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Linux and Wireless

Presented by Reed Gregory on June 20, 2002

Table of Contents


1. Introduction


1.1. So Many Standards

What is Wireless? Wireless Ethernet is ethernet usually transfered over
radio ways at certain frequencies. It provides a wireless high speed
ethernet connection. It can be very useful for people who have laptops or
other mobile devices that need an internet connection. There are currently
many different Wireless devices with many standards. Some of the standards
include 802.11, 802.11-DS, 802.11-b, 802.11-a, HiperLan, HiperLan II,
OpenAir, HomeRF / SWAP, and BlueTooth. We will focus on 802.11-b, 802.11-a,
and a little BlueTooth.


1.1.3. BlueTooth

BlueTooth is not Wireless LAN. It is a cable replacement technology
mostly developed and promoted by Ericsson with the help of Intel, offering
point to point links and no native support for IP. It is much like a
Wireless USB idea. I only mention it here because of the confusion that
BlueTooth is some kind of Wireless LAN.


2. 802.11-b Vocabulary

  1. ESSID The ESSID is used to
    identify cells which are part of the same virtual
    network.
    As opposed to the NWID which defines a single cell,
    the ESSID defines a group of cell connected via
    repeaters or infrastructure, where the user may
    roam. With some card, you may disable the ESSID
    checking (ESSID promiscuous) with off or any (and
    on to reenable it).
  2. NWID As all adjacent wireless networks share the same medium, this parameter is used
    to differenciate them (create logical colocated
    networks) and identify nodes belonguing to the same
    cell. With some card, you may disable the Network
    ID checking (NWID promiscuous) with off (and on to
    reenable it).
  3. MODE The mode can be
    1. Ad-hoc
      (network composed of only one cell and without
      Access Point)
    2. Managed (network composed of many
      cells, with roaming or with an Access Point)
    3. Master (the node is the synchronisation master or act as an Access Point)
    4. Repeater (the node forward
      packets on the air)
    5. Secondary (the node act as a
      backup master/repeater)
    6. Auto
  4. Access Point An access point is just a device that acts as a path from your wireless device to a wired network. Many Access points can be attached together to act as repeaters or even bridged together. But on down the line, an Access Point is in charge of trasferring the wireless signal to a wired network. It acts just like a hub.
  5. Bandwidth Rate The rate is just a measure of the speed of the connection. In 802.11-b these range from 1 to 11 Mb/s. The nice thing about these is that if your signal is not strong enough for one, it will drop down to the next highest signal. This will auto-negociate to the best rate possible and keep checking at some interval.


3. Wireless Encryption

The encryption in the 802.11 specification is a RC 4 Algorithm. Much has
been said about the the WEP or Wired Equivalent Privacy key having some
serious security flaws. The key is easily cracked but only after long
periods of time when data can be recieved and then analyzed. The idea
of WEP, however was just to provide a privy equivalent to wired ethernet.
Wired ethernet has privacy because someone would need to get into a
building or get to a wired port. The wireless web is just supposed to
provide a deterent. A better solution to having people not access you
wireless network is to have you AP only talk to specified MAC addresses or
unique wireless cards of authorized users.

802.11-b supports both 64bit and 128bit encryption keys. The GT LAWN
uses ta 64 bit setup. Sometimes you may hear about 40bit or 104bit
encryption. These are the same as 64/128 but that some people refer to 24
of the bits as a different part.


4. Wireless and Linux


4.1. Drivers


4.1.1. Pcmcia

First you need pcmcia support to use the PCCard devices. Most people
would only run wireless on laptops because the speed of wired ports is
much better for desktops. I will not go over how to get pcmcia support
in Linux. That is beyond the scope of this document. Most people would
say to use the kernel pcmcia support and use the scripts from the
pcmcia-cs project.


4.1.2. Wireless Cards

The wireless card drivers are either found in the kernel or in a
seperate package. There are a few packages available including pcmcia-cs
and wg-lan. The file that takes care of assigning which driver to which
card is /etc/pcmcia/config.


4.2. Testing

Once you have everything setup you can try to insert the Wirless card and
look at your logs specifically /var/log/messages for information on your
wireless setup. If you do not see anything in those logs, you might want
to make sure pcmcia service is started. The following is a portion of my
logs pertaining to my wireless card.

Jun 18 15:40:09 silver-bullet cardmgr[1005]: socket 2: Lucent Technologies WaveLAN/IEEE Adapter
Jun 18 15:40:09 silver-bullet cardmgr[1005]: executing: 'modprobe orinoco_cs'
Jun 18 15:40:09 silver-bullet cardmgr[1005]: executing: './network start eth1'
Jun 18 15:40:10 silver-bullet /etc/hotplug/net.agent: invoke ifup eth1


4.3. Wireless Tools

The Wireless Tools is a set of tools allowing to manipulate the Wireless
Extensions. They use a textual interface and are rather crude, but aim to
support the full Wireless Extension.


iwconfig – manipulate the basic wireless parameters
iwlist – (formerly part of iwspy) allow to list addresses, frequencies, bit-rates
iwspy – allow to get per node link quality
iwpriv – allow to manipulate the Wireless Extensions specific to a driver (private)

The latest wireless tools package can be found at
http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/Tools.html


4.4. Schemes

Schemes are nice for when you have multiple wireless networks you connect
to at different times. For instance you could have one for the LAWN and one
for your work/room. This way you can just give easy commands to change
the schemes. You can just use the cardctl command to change schemes.

cardctl scheme scheme-name

For scheme support to work, you need to have support for it in 2 files,
networks.opts and wireless.opts which are located in
/etc/pcmcia/.


4.4.1. network.opts

Click here to download network.opts.

# Network adapter configuration
#
# The address format is "scheme,socket,instance,hwaddr".
#
# Note: the "network address" here is NOT the same as the IP address.
# See the Networking HOWTO.In short, the network address is the IP
# address masked by the netmask.
#
case "$ADDRESS" in

lawn,*,*,*)

DHCP="y"

;;

room,*,*,*)

DHCP="y"

;;

esac


4.4.2. wireless.opts

Click here to download wireless.opts.

Wireless LAN adapter configuration
#

case "$ADDRESS" in

# Lawn stuff
lawn,*,*,*)

INFO="LAWN"

ESSID="GTwireless"

MODE="Managed"

KEY="xxxxxxxxxx"

;;

#room stuff
room,*,*,*)

INFO="apartment room"

ESSID="ssaw318"

MODE="Ad-Hoc"

KEY="off"

;;


# Generic example (decribe all possible settings)
#*,*,*,*)
#INFO="Fill with your own settings..."
## ESSID (extended network name) : My Network, any
#ESSID=""
## NWID/Domain (cell identifier) : 89AB, 100, off
#NWID=""
## Operation mode : Ad-Hoc, Managed, Master, Repeater, Secondary,
##auto
#MODE=""
## Frequency or channel : 1, 2, 3 (channel) ; 2.422G, 2.46G
## (frequency)
#FREQ=""
#CHANNEL=""
## Sensitivity (cell size + roaming speed) : 1, 2, 3 ; -70 (dBm)
#SENS=""
## Bit rate : auto, 1M, 11M
#RATE=""
## Encryption key : 4567-89AB-CD, s:password
#KEY=""
## RTS threshold : off, 500
#RTS=""
## Fragmentation threshold : off, 1000
#FRAG=""
## Other iwconfig parameters : power off, ap 01:23:45:67:89:AB
#IWCONFIG=""
## iwspy parameters : + 01:23:45:67:89:AB
#IWSPY=""
## iwpriv parameters : set_port 2, set_histo 50 60
#IWPRIV=""
#;;
esac


5. GT LAWN

The LAWN is the Georgia Tech Local Area Wireless Network. It is a on
going project to provide wireless (802.11-b now) service in campus
buildings. The equipment is Lucent/ Agere wireless Access Points that
can easily be upgraded to 802.11-a. The LAWN works in the following way.
You need to get the WEP key that OIT uses for the LAWN from OIT. Then
once you have the card setup you need to insert the wireless card and
bring up the interface using dhcp. After that, just open a web browser
and sign-in to the LAWN. Now you are on the LAWN.


6. LAWN Coverage

The most up-to-date information on LAWN coverage can be found in the
OIT FAQ: http://faq.oit.gatech.edu/0256.html

Building Coverage
500 Tech Parkway Full
845 Marietta Street Full
A.French Building Full
Architecture Building Full
Manufacturing Research Center Full
Bookstore Mall CyberCafe Full
Carnegie Building Full
Centennial Research Building Full
Coliseum Annex Full
College of Computing Full
Georgia Center for Advanced Telecom Tech Full
Human Resources Full
Library Full
Rich Computing Center Full
Van Leer Building Full
Wardlaw Center Full
811 Marietta Street 2nd floor
Alumni House 1st floor
Baker Building 2nd floor and SE corner of 1st floor
Calculator 2nd floor only
ESM building Ground floor
Instruction Center 2nd floor only
King Facilities Building SW office area
Lyman Hall 3rd floor S
MRDC Varios Parts of 2nd and 3rd Floors
Pettit Building (MiRC) Room 102


7. Available Devices and Prices

These prices were taken from www.buy.com
just for an idea of what devices cost.


7.1. 802.11-b

Based on the 802.11 standard which was finalized in September of 1997,
this standard operates at the 2.4 Gigahertz Frequency at speeds of 1, 2,
5.5 and 11 Mb/s. The later 2 speeds were introduced with the 802.11-b
standard. There were only slight changes in the DS physical layer from
802.11. It is by far the most common standard in use today. The GT LAWN
runs on 802.11b.


7.2. 802.11-a

802.11-a was standardized before 802.11-b as the name implies. It is
just now starting to hit the market however. It is sometimes referred to
as 802.11 at 5 GHz. It offers speeds of 6, 12, and 24 Mb/s and optional
speeds of 9, 18, 36, 48, and 54 Mb/s.


8. Resources

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