On 02/22/2013 02:55:07 PM, Mick wrote:
On Friday 22 Feb 2013 08:04:38 Helmut Jarausch wrote:
> Hi,
>
> I have no experiences in debugging a slow network.
>
> At home, I have a router which is connected to my telephone line via
> VDSL2.
> I have 2 PCs one of which is connected by an ethernet cable (i.e.
> wired) while the other
> one uses a wireless connection which is specified as 56 Mbit/s.
>
> When copying data from one machine to the other one I see varying
> speeds from only 0.5 Mbits/s up to
> more than 20 Mbits/s. I have no idea why it is so slow some times.
> There are no other wireless devices nearby.
Where do you see these transfer speeds? On the wired machine, or on
the
wireless machine?
What do you use to check the transfer speed?
One tool is ttcp which is very similar to netcat and this concerns me
most.
The other tool is a remote webserver for measure internet speed
Do the speeds go up when you used a Cat5e cable at full duplex?
The PC which is wired doesn't have those problems since I can transmit
data from
my remote office machine at the highest possble rate which is specified
by my
internet provider.
Have you scanned for access points to be absolutely sure that there
are no
other wireless devices, or APs?
Do you use encryption?
Yes, but since I do get optimal performance "some time" I don't think
this
matters.
What frequency and channel are you on and have you tried to change
channel/frequency? (some domestic devices like cordless phones,
wireless
earphones, bluetooth, microwaves, perimeter sensors, etc. can cause
co-channel
and adjacent channel interference and/or force sharing of the
bandwidth).
Are both machines and the router's LAN on the same MTU?
Sorry, what's "MTU" ?
> What tools and techniques can I use to debug this situation?
>
> Many thanks for a hint,
First use ifconfig to see how many dropped packets you get on both
machines.
Then use iwconfig, or cat /proc/net/wireless on the PC running the
wireless to
see how many discarded packets you get, fragmentation, etc. as well
as nwid
packets from different networks on the same frequency.
Then check with e.g. iptraf-ng what network connections are running,
their
rate(s) and if any of these should not be there.
The router stats may also be revealing in this respect, as well as
dropped
packets on the WiFi.
I hope the above will give something to work with, others may have
better
ideas and more specialised tools for troubleshooting this.
Yes, that'll keep me busy a while.
PS. I haven't mentioned spectrum analysers to keep this thread
within the
realm of quick fixes, but if you do have EM interference and the
source of it
is obscure, you may need more professional equipment to nail this
problem.
--
Regards,
Mick
Many, many thanks Mick,
regards,
Helmut.
