How to ensure reliable wireless network?

[wolluf]

I support several schools which have mixed wired and wireless networks (3 schools I'm mentioning here). Each school has a number of the same make wireless access point deployed (4 dlink, 4 netgear and 5 netgear).
They all suffer from occasional 'outages' on the wireless network (all machines accessing it are laptops). By outages - usually means someone starts up machine which connected perfectly fine yesterday, and today it doesn't.

These seem to be caused by:-

people unplugging access points by mistake - obviously can't legislate for this!

access point 'going to sleep' - ie, looks like its working, but is providing no service. Simple power off/on solves - but why should it happen?

confusing hard wireless on/off buttons on laptops. This does my head in. There's no indication within windows that the connection is turned off (eg, the icon still appears in the tray, and if you try to connect it just can't). Some buttons are easy to press by mistake. Does anybody know of a way to override them, so wireless is always on (this for laptops with built in wireless of course)? Unfortunately, there are a number of makes and models of course, but one school has 12 Acer TravelMate 4072WLMi machines (and a number of other Acer TravelMates - can't find anything on Acer site about this).

some laptops just won't connect (after happily connecting for weeks on end). This may be manifestation of previous problem - but can take lots of 'cajoling' to get the connection back.

I set up 2 of these wireless networks and have added to the other one. The advice I read said to use different channels if the access points serve overlapping areas (which they do). In one school I have 3 on the top floor on channels 1, 6 and 11 and the 2 on the bottom floor on 1 and 11 (although there is overlapping between the floors too). In another have 2 on channel 6 and 2 on channel 11 (had problems when I tried more channels). Was wondering if would be better all on the same channel? Like one thing I don't understand is if an access point has 'gone to sleep', why machines don't pick up from one of the others. In most places in all 3 schools, at least 2 access points are within range.

Anyway - thanks for reading this - any advice gratefully received.

 

[wolluf]

PS. All client machines are running XP Pro, SP2 - and haven't had the recent upgrade that Bill Castner's been advising of installed.

 

[dput]

Our Dell and HP laptops all have indicators on them to show that wireleess is on (indicator light) and the wireless client in the system tray also shows whether the wireless is on or off. Don't know anything about Acer's.

On your Access Points, do all have them in a building use the same SSID?

It also sounds like you have a nightmare in regards to people unplugging Access Points and such. Can you get them into secured areas?

What type of security/encryption are you using?

Dan

 

[beridor]

first issue to address is your channels, definetly use the three channels 1,6 and 11 - but don't forget to consider the three dimensions (i.e. check above and below the ap you are installing.) To be honest this does not make a huge difference unless the network is busy - the beacons are only 10 per second and so don't cause a huge amount of "noise" in the environment.

you could check the bios to see if you could set the wireless cards in the laptops to always on - this would obviously be entirely dependant upon the bios. Not sure there is another easy answer to that one.

access points, even those supporting power saving should never go to sleep- that sounds like duff firmware to me (an ap in powersave mode should buffer frames but never go to sleep like a card).

as for unplugging the access points - shooting the people doing it, it definetly solved the problem for me

 

[bcastner]

Three channel: 1,6,and 11 are completely without overlap.
Four channel: The overlap with channel 4 is so small that 1,4,6 and 11 is perfectly feasible and often used.

http://www.dslreports.com/forum/remark,6683522~root=wlan~mode=flat''

But remember that most of this overlap of channels went out the Window after 802.11b. 802.11a and 802.11g (and 802.11n) use DSS and are not channel bound. They transmit on all channels (and in the case of 802.11n they do so simultaneously). You should be able to seamlessly 'roam' between APs if all authentication codes are identical among the APs.

SSID the same on all APs, set a 3 or 4 channel scheme. You can get AP density professionally mapped and AP site placement determined by several companies; CISCO comes to mind. The budget way is to use NetStumbler. (Rough, but better than nothing).

http://www.netstumbler.com/

As for 'sleep' this is a known issue for early chipsets from Broadcom. In all probability you could face the issue with a D-Link, Linksys or Netgear 'b' only access point. (b+g, a+b+g are not effected). For the Linksys firmeware resolved the problem eventually. Slighhtly more crudely, set you file server to ping each of the APs on some regular schedule. That is enough to keep them 'awake.'








____________________________
Users Helping Users

 

[wolluf]

Thanks for replies. AP's are all 'g' (probably worth checking out if later firmware available - though one 'set' has been purchased and installed in the last month. Problems only this week, after several weeks perfectly ok - which is what confuses me!) - should have mentioned. SSIDs and authentication codes all same for each network.

Schools are all primary - haven't got 'secure' areas for siting APs - and are subject to various staff - eg, cleaning staff - deciding they want to use the socket they're plugged into! (Obviously I've made the head aware of this, but haven't shot anyone yet!).

Bill - that crude 'ping' idea sounds worth trying. I think the coverage is perfectly ok when everything is operational. Its the 'sleeping' aps and the laptops that just won't connect (until, for example, you physically move them near a different ap - then they connect fine, and continue fine when taken back to original location! - or uninstall and reinstall the wireless device).

 

[wolluf]

Bill - crude ping didn't make any difference. I've just picked up on what you said about channels. These are all g APs and g wireless cards (though the APs are set to their default of b and g). If I set the APs to just use g, does that mean the channels are immaterial? Or are they anyway as all machines using g?

One thing - the 'sleeping' APs appear to cause similar effect on machines connected to them when they went to sleep (ie, these machines won't connect to any access point until the sleeping one has been rebooted. This is a partial observation so far - it appears to be true but can't be sure it is always happening).

Also - read some comments about power saving schemes on laptops causing this AP sleep (eg, when laptop goes into standby mode it takes the AP with it?) - anybody know anything about this?

 

[Kwazzy]

I like the diagram attachment from the thread that Bcaster linked us in another forum. This shows exactly why the 1-6-11 scneario is the only recommended method of channel setups. Or you can set your devices to Auto Channel. Which in return uses channels 1-6-11. However, this is not recommended by the manufactures, because it is a best practice to know you channels when setting and designing.

On the contrary, he also noted using a four channel setup, using channels 1-4-6-11. This is not a recommended setup. Go back to the diagram that was in the forum link. There you will see the over-lapping channels of 4 wide spread on to channels 1 and 6. Think of it this way, you are trying to best utilize the frequency range of the 2400-2475MHz. The channels are using roughly 22 MHz per channel. This will give you three NON overlapping channels. This goes back to the 1-6-11 channel break down. If you have an AP that is channel 4, next to an AP that is channel 1 or 6, any devices connecting using the overlapping frequencys will fail to recognoize the AP it is using to communicate to. It has nothing to do with roaming. You will roam from AP to AP, regaurdless of the channel. What you do have to be concerned about, is what channel your device is talking on when communicating to a particlar AP.