Re: SONET/Ethernet clock tolerance
Rich,
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.
http://grouper.ieee.org/groups/802/3/ae/public/terminology.pdf
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.
http://grouper.ieee.org/groups/802/3/ae/public/mar00/ishida_1_0300.pdf
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.
-----------------------------------------
Osamu ISHIDA
NTT Network Innovation Laboratories
TEL +81-468-59-3263 FAX +81-468-55-1282