Wireless and laptop trolleys
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!