Some are good, some are bad...wireless situation

Hello folks,

I have installed 7 Access Points 1121G on my school. The AP are covering the space of 8 classrooms and there is some leaking of signal to the outdoors.

When I installed the system everything worked great (with my wireless laptop - Broadcom 54g MaxPerformance builtin card ). I was able to roam from one classroom to the last one without ever losing connection to my network

Problems are starting to show with some student's laptops, they claim that some days they have connection OK, but somedays not. I went there, tested everything again, and did not find a problem (using my laptop).

Because I am in the pilot phase, I dont' even have security on the WAN, Access Points are Open, no encryption. My only protection is that the Wireless Lan belongs to a VLAN that goes directly to the internet, it does not touch my internal LAN. Later I will increase security to avoid abuse of the service of course.

At first my recommendation to student who asked was to get Wi-Fi Certified NIC, but it seems that it does not matter....yesterday I was unable to make a MN-720 (microsoft) to get IP from my DHCP, signal strenght was great though. I used a fixed IP, and then I was able to ping externals hosts without problem...I could not solve the problem, because for some reason the DNS queries did not work...but that could be something extra.

I need some advises. Thanks a lot!!!
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In most case, the NICs will probably pick up the closest /strongest signal originally.  It should not try to pick another signal UNLESS the current one is very low.  Of course, that is, if you are using the same SSID.

One potential problem, however, could be the dynamic channel assignment you were talking about, however.  Not many people know this, but although you have 11 channels to choose from, in reality, you only have THREE...  1, 6, and 11...  WHY?  because although you assign 1 channel, each channel really crosses 2 channels on top or below it....  For example, if you have channel 6 assigned, it will take up part of channel 4, 5, 6, 7, and 8.

So why does this matter?  Because when you have channel overlaps, you might have problem with data tranmission, etc.  That's why when I setup my wireless network for my clients, I always manually assign channel for each access point... 1, 6, 11, then back to 1 again.  Especially when you can detect other AP's from your current position.  So basically, it is okay if you can "see" other AP around you, as long as the APs you see are not crossing over with your channels.

- Info
sometimes windows (dunno why) tells you have great signal strength even though you don't.
try rebooting the computer and turning on the wireless card (if it needs too) before turning your computer on
Follow these steps:

Turn off the Authentication and Internet Connection Firewall for the wireless card.

1.  Click on the Wireless Connection Icon in the bottom left corner of the computer screen
2.  Click on Properties when the Card Status Dialog box opens
3.  Click on Advanced
4.  Under Internet Connection Firewall make sure the box is UN-checked
5.  Next, click on Wireless Connections
6.  Under Preferred Networks click on the network name that you are using
7.  Click on Properties
8.  Click on Authentication
9.  Make sure that the Enable 802.11x authentication checkbox is UN-checked

Add the network to the Preferred networks

1. Click on Start>Network Connection>Your Wireless adapter
2. In the properties page under preferred networks make sure that your home network is listed first and that no other networks are listed
3.  Click on the Advanced button on the bottom and make sure that connect to non-preffered networks box is UN-checked.
4.  Make sure that the connect to access points only is checked.
5.  Close out the property pages

Change the channel and the SSID on the router to something other than the default.  You can check what channel and SSID the other router is using by downloading netstumber and running the program.  It will show what wireless networks are in the area the SSID and the channel they are using.

If it still drops the signal follow the step below.

In the properties for the wireless adapter click on configure.
You should see an advanced tab.
There should be settings that you can change.

One of them should be SSID or desired SSID.
Change the SSID to the SSID of your wireless network.

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Not all NIC are built the same.  Some have better signal receptions than others.  I've tried 3 different NICs and 3 different access points in my house before finally settling with what I have right now.  I am also in the Wi-Fi installation business, and have heard the same from my clients....   Signal reception can make A LOT of difference.

Dnigenda was also correct in saying that sometimes Microsoft would claim that the signal strength is excellent even though that's not the case.  It really depends on the NIC and its drivers.  For example, SMC's driver pretty much completely bypass Microsoft's utility, and it actually tells me I have full strength when my signal is next to zero.  Linksys, on the other hand, does a much better job with telling you the actual signal strength.

You should also make sure you do not have Internet Connection Firewall (or any kind of firewall) turned on, at least when you initially try to test the network.

Finally, 802.11b/g standard is not perfect.  It is sharing the same bandwidth/channel as a lot of common equipments, amongst which the most common ones are your wireless telephone and MICROWAVE OVEN.  That meanst that while you are testing, if someone is using those devices you could be getting a very different result as you'd normally get.

- Info
vandresvAuthor Commented:

I have already implemented my wireless network (7 Cisco 1121G access points) located in 7 adjacents classrooms. No security at all so far, open access to my network, as I said the only security I implemented was creating a VLAN only for the wireless acces, so there is no way somebody can hack inside my LAN, of course anybody can use/abuse my WAN bandwith (except that I limited the bandwith on the firewall).
The problem comes from some laptops that refuse to connect (like the MN-720 I told about it on my orignal post, and some others that were connecting very good on the first days of implementation, and now don't connect), or some others that were not able to connect at the begining (of implementation) and several days after they connect....It's like I don't have the grasp of this bussiness yet.
After reading the links that you talked about it, I found that I didnt have any concern with the channels assignation, why? cisco 1121 AP, listen to the air before assigns a channel to himself, so it gets always the less crowded channel, I suppose that I don't need to mess with this, so I leave it alone in his job. But maybe I am wrong, SSID is the same in the 7 active AP, and that explains why my laptop can roam perfectly among the 7 classrooms without loosing IP, and as  somebody said, you can notice a drop of the signal just before it switch from one channel to the other, and then the signal strenght grow strong again after the switch.

Do some Nics will have problem connecting if they receive strong signals from different channels ?   ---that could be a problem in my case, I have the feeling that I did overdo, and still can turn off, some of the AP, without loosing coverage....Could that be explanation of having unstability on the connections of certains laptops, but good behaviour on other models ?

In other words, Is it a bad sign if I turn on netstumbler and find out that my nic picks up signals with comparable strengths from different channels (different AP) ?  
Thanks again!

I have seen situations were some wireless cards that were 802.11b could not negotiate a connection to a 802.11b/g access Point.  Try changing the frequency on the Access points to 802.11b only to see if that makes a difference.

You might also want to play with some advanced settings on the Access Points.  Enabling CTS/RTS and Fragmentation on the AP's might help also (if it isn't already enabled).

On the AP look for an advanced setting tab, you should have a setting for CTS/RTS.  Enable it by lowering the number.  This requires some trial and error.

Article on Fragmentation

Hope this helps.


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