What's required to make wireless reliable?

[Rick Stevens]

Mark Knecht wrote:
> On Fri, 25 Mar 2005 19:29:27 -0600, Otto Haliburton
> <ottohaliburton at comcast.net> wrote:
> 
>>
>>>-----Original Message-----
>>>From: Mark Knecht [mailto:markknecht at gmail.com]
>>>Sent: Friday, March 25, 2005 7:01 PM
>>>To: Otto Haliburton
>>>Cc: Getting started with Red Hat Linux
>>>Subject: Re: What's required to make wireless reliable?
>>>
>>>On Fri, 25 Mar 2005 18:24:33 -0600, Otto Haliburton
>>><ottohaliburton at comcast.net> wrote:
>>>
>>>>
>>>>>-----Original Message-----
>>>>>From: Mark Knecht [mailto:markknecht at gmail.com]
>>>>>Sent: Friday, March 25, 2005 6:14 PM
>>>>>To: Otto Haliburton
>>>>>Cc: Getting started with Red Hat Linux
>>>>>Subject: Re: What's required to make wireless reliable?
>>>>>
>>>>>
>>>>>>>I've moved the router to all the convienient places. It got
>>>>>>>significantly better, but not nearly good enough.
>>>>>>>
>>>>>>>Thanks Otto!
>>>>>>>
>>>>>>>Cheers,
>>>>>>>Mark
>>>>>>>
>>>>>>
>>>>>>I don't think it has to be metal to work, in fact I am sure it does
>>>
>>>not
>>>
>>>>>and
>>>>>
>>>>>>move it vertical also, I mean to a higher location and I also have
>>>
>>>heard
>>>
>>>>>>that some brands are not as good as others so you might use the old
>>>
>>>Frys
>>>
>>>>>15
>>>>>
>>>>>>day money back thing and try a different brand to see if it is
>>>
>>>better.
>>>
>>>>>>
>>>>>I'm trying to set up my laptop with ndiswrapper so I can run around
>>>>>the house and do some tests. How do I change the default routes to
>>>>>stop it from using the eth0 as the default route and make it use
>>>>>wlan0?
>>>>>
>>>>>I.e. - currently uses eth0 to get to the gateway and I want it to use
>>>>>wlan0?
>>>>>
>>>>>Thanks,
>>>>>Mark
>>>>
>>>>I think you go to either system or system utilities and there is a
>>>
>>>network
>>>
>>>>device under there and you can change it there.  I am currently under xp
>>>
>>>and
>>>
>>>>I can't tell you exactly, but you will see it in the menu and you can
>>>
>>>use
>>>
>>>>its help to see how to use it.  Better still just google wlan0 it might
>>>
>>>help
>>>
>>>>better with the problem you are having.
>>>>
>>>>
>>>
>>>Well I figured out that I can do
>>>
>>>ifdown eth0
>>>route del eth0
>>>ifup wlan0
>>>route add default gw Netgear
>>>
>>>I can switch to wlan0 and it works. Actually I'm sending this from the
>>>laptop using wireless.
>>>
>>>However it's sort of strange but the results from iwlist wlan0 scan
>>>are not valid unless I do ifdown wlan0 ifup wlan0. Unless I do that
>>>the value stays the same no matter where I am in the house.

That is a bit strange.  I have found that the order in which things are
fed to iwconfig is significant.  It may be that the script sets things
in a manner that causes problems.  The
/etc/sysconfig/network-scripts/ifup-wireless script sets up the
wireless stuff in this order:

	mode
	nickname
	network ID (wireless domain)
	frequency/channel (if mode is Ad-hoc)
	sensitivity
	rate
	WEP key
	RTS/CTS
	frag
	ESSID

>>>-13db 12" from the router
>>>-36db here at my desk
>>>-50db in my son's room
>>>-63db in my wife's office
>>>-63db in the kitchen
>>
>>well, I am surprised that there is that much difference in the values, I
>>would have expected them to be approximately the same because of the
>>relative small distance from the router, but you are getting some type of
>>interference from something in your house.  To me the relative signal
>>strength should be approximately equal since there should be nothing
>>interfering with the signal.  If you were outside then it would be a
>>different situation, cause the signal can ride on electrical wires and other
>>stuff so it would be stronger in certain areas than others.  What would be
>>curious if you left your laptop do the processing you were doing in the room
>>with the router and see if it ever dropped reception.  If you assume that
>>the router is always putting out a signal at the same level then everything
>>that is 15 feet from the router should have the same db level then if you
>>move to 25 feet then those should be the same etc.  in a perfect world, but
>>obviously something is causing a drop depending on where you are in your
>>house, unfortunately you don't have the equipment to locate exactly what it
>>is.  But now that I look at the figures the relative strength in your son,
>>wife's office and kitchen are actually pretty close and your office is
>>obviously closer to the router.  Now that I look at it I don't see a
>>problem, probably something for Rick or a wireless forum to discuss.
>>
> 
> 
> -13db 12" from the router
> -36db here at my desk
> My desk is in the same room as the router but on the other side of the
> bed. Approximately 14 feet east of the router.
> 
> -50db in my son's room
> This machine is 14 feet east and 10 feet south of the router. Go
> through 1 wall to get to this machine.
> 
> -63db in my wife's office
> This machine is approximately 35 feet south of the router. The signal
> either goes through 3 walls or goes outside through a window and then
> back in through another window to where my wife's desk is.
> 
> -73db in the kitchen  
> This is 14 feet east and 55 feet south of the router. The signal most
> probably goes through 4 or 5 walls to get here.
> 
> Keep in mind that power drop on any signal from a point source drops
> as r-cubed. There is nothing between the 12" measurement and the 14
> foot measurement.

Uh, isn't that "r squared"?  I can't recall my power calculation stuff.
Decibels (dB) is a logarithmic measurement as well, so things may look
a bit weird.
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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-           "I understand Windows 2000 has a Y2K problem."           -
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