IEEE 802.11 wireless LAN WLAN

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IEEE 802.11 wireless LAN (WLAN)
By Robert Bolles
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802.11

• The IEEE 802 committee approved the 802.11
  standard for wireless LANs in 1997
• The standard has different data rates of either 1
  Mbps or 2 Mbps and operates in 2.4 GHz band
  intended for low-power unlicensed use by the FCC
• 802.11 allows for two different incompatible
  methods of encoding, FHSS and DSSS.
• FHSS (Frequency Hopping Spread Spectrum) spreads
  the conversation across 75 one-MHz sub channels,
  continually skipping between them.
• DSSS (Direct Sequence Spread Spectrum) breaks the
  band into 14 overlapping 22-MHz channels and uses
  one at a time.
• The 802.11 standard also allows for Wired
  Equivalent Privacy encryption at the MAC (Media
  Access Control) layer.

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Wireless LAN Mobility

• One of the greatest benefits of wireless LANs is
  mobility
• Network users can move about freely and access
  WLANs from almost anywhere
• Mobile IP is used in the IEEE 802.11 protocol to
  help achieve wireless LAN mobility

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Mobile IP

• Mobile IP works at the network layer and works
  with IP version 4
• With mobile IP, the IP address of a mobile
  computer does not change when it moves from its
  home network to a foreign network
• A forwarding routine is used keep connections
  between the mobile node and the network

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Configurations of a Wireless Network

• In the IEEE 802.11 standard for wireless LANs,
  there are two different ways to configure a
  network
• ad-hoc
• infrastructure

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Ad-Hoc Configuration

• The ad-hoc configuration allows individual nodes
  to participate in a peer-to-peer network
• In the ad-hoc network, there is no structure to
  the network there are no fixed points, and
  usually every node is able to communicate with
  every other node
• A meeting where employees bring laptop computers
  together to communicate and share information is
  an example of an ad-hoc configuration
• The spokesman election algorithm is utilized to
  have one machine as the master of the network and
  the others being slaves

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Infrastructure Configuration

• This configuration uses fixed network access
  points with which mobile computers can
  communicate
• These network access points are sometimes
  connected to landlines to extend the WLAN's
  capability by connecting wireless nodes to other
  wired nodes

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Limitations of 802.11

• One major problem with 802.11 equipment is its
  slow speed of 2 Mbps compared to wired networks
• Another problem is the incompatibility between
  FHSS and DSSS equipment
• The limitations associated with the standard led
  to variations of the 802.11 protocol

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802.11a and 802.11b

• In 1998, the IEEE introduced two variations of
  the 802.11 protocol
• IEEE 802.11a protocol operates in the 5GHz band
  and reaches data rates of 54Mbits/sec using DSSS
  (direct sequence spread spectrum modulation)
• IEEE 802.11b protocol operates in the 2.4GHz band
  and reaches data rates of up to 11Mbits/sec using
  OFDM (Orthogonal Frequency Division Multiplexing)

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Choosing 802.11a or 802.11b technology for your
WLAN

• Most of the WLANs implemented today comply with
  802.11b. However, 802.11a equipment is now
  available so both are viable solutions to
  implementing a WLAN
• There are considerations to take in to account
  when deciding whether to build a 802.11a or
  802.11b WLAN
• Although 11a WLANs do give a much higher
  bandwidth than 11b WLANs, the higher operating
  frequency of 11a equates to a shorter range
  compared to 11b
• This means more access points are required to
  cover a large size building using a 802.11a WLAN
  than are required using a 802.11b WLAN

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Considerations for using 802.11a

• If there is a need for a high bandwidth then
  802.11a is a better choice over 802.11b. One of
  the main reasons for choosing 802.11a is the need
  to support applications that need a large
  bandwidth like video, voice, and large images and
  files. 802.11b probably won't be able to keep up
  for these types of applications
• There is a substantial amount of interference
  that is present within the 2.4 GHz band. The use
  of 2.4 GHz cell phones and Bluetooth devices can
  crowd the radio spectrum used by a 802.11b WLAN
  and decrease the performance the WLAN. Using a
  802.11a WLAN operating in the 5 GHz band will
  keep away from this interference.
• Places like computer labs and airports need to
  support a large number of users in a specific
  area connecting to the same access point and
  sharing the available bandwidth. Using 802.11a
  will manage a higher number of users by giving a
  greater bandwidth

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Considerations for using 802.11b

• For large buildings 802.11b will give the most
  cost efficient WLAN due to its requirements for
  fewer access points.
• If you already have a significant investment in
  802.11b equipment then you may want to keep using
  it. There are relatively high costs with
  changing from a large 802.11b system to 802.11a
  system
• If there are only a few users that will connect
  to the WLAN then 802.11b will meet bandwidth
  requirements. This is because there are fewer
  users competing for each access point's total
  bandwidth. A 802.11a WLAN would just be overkill
  unless there is a need for high performance per
  user

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Backward Compatibility

• The IEEE 802.11a and IEEE 802.11b are not
  backward compatible
• This means that a user connected to a 802.11b
  WLAN could not connect to a 802.11a WLAN
• The reason for this is the different radio
  frequency and modulation types of 802.11a and
  802.11b causes them to not interoperate
• To solve this problem Intersil Corp. has
  developed a client card that uses a chip that can
  handle a combination of 802.11a, and 11b
  technology
• Such a dual-band radio would allow a laptop user
  to connect to the widely implemented 802.11b
  WLANs and the more recent 802.11a WLANs

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Alternative to dual band client card

• Some companies may simply handle a mix of 11b and
  11a nets in access points, rather than on client
  computers
• Several wireless LAN vendors plan to build access
  points that can hold two interface cards
• Users can put a combination of 11a and 11b cards
  into each access point to support users with
  different client cards

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Security for WLANs

• Wireless access points are like small radio
  stations
• There are some free programs available on the
  Internet that can tune into these network devices
  and obtain useful information about them. One
  program available is Net Stumbler
• Net Stumbler will give information about WLANs
  like
• If WEP encryption (Wired Equivalent
  Privacy) is turned on or off
• The MAC address of the AP
• The manufacturer of the AP
• The SSID (Service Set Identifier) or
  network name
• The channel the AP is using

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Net Stumbler

• You dont have to worry about tools like this if
  you have a secure WLAN.
• However, Alan Rothberg used Net Stumbler on is
  laptop with a wirless network card, and while
  driving around in his car in Charlotte, N.C he
  found that no more then 17 of the access points
  he found had WEP enabled.
• WEP is not unbreakable but it does increase a
  hackers work in trying to break into a WLAN
• Also, using WEP is overhead reducing bandwidth by
  1 Mbps

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Important information found on WLANs in Charlotte
NC

• In many of the APs he found, the APs were named
  in a way that gave company names or personal
  names that were easily traceable
• Many of the AP names were the same names given by
  the manufacturer. This gives a hacker important
  information that can be used to break into the
  WLAN
• Many of the APs were inexpensive and these
  inexpensive APs do not have the management
  features that help in securing a WLAN

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Map of wireless access points in the Charlotte,
N.C.
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Security Tips for WLANs

• Know what you will use your WLAN for
• What kind of security model will you need? What
  would be the consequences if your WLAN were
  broken into?
• Use tools like a VPN (Virtual Private Network) on
  your access point or put a firewall between your
  access point and your network
• Use your APs built in security features like WEP
• If high security is needed, invest in a more
  expensive AP that has additional security
  features
• Place APs in the middle of buildings away from
  windows
• Dont use descriptive names for your WLAN
• Do a site survey and find out where your coverage
  areas are

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Works Sited

• http//www.oreillynet.com/pub/a/wireless/2002/03/2
  9/wardriver.html?page1
• http//www.80211-planet.com/columns/article/0,4000
  ,1781_961181,00.html
• http//www.oreillynet.com/pub/a/wireless/2001/03/0
  2/802.11b_facts.html
• http//computer.org/students/looking/summer97/ieee
  802.htm
• Cox, John. Proposal could ease wireless
  upgrades. Network World 3 Sep. 2001 17.
• Dorman, Andy. Up Where the Air Is Clear?
  Network Magazine Oct. 2001 18.