[time-nuts] Raspberry Pi 4B Ethernet delay

[Tony Finch]

Hal Murray <hmurray at megapathdsl.net> wrote:
>
> The 10/100/1000 on Ethernet speed refers to net data rate.  The actual bit
> rate on the wire is faster to compensate for things like 8B/10B encoding.  For
> example, 100 megabit Ethernet is actually 125 on the wire if you look at it
> with a scope.

The symbol rate for gigabit is also 125MHz because it needs to fit in the
same bandwidth for compatibility with 100meg cabling and emissions
standards. It gets the higher data rate by using all the pairs
bidirectionally and by using more volage levels. All-pairs-bidi is why
crossover cables aren't a thing any more. (Except literalljust as I was
writing that sentence a colleague came into the office looking for a 10meg
crossover cable!)

Gigabit ethernet is pretty neat.

Tony.
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