[lug] 802.11b wireless

[Nate Duehr]

"J. Wayde Allen" wrote:
> 
> I'm setting up for a conference and there are hard wired ethernet
> connections in the conference room connected to a dhcd server.  I've also
> got an 802.11b pcmcia wireless card available.  I'm thinking that it
> should be possible to hook this card into the network in order to create a
> wireless segment for my meeting.  I'm just not too certain what I need to
> do to pull this off?
> 
> - Wayde
>   (wallen at lug.boulder.co.us)

Hi Wayde... 

Looks like everyone's already got you going on the right track, but
since I've done a fair share of this stuff, a couple of notes...

Someone mentioned the Lucent cards and some other cards can't talk to
each other always in Ad-Hoc mode.  There are two distinct versions of
Ad-Hoc... Lucent started it, and the original would only go 2Mb/s.  The
"IEEE Ad-Hoc" mode will do 11Mb and is the one almost all vendors now
support.  In addition, if your Lucent WaveLAN card says "IEEE" on it, or
is an "Orinoco" card, a flash update will bring it up to speed with the
rest of the world.  Very old Lucent cards cannot be updated to do the
new Ad-Hoc mode.  Most (the vast majority) can.  Once you teach your
Lucent new tricks, you CAN select which type of Ad-Hoc mode in the
settings for the kernel module... see the README stuff in the module
itself or in the docs, I forget where... (GRIN).

The cards I have with the Prism2 chipset are a pain in the butt.  :-) 
That's all I'll say about those.  Well, to be more specific, the kernel
modules don't move well from one version of the kernel to the next and
there seems to be continuous releases of the module to make it work...
and of course it's always behind where I want to be on the kernel. 
(GRIN)  There are some patches out there that will supposedly put a
Prism II card into "true" AccessPoint mode, but I got frustrated and
forgot about it.

Power saving features on all cards are disabled in Ad-Hoc mode, due to
the way the mode works.  If you're going for long life on the laptop
battery, get a real Access Point so the AP can manage your card's power
and you can pulse on and off.

I have a machine downstairs that acts as a router between wired and
wireless.  If you buy a $20 ISA to PCMCIA adapter on Ebay and then stuff
it in an old machine that still has an ISA slot (GRIN) you can make a
decent little Ad-Hoc access point. 

If you're using the Lucent cards, you can enable the (broken) WEP
encryption without difficulty in Ad-Hoc mode if it makes you sleep
better.  :-)

If you have Apple AirPort cards, they'll do Ad-Hoc mode just fine under
Mac OS 9 or Mac OS X too.  They're basically Lucent cards.  They talk
nicely to a Linux-based Ad-Hoc router.

If you have a broken AirPort access point that's out of warranty you can
steal the Orinoco Silver card from inside it and put it in your laptop
or the "router" machine, no problem.  (GRIN... and just guess how I
found this out.  My AirPort blew some power supply capacitors and other
stuff appears to be wrong with it electronically -- it makes neat
noises, but doesn't act much like an access point... and I've read a lot
of horror stories about these things frying themselves... no fan, no
slots for heat... DUH.)  Of course, the silver card is only 40-bit
encryption.

The Prism II chipset cards stuffed in a Windows machine will connect in
IEEE Ad-Hoc mode to the linux router fine.  Yep this is where my Prism
II card went... get it away from the Linux machines... it's annoying me
there.  Heh.

Running dhcpd on the router works well.  Running iptables on the thing
also does a nice job of creating a stateful firewall for the machines
behind it.  Lucent cards can NOT handle bridging mode well, nor can you
put them in promiscous mode.  They just don't do it.  If you're planning
on going "war driving" get Prism II cards or Cisco stuff from what I've
read.  Personally I don't have the time...

The Linksys mixed wired and wireless router thing just plain sucks. 
Some of you remember probably that I do a lot with VoIP stuff and ham
radio -- we have never had a happy person who bought one of these and
stuck their VoIP stuff behind it either on the wired side or the
wireless side.  Linksys appears to have tied the interrupt line from the
microprocessor on the wireless section to the microprocessor in the
wired section (not confirmed, but the theory matches the symptoms) and
whenever wireless traffic goes up, the firewall, port-forwarding, and
other functions go to hell and packet loss goes sky high through them. 
Their other stuff works great, but I'd stay away from their mixed
wired/wireless router thing... it's bad news.  There's a rumour that a
"REV 2" version of this thing came out to fix the hardware problems, but
I haven't seen one nor talked to anyone in the 350+ person group that's
playing with wireless toys.  (GRIN)

If you're going to put a wireless card in a desktop machine, don't
bother with the PLX cards (special PCMCIA bridges that only understand
how to talk to the wireless PCMCIA cards) in either Windows or Linux. 
Just get a cheap PCI to PCMCIA bridge card and drive slot adapter on
Ebay, again... about $20.  The PLX cards run about $100 and do nothing
more than make the machine think it has a PCMCIA slot.  If you use a
real PCMCIA adapter, you end up with a real extra PCMCIA slot that can
be used for other useful things like PCMCIA SCSI interfaces for a
portable drive, a scanner, whatever... get the PLX and all you can put
in it is that vendor's wireless card.  Don't bother with them.  :-)

For the "instant gratification" thing, check out Micro Center if you can
handle the drive to I-225 and Tamarac.  They had about five different
models of Access Point in there last time I was in there, including the
Linksys, the SMC, and three others I don't remember.  They didn't have
the Lucent Residential Gateway, which I've heard good things about.

One other item... if you're into ever extending the reach of your
802.11b network... get Lucent cards.  They're the only ones I've seen
yet with the external antenna connection on them with a good connector. 
The pigtails go from their connector on the card to a communications
industry standard "N" connector which can be connected to hardline (for
towers), or really good quality coax cable (don't buy cheap stuff for
2.4 Ghz... you'll lose everything you put into it in the coax and never
make it to the antenna).  A friend is shooting 802.11b up to a mountain
top with "barbeque grill" dishes for 2.4 Ghz and it works great... he
has radio gear up there that needs TCP/IP connectivity.  Yes... it's an
FCC Part 15 device and must neither create any interference and must
accept all interference it receives... but if you plan carefully you can
shoot 802.11b for miles.  There are power limits, please don't just run
out and buy an RF amplifier without doing the calculations for EIRP --
or you'll just mess up the band for the rest of us.  

Oh and speaking of RF power... the Cisco cards are the only ones I've
seen that allow someone that knows something about RF to set the power
level of the card in steps.  In a building environment where particular
access points and machines may "overlap" and interfere with each other,
the Cisco stuff might save the bacon if you can get the power levels set
just right to cover without interference.

Ummm... and finally... on Lucent cards, Channels 1, 6 and 11 are the
only three where the spread-spectrum frequency ranges do NOT overlap
somewhat.  So if you have two access points in a building, put them at
opposite ends of the channel range on just about any channel, but if you
have three, make sure you use 1, 6, and 11... if you have more than
three, you're going to have to get creative and try to make sure the two
on the same channel or on overlapping sections of the band don't
interfere with each other -- it won't be perfect, but you can make it
happier by good RF planning... you can find more info on the web on this
stuff.

I'm working on a machine to go the OTHER way right now... wireless LAN
to wired ethernet.  Should work, but the wireless side is DHCP set... so
I'm going to try to build a script that sees if the IP changes every
minute or two and rebuilds the iptables rules to NAT from private side
to DHCP public side addresses.  Odd setup, but I need it.  I'll let
everyone know how it turns out.   This one could go really easy, or
could annoy the heck out of me for days of tinkering.

:-)

Oh and finally, for licensed hams out there... someone pointed out to me
that the ham 2.4 Ghz band extends up into the bottom portion (first
three channels) of the 802.11b spectrum.  Now I'm not sure it's a real
good idea, and you'd have to stuff your callsign into the thing somehow
or morse-code (CW) ID's ... but there might be a way for a licensed
person to run 802.11b at the full legal limit for Amateurs in the 2.4
Ghz band for power... 

Of course, using it for commercial use or turning on the encryption
would be illegal under ham rules... heh heh... so it'd be kinda
useless.  But these are the things you research when you're bored and
just don't want to e-mail out any more resumes' one afternoon...  GRIN. 
Heck even transmit profanity over it, and you could lose your license...
just have a friend send you an e-mail cussing you out.  Heh heh.

Okay now seriously, this is just a joke idea... and not a very good one
at that... but technically it might be able to be done.  Finding a
spectrally pure amplifier at that high a power level for spread-spectrum
DSSS 2.4 Ghz signals?  Good luck.

Nate, nate at natetech.com