10g residential CPE

Sat Dec 26 18:14:13 UTC 2020

lør. 26. dec. 2020 18.55 skrev Mikael Abrahamsson <swmike at swm.pp.se>:

> On Sat, 26 Dec 2020, Baldur Norddahl wrote:
>
> > It is true there have been TCP improvements but you can very easily
> verify
> > for yourself that it is very hard to get anywhere near 1 Gbps of actual
> > transfer speed to destinations just 10 ms away. Try the nlnog ring
> network
> > like this:
> >
> > gigabit at gigabit01:~$ iperf -c netnod01.ring.nlnog.net
> > ------------------------------------------------------------
> > Client connecting to netnod01.ring.nlnog.net, TCP port 5001
> > TCP window size: 85.0 KByte (default)
> > ------------------------------------------------------------
> > [  3] local 185.24.168.23 port 50632 connected with 185.42.136.5 port
> 5001
> > [ ID] Interval       Transfer     Bandwidth
> > [  3]  0.0-10.0 sec   452 MBytes   379 Mbits/sec
>
> Why would you just use 85KB of TCP window size?
>
> That's not the problem of buffering (or lack thereof) along the path, that
> just not enough TCP window size for long-RTT high speed transfers.
>

That is just the starting window size. Also it is the default and I am not
going to tune the connection because no such tuning will occur when you do
your next far away download and wonder why it is so slow.

If you do the math you will realise that 379 Mbps at 10 ms is impossible
with 85 K window.

I demonstrated that it is about buffers by showing the same download from a
server that paces the traffic indeed gets the full 930 Mbps with exactly
the same settings, including starting window size, and the same path
(Copenhagen to Stockholm).

Regards

Baldur
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