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Re: Proposal for accomodating 10.0000 and 9.58464 line rates


Thanks very much for your patience in replaying my questions.  I agree your 
comments.  However, there are questions which you may like to respond   
> >  
>  We will need buffers in the PHY to accomodate the difference in MAC
>  and link speeds. I assume this will necessary anyway to allow for some
>  latency in the framing process.
> I agree we need buffers.   Using the numbers we are discussing, 10.000 Gbps 
+/- 100ppm and 9. 58464 Gbps +/- 100 ppm at the maximum frame size of 1500 
bytes, the worst case timing skew due to the data rate difference is 6.53ns.  
In other words, if the MAC/PLS and PHY interface is a byte-wide, the buffer 
size we need is 66 bit deep (byte) FIFO.  I believe Steve has mentioned 
before a short buffer, 64 bit deep.

The buffer size is small; therefore, buffer is not an issue at all.  On the 
other hands, if we make all IPG 64 bytes (or 66 bytes the worst case) in 
conjunction with 66 bit deep byte-buffer, theoretically, we are in good shape 
without any additional flow control.  Although the small packet, 64 byte, 
will slow down to 1/2 of the maximum throughput.  Is this suggestion causing 
other deficiencies? 

>  I am in support of a MAC/PLS interface that is un-coded data (as Shimon
>  suggested) and will therefore allow PHYs that use different coding for
>  their different environments. It is entirely reasonable to believe that
>  the coding requirements for a 40Km link will be different than those of
>  a 20m copper link.
I agree.  I do not have any quam with this. 


Edward  S. Chang

NetWorth Technologies, Inc.