Dell Truemobile - how useful??

[Jim Carter]

On 2 May 2002, Aristotle wrote:
> I am about to get a Dell Inspiron 8200 with an internal wireless LAN
> card.  What can I do with it?  So far I seem to be seeing bad reports
> all over regarding range.  Should I just keep the wireless LAN card as
> some sort of backup or short range blue-tooth kind utility?  I was
> hoping I could get involved in a community based wireless LAN.

The Inspiron 8100 (I assume 8200 is similar) has the two internal antennas
in or near the speakers, and I notice a 3-4 dB signal drop comparing on a
wood table vs. on my lap.  Iron tables: put a book under it.  I wish they
could have run the wires into the lid :-)

I've used my Dell TrueMobile 1150 card with a Cisco-Aironet access point
(don't know the model) at 100 meter range with decent signal strength.
This was outdoors with a clear line-of-sight.  There were competing
outdoor AP's with less than optimal frequency selection, and the result
might have been even better if they would shut up.  If I read the spectrum
splatter right, neighboring AP's should be separated by 3 or more channel
numbers; 2 is pushing it.

I haven't played with my transmitter signal strength.  Obviously that's
important for long range.

In my house, I'm having interoperability problems with a Linksys WDT11;
currently the finger of blame points at Linksys (Intersil firmware), not
sending MAC level ack packets when it should.  This is under Linux.  With
the WinXP driver it works fine.  Another person is also missing acks in a
different circumstance, but nobody else is reporting exactly my problem.

In the house, antenna placement is important.  When a file cabinet is
between the gateway and the laptop, signal strength suffers.  My ideal
system would be either a regular AP or a USB wireless NIC, placed up high
for a good line of sight.  An antenna sticking out the back of the gateway
box is far from ideal.  But there's no Linux driver (yet) for USB wireless.

I don't know about residential construction in Australia, but plaster over
metal mesh is not kind to signals, and neither is thick concrete.
Plasterboard over termite food (wood) transmits signals with no problem.

> What will I need to participate in a community based LAN - say spread
> over a few suburbs?

I don't know how big a suburb might be, but if I were designing an AU-style
community LAN, I would have overlapping individual cells each with one AP
and a wired (DSL) egress path to the Internet.  I can't give any advice on
realtime roaming between cells, e.g. in a car, but I imagine most of the
usage would be from homes.  Neighboring cells should coordinate so their
DHCP gives out addresses in disjoint ranges.  You would have to do research
with the equipment recommended by your organization, to estimate the needed
cell spacing and the signal loss through house walls.  If the AP's could be
outdoors, you would win.

In the US, small ISPs are charged US$500/month per 1 Mbit/sec (possibly the
number is a year or two out of date), and if particular DSL lines had
consistently high data rates, questions might be asked. It would be a good
idea to nail down the fair usage issues with your ISP before they figure
out what you're doing and pull your plug.

James F. Carter          Voice 310 825 2897    FAX 310 206 6673
UCLA-Mathnet;  6115 MSA; 405 Hilgard Ave.; Los Angeles, CA, USA  90095-1555
Email: jimc at math.ucla.edu    http://www.math.ucla.edu/~jimc (q.v. for PGP key)