fxp performance with POLLING

Pete French petefrench at ticketswitch.com
Tue Oct 7 20:53:09 UTC 2008

> That was a rule of thumb in the heyday of async serial lines, which used 
> a start and stop bit per byte.
> However, ethernet at 100Mbit is 4B5B coded at a 125mhz rate. So the raw 

Errr, 4B5B *is* 10 bits per byte surely?

> Even in the later days of modems this rule applied less and less, 
> because the modulation schemes became synchronous.

Gig ether is mainly 8B10, as is Firewire, SATA, FibreChannel and a
load of others I can't remember off the top of my head. I wouldn't
stay it's a hard and fast rule, but it still gives a better estimate
than dividing by eight which is what people naiively do.

Mind you, it assumes that you know the real bit rate, which in the
case of 100baseT is, as you say, actualy 125mbits/sec.


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