Re: [gentoo-user] Slow local network - how to debug?

[Mick <michaelkintzios@gmail.com>]

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On Friday 22 Feb 2013 14:36:22 Helmut Jarausch wrote:
> On 02/22/2013 02:55:07 PM, Mick wrote:
> > On Friday 22 Feb 2013 08:04:38 Helmut Jarausch wrote:

> > > 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

I suggest that you troubleshoot speeds across your LAN first, before you look 
at connections across the Internet which tend to be less consistent.


> > 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.

What I'm saying is:  When you connect BOTH machines to your router with cat5e 
cables does the performance improve?

I didn't know that you were using ttcp and was trying to eliminate other 
bottlenecks, e.g. storage caching, or drive controller problems if you were 
transferring a file.


> > 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.

Right, inconsistent performance could be due to interference, rather than 
someone free-riding your open WiFi network.


> > 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).

This may eliminate interference problems, but only if concentrated on a 
particular frequency.  Broadband transmissions will still interfere.

You could try moving your laptop around the premises to see if you can spot 
some device/appliance that may be causing this.

> > Are both machines and the router's LAN on the same MTU?
> 
> Sorry, what's "MTU" ?

  http://en.wikipedia.org/wiki/Maximum_transmission_unit

I was trying to see if there is a mismatch which may cause excessive 
fragmentation.

-- 
Regards,
Mick

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