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RE: 20 / 100 ppm


I don't understand your comment. The accuracy of the clock in ppm doesn't
imply the amount of jitter on the transmitted signal. To put it another way,
100 ppm clock tolerance changes the UI by less than 10 femtoseconds and 20
ppm would cut that down to 2 femtoseconds. Jitter on the received signal is
on the order of 10's of picoseconds.


-----Original Message-----
From: Jugnu Ojha [mailto:jojha@xxxxxxxxxxxxxxxxxxx]
Sent: Tuesday, May 08, 2001 5:30 PM
To: 'pat_thaler@xxxxxxxxxxx'; benny.christensen@xxxxxxxxx;
Subject: RE: 20 / 100 ppm


Although I'm not an expert on this issue, I can propose some reasoning
behind some of the cost statements being made.  Presumably, clock recovery
should be easier with a lower-jitter signal (20 ppm), since the signal is
effectively cleaner (i.e., you should need a lower-Q resonator - another way
of saying the resonator doesn't need to be as robust against jitter).
Basically, a cleaner signal relaxes the requirements on the receiver.  Now,
this should only matter much if it makes the difference between having an
integrated resonator or a discrete one - the latter would increase costs
associated with packaging, yield loss, etc.  


Jugnu J. Ojha, Ph.D. 
Technical Advisor, Optical Networking 
Caspian Networks Inc. 
(408) 382-5213
fax:  (408) 382-5588