Thursday, September 16, 2010

Too much wireless is a new limitation

The wireless itself is holding up very well. The infrastructure itself is over dimensioned for the amount of traffic and devices we expected to connect to the wireless. Though we see a lot of very happy people, but we also hear complaints.

The people using Apple OSX and Windows are typically smiling. Luckily means that most of the people are happy. We encourage these users to saturate the available bandwidth as we have plenty to spend. We don't saturate our first 10Gbit line to the internet by a long shot, so don't hesitate to do actual work on our infrastructure while eating a sandwich.

The Linux people might have a different experience. During the conference different people noticed dropped connections or that they couldn't connect to the access points. Different people were busy with it and we have a sad conclusion to tell that the limitation is in the Linux kernel itself (which took some time to find).

In short, there are too many Wireless access-points in the venue and in its vicinity. In slightly more detail we tracked down three different problems:
- Driver issues: Intel drivers typically have issues with the amount of access points. Some of the people tried different drivers, like the midwife drivers.
- wpa_suppicants: You can see memory overflow errors in the log messages. using eduroam will be difficult.
- kernel limitations: there is a buffer with a limit of 2^16 bytes to store the essential wireless information. This is hardest problem to fix.

Background information about the problem:

What we did from the infrastructure side: the wireless system serves a bunch of SSIDs for the BiGGrid user day and the EGI meeting side by side. To overcome the wireless problems we removed the lesser used SSIDs to lower the entries in the memory for the drivers and kernels. We also dimmed down the radio antenna output to a minimal, so that you won't be able to list the APs from the other end of the building. If the problems persist we'll probably going to switch of APs as a last resort.

The lessons learned are that too much wireless networking doesn't always benefit the user experience.

(Read all about the challenge of setting up the conference wireless in Oscar's earlier post here)

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