fault isolation, hence a separate mechanism would not be
required.  The flip side is that a block code with control codes would
provide that extra measure of protection.  Frame based approaches for
managing the link would require a full scale PHY and MAC at each device. 
Finally, retiming, regeneration muxing and switching devices along the way
would benefit from the more rapid clock and error recovery of a block code.
It would reduce the demands on them.  


Michael Salzman             Director of Business Development
                                                       Lucent Technologies 
Phone  408-871-4075                          Lan Systems Group
Home   408-867-5164                          150 Knowles Drive
Fax     408-871 4102                        Los Gatos Ca 95032
Cell      408-829-4425                  msalzman@xxxxxxxxxx