[Wylug-discuss] School Pilot

[Paul Scorer]

Hi,

I write as a "wylugger" and Senior Lecturer from Innovation North (ex
School of Computing) at Leeds Metropolitan University, but I should make
clear that the views expressed here are my own.

First, I am delighted that a school is looking to run Linux! Good luck
with it.

However, I must advise caution when using wireless network access for a
large number of machines which are likely to require significant
simultaneous network traffic, and in particular during a network login.
We attempted to run a class with 25 portables in classrooms with two
(802.11a) access points in the room. Access was so slow that the
screen-saver cut in before login was complete: because authentication
was not complete, this could not be unlocked, and the only solution is
to forcibly switch off and start again. Even if successful, login was
taking 10 minutes or so.

The reason is obvious if you go through it: 802.11a (and 802.11g) offers
a gross bit rate of 54Mbps at best. Achieved gross *throughput* is
unlikely to exceed 25 Mbps for each AP. 25 machines implies a best
possible individual throughput to a single station of 1 Mbps. If
collisions, backoff, retransmissions, etc are included, 250 Kbps
throughput is a more likely figure for each work-station. This is to be
compared (in our environment) with 100 Mbps per station for wired
machines. Classroom teaching on wireless connected portables was not a
success.

This does not, however, deny the value of wireless access for the
"casual" user. Just don't use it in an environment where many people
need intensive network activity simultaneously. I fear that this may
represent a typical usage pattern in a school, just as it did for us.

HTH

PaulS