The Natural Philosopher  wrote:
> On 12/01/2021 18:04, Chris Green wrote:
> > When I copy from laptop to desktop (both quite fast machines with fast
> > disks) I get something quite a bit over 100MB/s on wired Gigabit
> > connections.  So the overhead isn't that great given that the
> > theoretical maximum would be 1000/8 which is 125MB/s.  So on a 300Mb/s
> > wireless link between the same two machines one would, sort of, expect
> > something a bit more than 30MB/s whereas in reality one gets about
> > half of that.
>
> in general I have found that on a good link, speeds of a little over
> 1/10th Mbps rate to be obtained at the byte level, So overheads  is not
> that heavy a penalty.
>
> Probably ~10%

Yes, that's exactly what I was trying to say really, on a wired
connection one gets something over the 1/10 the Mbp/s in MBp/s.


> That's on a *full duplex* link. Broadband is full duplex. Ethernet of
> the cat 5 sort is full duplex.
>
> Wifi is NOT full duplex.
>
> That means that any ACK packets going back share bandwidth with the
> forward data stream, In a fairly nasty 'wait till the stream packet size
> is exceeded, then send an ack oh dear collisions/backoffs/try again...'
> sort of way.
>
Simply having to interleave the ACKs with the data going in the other
direction will slow things down considerably.


> When my Pi zero link was going titsup before I slapped in an access
> point 5 feet away, although it *said* it was connected at 5Mbps, it
> couldn't support a 128kbps stream of audio.
> My so called 72Mbps links couldn't handle HD TV, which is around 5Mbps I
> think, reliably.
>
I use WiFi for as little as I possibly can.  About the only major use
is using my laptop interactively like now, replying to usenet posts
and such.

--
Chris Green
·

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