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RE: [Fwd: Xaui jitter tolerance]

1/1667 is a convenient bandwidth for SAW filters which were
the prevalent clock recovery technology at the time Sonet
was composed.  A maximum specification for jitter bandwidth
is necessary to limit jitter accumulation in a cascade of
repeaters.  It is necessary for all repeaters in a cascade
to have the same jitter tracking bandwidth else those with
a small bandwidth will fail to track the jitter accumulated
by those with large bandwidth.  While it is necessary for all
repeaters in cascade to be similar bandwidth, there is nothing
special about 1667 related to this.

Ethernet has no regenerator defined so there is no need for 
a limited jitter bandwidth.

Larry DeVito
Analog Devices RSTC-121, 
804 Woburn St, Wilmington MA 01887
vox= 781 937 1323  fax= 781 937 1010
email= lawrence.devito@xxxxxxxxxx

From owner-stds-802-3-hssg@xxxxxxxx Fri Dec  1 14:56:27 2000
Subject: RE: [Fwd: Xaui jitter tolerance]


I agree that we should try and figure out why the 1667 was originally picked
in SONET, but I don't agree that I'm proposing a radical difference.  As FC
or GbE exists today there is no "max" value for this corner in jitter
tolerance, only a "min".  So if you track all the way to 100MHz you would
still meet spec.  As a practical matter, it's also probably true that many
designs already track to ~10MHz or so in parts today.

- Richard