Wireless networks and large groups of laptops

[maniac]

Hello,

 

Well as you can tell I'm new here and straight in with a question. Has anyone on here (I bet loads of you have) had experience with large groups of laptops (30 or so) using a wireless network all in one location?

 

I ask because someone had the bright idea of buying a trolly of laptops for the school I work in (and didn't consult us before making the purchase) and we've had nothing but trouble with them, particulalry at login. My conclusion is that the wireless access point(s) can't cope with that many workstations all trying to use them at once, and our advice to SLT has been not to buy any more wireless gear for students as it simply doesn't work reliably enough. Problem is they're dead keen on the idea of wireless laptops for student use and want to buy more, so we're keen to either find a way to make it work reliably, or find enough evidence to present to them to convince them it's a bad idea.

 

We've been using a wireless network for staff sucessfully for a number of years now with relatively few problems, but it just doesn't work reliably for students. For your information, the access points are 3com and are only 5 months old with the latest firmware loaded to them. The signal strength in the rooms they're used in is good to excellent in most locations.

 

One or two laptops on their own work ok, any more than about 5 at once and we're having trouble.

 

Any help or advice appriciated.

 

Mike.

[Geoff]

Your experience is about average for the kit and situation you have. Your advice you've given to SLT is correct. Current technology (802.11g) can't deliver reliably what your asking of it.

 

The reason is that WiFi is a shared medium (just like old BNC networking or 10mbit hubs) so eventually you just run out of 'space' in the radio channel the AP is using and laptops start interfering with each others signals. Eventually, you get to the point where there is nothing but signal noise. Then it all falls apart.

 

Wait a few years and try again with WiMAX (also 802.11n might work, but I've no experience of it).

 

The odd teachers laptop on WiFi should be fine though. So sticking an AP in the staffroom, meeting rooms for example is a worthwhile exercise.

[maniac]

Thanks for that, that sums it up nicely for me, and if anything makes me rest easier knowing it's not anything we're doing wrong!

 

The odd teachers laptop on WiFi should be fine though.

 

We have over 100 teachers laptops on a school wide wireless network (and they all work fine)

[eean]

Trouble with any more than 5?? That sounds a bit rubbish! There's probably something wrong there.

We have 15-20 on one AP without any trouble - occasionally, if they all hit the logon button at exactly the same time, group policy won't apply correctly to ONE of them, but that's fixed by logging off and back on.

 

You may have to go with a more commercial-grade wireless network - like blue socket or some of the cisco stuff. Some folks on here have experience of this. Basically, you have a controller, server end, then 'dumb' access points. The controller can then load balance the clients across several access points. At the moment, all the clients will attach onto the loudest ap even if it has 30 users on it and there may be a slightly weaker signal a few doors down with none on it. They can also automatically 'turn down' some APs and switch channels.

 

(Our aps will pick their own channel - you have changed away from the defaults haven't you?) You also may want to look at the cards. I've found that some of the Intel internal cards get a bit funny with more than a few users and linksys ones don't like *certain* APs with WPA encryption. Our D-Links work fine (now we've spent 2 years getting the firmware and card driver combination sorted!)

[gwendes]

Yes - I have exactly the same problems logging on 30 laptops in the same room at the beginning of a lesson using Aruba wireless hardware..

 

No solution just yet. New wireless cards, drivers etc and yesterday there were some kids that hadn't completed the login in 50 minutes!

[webman]

gwendes: Is that 30 laptops connecting to one access point?

[alan-d]

We have the same problems when 30+ log in in one room. We are reconfiguring all our access points to use just the 3 channels and jigging them about a bit, more to satisfy the users that we are trying something to improve it.

 

We are under no illusions that it will work any better, but it shows we are trying

 

I've deliberately missed off increasing the number of laptops in the development plan for next year

[gwendes]

gwendes: Is that 30 laptops connecting to one access point?

 

Sort of - the Aruba is supposed to be intelligent. The building has 5 access points that are apparently capable of around 50 clients each. It is supposed to force traffic to others if it is busy. Each room has about 3-4 available but the houses across the road are starting to be picked up too.

 

I really hate wireless.

[eean]

Is it centally managed? Our d-links are supposed to be able to force a client to go to a different access point if one AP hits a certain number, but it's very crude and they sort it out amoungst themselves. As you'd expect, it just crashes the whole thing! So it remains switched off.

I suppose, it might just work if you had 2 or 3 APs all in exactly the same place e.g on the trolley but on 3 channels, working as one cluster. (But I doubt it!)

[plexer]

Why not use mac filtering on the WAP's to restrict which clients can connect to each WAP?

 

Ben

[gwendes]

Is it centally managed?

Yes

I suppose, it might just work if you had 2 or 3 APs all in exactly the same place e.g on the trolley but on 3 channels, working as one cluster. (But I doubt it!)

The access points are all over the school site - the switch can produce a site map showing perfect coverage. The signal strength is fine I just need something to point at where the problem is with a big red arrow!

 

Everyone knows that wireless networking works by magic anyway...

[bishopsgarthstockton]

Hi,

 

I setup a mobile classroom of 30 laptops last summer. the mobile classroom is used in 3 rooms, Humanities, Design and technology and English. The AP i use are 3com 802.11b/g/a, the laptops have been configured to use only the 802.11a as it is more fault tollerant. the 3 rooms have 3 AP each so thats 10 laptops per AP. I wont let the laptops be used any were alse in the school even if you can still pick up the point, this just simply cuts down the problem as you abvouisly start to lose signal strength.

 

Up to now it has worked really well, had a couple of odd problems such as user not been able to log on as domain not available etc. also its not a good idea to push out software using Group policy as when the kids come to log on during lesson this can as you would imaging cause a lot of problems and delays. My self and the IT coorinator manage the laptop booking. each lesson is about 50 minuts i think so we only allow for 3 back to back lessons of use.

 

its a pain in the ass when it comes to updating the laptops or sending out a new ghost image. If you are ghosting i would conect the machines using cat5.

[gwendes]

its a pain in the ass when it comes to updating the laptops or sending out a new ghost image. If you are ghosting i would conect the machines using cat5.

 

I know that pain! I can do about twelve at a time overlapping them but it is not fun... I'm creating a new image atm and the plan is to image the entire disk with an image on the second partition so hopefully no more cat5!

[bishopsgarthstockton]

each laptop has been individually setup to connect to a persific AP.

 

laptop 1 can connect to ENG001A, DT001A, HUM001A

laptop 2 can connect to ENG002A, DT002A, HUM002A

laptop 3 can connect to ENG003A, DT003A, HUM003A

laptop 4 can connect to ENG001A, DT001A, HUM001A

 

etc

 

this takes out the decision process for the laptop and no more than 10 will ever connect to a AP.

[gwendes]

each laptop has been individually setup to connect to a persific AP.

 

laptop 1 can connect to ENG001A, DT001A, HUM001A

laptop 2 can connect to ENG002A, DT002A, HUM002A

laptop 3 can connect to ENG003A, DT003A, HUM003A

laptop 4 can connect to ENG001A, DT001A, HUM001A

 

etc

 

this takes out the decision process for the laptop and no more than 10 will ever connect to a AP.

 

How have you done this?

[bishopsgarthstockton]

@ gwendes

 

i have setup each laptop manually with only 3 ssid. you can how ever with 3com add 10 laptops wireless MAC addresses to the allow list on the AP.

 

another much more simple method is to use RADIUS but im not sure how to set it up. pluss i think you have to buy additional software for the server.

[maniac]

Hmmm, lots of people with different experiences.

 

The main problem for us is the laptops are intended for use potentially anywhere in the school building, so having dedecated access points just for these laptops is not very workable, as they would need to be school wide, and also having the laptops set to only connect to specific APs would be a nitemare, as theres 26 access points on site, and again the laptops could potentially be used anywhere on the school site.

 

The access points are all set to auto select channels, so they shouldn't overlap, although on the agenda for next week is manually setting the channels to space them apart as much as possible.

 

In response to eean -

The test on that was was we set 5 laptops logging on in the same area at exactly the same time, and yes it does cause problems. They will log on eventually, but it takes nearly 7 - 10 minutes for this to happen. An average desktop machine on our system will log on in approximately 25 seconds.

And nice ideas on the managed wireless network, we had already thought of this and we know it is the ultimate solution, except this is way out of our affordability. The existing wireless system was installed by myself, and it does work well, just not with lots of laptops in one space.

I will have a look and see what wireless adapter the laptops have in them, they are HP laptops and don't get me wrong, on their own, or with a few in the room they work very well. If they are intel cards, I think I've got enough spare 3com PCMCIA cards to try in them and see if that improves things.

[bishopsgarthstockton]

@ maniac

 

do the laptops have to connect any were in the school? can you not control where they can and can not?

 

your situatin sounds like a right nightmare

 

its intresting to see why 5 laptops would take so long to logon. it sounds as if cant decide which AP to connect to

 

laptop 1 hey im going to conect to this AP

laptop 2 hey im connecting to this one, get your own

laptop 1 you bully

 

7 min later....

 

laptop 1 aaaahaa! found one My precious :twisted:

[bishopsgarthstockton]

are the drivers and AP firmware up to date?

[alan-d]

We have a similar situation to manic only with 41 AP and 200 laptops - and yes they still want to move them from one end of the school to the other

 

We've managed to get the users to stagger logins which helps a lot.

[bishopsgarthstockton]

alan-d

 

200 laptops, how many of them are mobile classroom and how many are staff?

[projector1]

alan_d only 200 laptops?

 

 

have you looked at the logs files on the AP's for anything that may help diagnose the issue.

 

Do you have any other make AP that you could test around 8 machines on to see if the current AP is the problem.

 

we have around 80 teacher laptops that are wireless. Also we an area where theie are 18 laptops that have an AP and it is very stable

 

(wireless technology has along way to go before it can be fully relied on)

[bishopsgarthstockton]

too many access point in one area can cause problems

[Quackers]

We have 3 Laptop trollys. We have DLink 2100AP all over the school and that communicate with them. Most i have seen accessing 1 point was 58 laptops and the pupils did not complain of running slow or anything.

 

We did have problems at first with slow and freezing, but redirecting ONLY My Documents and Favorites folder stopped all those problems. The appdata over wireless was killing it. I think they want more trollys, all three are always in use.

[Quackers]

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