Wireless and laptop trolleys

[karlr]

How do you handle laptop trolleys and wireless connectivity?

 

We've had an ongoing issue with the performance of wireless connectivity when serving laptop clusters. This often manifests in extremely long logon times, missing group policy/drive mappings, and the network suddenly being unavailable just as the student is going to save the coursework they've been working on all lesson.

 

This typically only occured in one or two particilar rooms, so although on and off research was done on the issue, it wasn't priority one.

 

Now, over the easter break four of our laptop trolleys (15 laptops each) were reimaged with our shiny new Xp image created and deployed elsewhere at the end of last year. Unfortunately due to the age of the image, these laptops were now in need of many updates. So naturally, when the teacher has the students fire up 15 (or in some cases 30!) laptops in a room, they all start downloading a 100mb of updates all from the same poor AP, naturally crushing the wireless performance and any chance the students have of being productive. Considering how limited the bandwidth of even a perfect A/G WLAN is and the number of laptops in use, it's becoming clear that we will need to consider disabling automatic updates for our laptop clusters (or give them a subset of updates in WSUS). In this case we'd have to either perform some sort of scheduled maintenance on the laptops by hooking them up to ethernet, or leave them as they are (something I wouldn't be overly happy with, especially not for our Windows 7 laptop cluster).

 

Now, in terms of the wireless configuration we've spent some time researching basic best practices as well as trying to understand our particular APs (HP ProCurve 530). The existing configuration that was in place seemed to be a mix and match of b/g/a, with channels set to same in neighboring rooms and power reduced all the way down to 2dBm in some cases.

 

What we're looking at now is running an 802.11a (5 GHz) only network, which in theory should prevent issues from bluetooth mobile phones etc, and allow for the use of more channels (augmented by the shorter range). Initial tests with inSSIDer indicate that we can get a strong signal (as good as -41 RSSI, which I understand might be TOO strong) from each AP in each respective room. Rooms typically get a very poor signal from the APs in other room (apart from two rooms that are seperated by a false wall). Following advice, we set the APs to auto channel selection, however they all seem to have chosen channel 38 despite being brought up one at a time. Presumably this is because the individual signals are not reaching the other APs, or isn't strong enough to warrant a different channel?

 

Assuming the wireless works just fine, we now come to the problem that 802.11a can only support a maximum data rate 54mbit (20~mbit of actual throughput). When we get teachers doubling up on trolleys and handing out 30 laptops in a classroom, this obviously doesn't leave much bandwidth to share, especially in this age of whizz-bang VLEs, interactive education, and the Internet. I was optimistic to think that the 802.11a WLAN might have enough reach such that we could load balance laptops across multiple APs, but sadly this doesn't seem to be practical at all due to the range limitations (no doubt g would fare better, but then we get the problem of 2.4GHz interference and the fact that we have 5 APs in five adjacent rooms). We're also thinking about the option of roaming profiles for students (or at least making a more robust mandatory profile) which could potentially take us back to square one as far as logon times go.

 

So how do the rest of you in the precarious situation of having laptop trolleys cope with wireless connectivity and performance? Without spending any money of course...that's naturally all reserved for replacing the shredded power cables for the laptop PSUs and the various missing/destroyed keyboard keys. It's all just normal wear and tear though!

[pcstru]

We suffer some of the same problems. My intention is to mount a WAP on each trolley and configure the laptops to use that. Teachers will have to plug the WAP to a socket but ultimately it gives us the control we need to provision enough bandwidth for each trolley without having to mount up enough permanent AP's to cover all areas. Well ... that's the plan - no doubt someone will now tell me why it won't work!

[thepineapplehead]

Well ... that's the plan - no doubt someone will now tell me why it won't work!

 

because you're relying on teachers to plug things in

 

Even with two network sockets labelled for laptops, instructions printed on the trolleys, and physically showing staff how to plug it in, you'll get teachers who don't plug in the power cable, network cable, or both. Or plug them in the wrong sockets. Or forget to switch the power on.

[nicklec]

Basically stop using consumer APs, more radios(enterprise APs have multiple) 802.1n = better performance; common sense really - 'physicalising' the problem by using an AP per trolley doesn't really help, what channels are you going to use - what if the trolleys are in range of each other?

[pcstru]

Basically stop using consumer APs, more radios(enterprise APs have multiple) 802.1n = better performance; common sense really - 'physicalising' the problem by using an AP per trolley doesn't really help, what channels are you going to use - what if the trolleys are in range of each other?

 

We don't use consumer AP's. Our current kit is unmanaged CISCO AP's and we will be rolling out MERU AP's over the summer. I was under the impression that the MERU controller would handle the channel allocation and cope with AP's springing up out of the ether. The problem for us is that we operate on a huge site and ensuring that trollies can be used anywhere with fixed AP's necessarily involves putting in a ton of overcapacity that 95% of the time will be unused. It seems to make a lot of sense to try and deliver that capacity where it is needed, when it is needed rather than spend an extra £20K + on access points.

[pcstru]

because you're relying on teachers to plug things in

 

Even with two network sockets labelled for laptops, instructions printed on the trolleys, and physically showing staff how to plug it in, you'll get teachers who don't plug in the power cable, network cable, or both. Or plug them in the wrong sockets. Or forget to switch the power on.

 

True enough!

[karlr]

because you're relying on teachers to plug things in

 

Even with two network sockets labelled for laptops, instructions printed on the trolleys, and physically showing staff how to plug it in, you'll get teachers who don't plug in the power cable, network cable, or both. Or plug them in the wrong sockets. Or forget to switch the power on.

 

I suggested a pie in the sky solution to my network manager the other day that involved sticking a cheap 16 port switch on the trolleys so that the laptops would be manageable over a wired connection when not in use... I then managed to kill my own suggestion by pointing out that teachers have enough trouble just plugging in the power cables!

[geraintpowell]

Hey there,

 

We use laptop trolleys that contain between 12 and 20 laptops each. we have 5 trolleys, used by certain departments and one general use trolley.

We have equipped each trolley with a wireless router. we dont get many problem with teachers not plugging them in, but sometimes they plug them in with plenty of excitement and break the data sockets, the general trolley is moved and plugged in by a technician.

 

I've found that the router is enough to provide a connection to 20 laptops, but any more than that and they start to become intermittent.

 

Another issue we get is that the trolley's power must be on with the trolley connected to the data line for about a minute before any laptops try to connect, otherwise they wont connect unless you restart all of the laptops, which is a nightmare for a teacher with a class full of kids.

[gjdb]

All our classrooms (30) have 1 to 3 Cisco Aironet 12xx AP (so our whole building has coverage), depending on the amount of laptop`s we expect to being used in that classroom.

If a classroom has 10 laptops, it gets one AP and if a classrooms has 30 laptops in a trolley it gets 3 AP`s, running on channel 1,6,11.

This setup is already running 5 years now, serving 150-175 laptops daily without any issues.

They get all the updates from our wsus server and running any program from our file server, including programs which needs to be installed.

They are even used for digital exams, which is installed from the network at first run and afterwards the exams are also downloaded (75mb à client).