Re: Debian server for backups of Windows clients
On Sat, 10 Sep 2016 10:53:20 -0400
rhkramer@gmail.com wrote:
> On Saturday, September 10, 2016 10:40:26 AM Gene Heskett wrote:
> > On Saturday 10 September 2016 10:26:15 rhkramer@gmail.com wrote:
> > > On Saturday, September 10, 2016 08:41:53 AM Dan Ritter wrote:
> > > > It's in megabytes per second, so assume 1000/8 = 250 MB/s is the
> > > > bandwidth of a gigabit ethernet NIC.
> > >
> > > Sorry, I tend to pick at nits, but, for the record, 1000/8 is 125
> > > Mb/s. It doesn't (really) change your conclusions.
> > >
> > > regards,
> > > Randy Kramer
> >
> > You make an assumption many folks do, but theres a start bit and a stop
> > bit so the math is more like 1000/10=100 Mb/s.
>
>
> Well, 1000/8 is still 125 ;-) but I wouldn't have written back just to say
> that. Isn't it the case that there is something less than 1 start and 1 stop
> for every byte--maybe like 1 stop bit for every several bytes? (I am just
> (slightly) curious.)
>
> And, iirc, there are variations (which may be obsolete--I seem to remember one
> protocol that had either 2 start or 2 stop bits?
Start/stop bits apply to async TIA-232.
Speaking very generally, 100Mb/s Ethernet actually operates at 125Mb/s; that includes the LAPB-like protocol that actually transmits the packets. All the layer 1 overhead goes in that extra 25Mb/s.
So, more correctly, you have data + TCP + IP overhead + L2 overhead: around 3% for full packets, higher for smaller packets. This is why 100Mb/s ethernet saturates at around 92%-95% *data* transmission. The rest is protocol overhead and delays (probably akin to RR and RNR).
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