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Re: [A bit OT] Diagnosing home network

Mark Fletcher wrote:
> My home network consists of 2 Debian machines, one Jessie and one 
> Stretch, an LFS mini-ITX machine acting as my firewall, another LFS 
> laptop that is connected only occasionally, a Windows 8.1 laptop, 3 
> iPhones of varying ages, 2 iPads, 1 Android tablet device, a couple of 
> other proprietary tablets and a Buffalo Linkstation that provides most 
> of the connectivity.

Quick google doesn't show any "Linkstation" devices with more than one
ethernet port (much less wifi).  Do you perhaps mean an "Airstation"?
Could you provide the model number, so we can look it up?

> [...]
> I have my doubts about cross-LAN throughput. For example, as I write I 
> am using WinSCP on the Windows 8.1 laptop to copy a movie file from my 
> Jessie box to the laptop. (The movie concerned is not copyright before 
> anyone asks). The Jessie box is connected to the LinkStation by wired 
> ethernet, and the Windows 8.1 laptop by WiFi. I am getting a transfer 
> rate consistently across the life of the connection of 880KB/s. I'd 
> expect it to be a lot faster than that. I checked the WinSCP software is 
> capable of limiting the connection speed, but is set not to.

880KB (we'll call it 1 MB) / kilobytes per second is about 8 megabits
per second (1 byte = 8 bits).  8 mbit is a touch low (but in the
"range") of what you can expect from 802.11g.  802.11n may also fall
this low, but generally only when there's interference / poor signal.

A VERY rough rule of thumb is that on a perfectly clear channel, you can
expect your throughput to be approximately 1/3 to 1/2 of the "on the
box" speed (so 802.11g - 54mbit/sec yields roughly 18-24 mbit) for ONE
device connected to the AP.

>From there, you have to divide up the available throughput by number of
clients (i.e. a given wifi client's speed is 1/n, assuming that all
clients are using the same technology).  So if your wifi was *perfect*
for 802.11g, and one client got 24 mbit -- 2 clients would average 12
mbit each, 3 would average 8, and so on.  

In addition to "your clients", you have to contend with neighbors on the
same channels (who add to the 1/n throughput troubles).  5 GHz helps
here, as it's less likely that the clients in your home will see the 5
GHz signal from your neighbors, even if you are on the same channel.

> [...]
> I'd like to be able to diagnose what's going on here, why the transfer 
> was so slow. Any recommendations for tools I should research? I am very 
> willing to read man pages etc, but am a bit lost where to start. Google 
> gave me a lot of Windows-based stuff which I could look into but I would 
> prefer to use Linux-based tools if possible.
> Pointers to tools I should research -- and even better, links to good 
> tutorials on those tools if you know any -- would be much appreciated.

iperf would be a solid start.  Run it from one machine to another (e.g.
the wireless laptop to a wired desktop).  Don't try running it on the
router / access point / switch (if you have any of those), as iperf can
be resource intensive, so you "lose" a lot of speed due to their
processor not being able to keep up with the packet generation.

Also check your wifi channel usage -- 2.4 GHz should be on channel 1, 6,
or 11 (if you're somewhere where 13 is allowed, you could try that too).
If you use any other channel (2-5 or 7-10), you're going to be getting a
lot of interference (and throughput losses) from your neighbors.

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