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Re: SONET/Ethernet clock tolerance


Almost all your description about SONET clock tolerance issues seems correct 
to me except just one point about SONET regenerator;

At 11:21 AM -0800 00.3.28, Rich Taborek wrote:
> SONET performs clock tolerance compensation via the manipulation of pointers
> which involves significant modification of the SONET stream. My observation is
> that wherever SONET framing is employed in link with a clock tolerance of +/-100
> PPM that SONET reframing must be performed at any link point where clock
> tolerance compensation is required. After all, this is the same methodology
> employed in a SONET ring where a regenerator is periodically employed to ensure
> the SONET stream meets its +/-4.6 PPM requirements.

The things in a SONET ring are much worse.

SONET regenerator never performs the clock adjustment.  It recovers the clock 
from the received upstream signal, and use it for downstream signal to transmit.
Therefore SONET regenerator has very stringent (you may read it crazy) jitter-
transfer specification and hence is very expensive.

This was reasonable when SONET OC-192 accommodates thousands of 1.5 Mb/s T1 Path 
whose clock are all independent to the others; we didn't want to re-write 
thousands of pointers at each regenerators.  Brief description on this matter 
is in the Backup Foils pp.26-30 (What is SONET?) on my Albuquerque slides.

Here 10 Gigabit Ethernet will require only ONE Path STS-192c in the payload. 
I don't believe re-using expensive SONET regenerator for 10GbE is a good choice 
unless you have already invested in it.

I hope to see that 802.3ae will provide much economical solution for their own 
regenerators or media converters. 

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