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Re: [EFM] Network timing, ATM, ADSL/VDSL and EFM


I very much like your comments about ATM, etc.  You are right.  There are 
lessons to be learned here.

If by "timing" you are referring to the "Stratum synchronization timing" 
that is associated with SONET/SDH optical services, don't worry.  The 
reason for the "timing" requirements has to do with directly multiplexing 
data signals at the electrical level within transmission equipment, for 
Example a SONET/SDH ADM.  T1/E1 timing is for much the same reason.

Ethernet is an asynchronous mapping data protocol.  It has worked that way 
for many years.  The only issues caused by that asynchronous mapping is the 
latency variance caused by transmit queue head blocking that occurs between 
large and small Ethernet frames.  For current technology switches that 
winds up being the difference between the bit times of the different size 
frames.  It becomes very apparent when doing a throughput/latency test 
using various frames sizes at different standard Ethernet speeds.

As for doing circuit emulation over Ethernet, don't bother.  It is Ethernet 
that customers are wanting to use as the protocol over "circuits".  We have 
Ethernet over SONET/SDH systems that are taking care of that.  Have you 
ever heard of "Ethernet Private Line".  It is an Ethernet interface on a 
SONET/SDH ADM that maps into a SONET/SDH payload that gets provisioned as a 
standard "Private Line" circuit across the transmission network, just like 
any other T1/E1.

Thank you,
Roy Bynum