WLANs
wireless access point (AP) instead of
an Ethernet switch.
• 802.11 prescribes collisionavoidance instead of collisiondetection
each client uses a wireless adapter to
gain through a wireless router or access
point.
What required to access Wlan?
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SSID: (the name of network)
broadcast: enabled, BEACON
Probe
after it the client is just in the network and for each
service it should have access by any possible means.
EBS (Extended Base Station)
associasion
security mode(TKIP,AES) should be the same on client
and AP
open access
security AEP: just shared key
Association
• open access
• association
• security AEP: just shared key
Security
• security mode(TKIP,AES) same on client
as AP
• security AEP: just shared key
• WAP – WAP2
• CSMA/CA
• Access points distributed coordination function
(DCF) called Carrier Sense Multiple Access with
Collision Avoidance (CSMA/CA).
• devices must sense the medium for energy (RF
stimulation above a certain threshold) and wait
until the medium is free before sending.
CSMA/CA
• An access point receives data from a client
station, sends an acknowledgement that
received.
• assuming a collision not occurred and prevents
a data retransmission by the client.
War driving
• "War driving" originally using a scanning device
to find cellular phone numbers to exploit.
• Now means a laptop and an 802.11b/g client
card looking for unsecured 802.11b/g system to
exploit.
Modulation
• 802.11a/g support up to 54 Mb/s
• The data rates of different wireless LAN
standards, are affected by Modulation.
• Direct Sequence Spread Spectrum (DSSS) ,
cheaper
• Orthogonal Frequency Division Multiplexing
(OFDM), faster.
• 802.11n 248 Mb/s (MIMO)
5Ghz vs. 2.4
• 5 GHz band less interference smaller antennas.
• higher frequency band slightly poorer range than
either 802.11b or g.
• Russia, do not permit the use of the 5 GHz
band.
• 2.4 Ghz being interfered by other devices.
• 802.11n uses multiple radios and antennae to
establish multiple streams.
Standardization organizations
• ITU-R regulates allocation of RF bands.
• IEEE specifies how RF is modulated to carry
information.
• Wi-Fi ensures that vendors make devices that
are interoperable.
• Applications surve site to show APs and the
technologies
• Examples(Cisco Aeronet , Wireshark)
• Also hardware devices APs available(Fluke)
• Verifying network configurations
• Finding locations with poor coverage in a WLAN
• Detecting causes of wireless interference
• Detecting unauthorized ("rogue") access points
Locationing
• With specialized antennas the direction
the transmission comes from can be
determined.
• AoA-locationing is used in old school
triangulation and radar systems.
Time of arrival locationing in GPS
Locationing
• Received signal strength RSS is
especially important in indoor
environments since GPS doesn’t reach
there.
WiFi vs. WiMax
• as most people think WiMax is merely a
more robust version of WiFi.
• both wireless broadband technologies
• But differ in the technical execution and
business case
WiFi vs. WiMax
• Some people describe the difference
between WiFi and WiMAX as analogous
difference between a cordless phone and
a mobile phone.
WiFi vs. WiMax
• Unlicensed frequencies are not allowed to
be as powerful as those operated with
licenses; less power less distance.
• The problem of everybody shouting at
once, even if it's surmountable in a
classroom, would be catastrophic in a
larger arena. Maybe.
WiFi vs. WiMax
• WiMax was to access the last line to the user as
an alternative to cable and DSL.
• WiFi was developed for laptops and computers
in a lan, but know they are used in different ways
by diff devices.
• WiMax is better when it is used between WiFi
nets, because it has more range and
bandwidth.54 Mb and 30 M indoor.WiMax 70
megabits, 112 km.10 mb and 2 km.Wimax more
bandwidth efficient.
WiFi vs. WiMax
• WiFi competing devices for the access to the AP,
most near most bandwidth and interrupting other
users who are farther.
• Wimax uses scheduling algorithm compete once
after that the client will be given a slot by the
base station. slot can enlarge and contract, but
other subscriers cannot use it.stable on over
load and over subscribtion.Algorithm allows
base station to control QoS by balancing the
time slot assignment among the applications
need of the suscriber stations.
WiFi vs. WiMax
• WiFi uses 2.4 usualy 2400Ghz to 2487Ghz, each
channel 22 but the intervals are 5.to the next higher
channel.
• 13, 11 and 14 Europe ,NA and JP.
• WiMax 10 to 66Ghz
• 2004 2 to 11GHz 802.16d (fixed Wimax and 2005
802.16e (mobile WiMax) used diff OFDM opposed to d
with 256 sub_carries.
• new 802.16e was developed with multiple antennas and
multiple inpit output.Full mobility support.because of low
frequency there are in building availability and improved
range,because of less signal antenution.
WiFi vs. WiMax
• Symmetrical bandwidth, many kilometers
(TDES and AES)encryption.
• WiFi less range and bandwidth WEP and
WPA encryption.also intereference is a
bottleneck.
• WiFi without direct linie of site, but e and d
non line of site.because of multi path
signals,like somehow 802.11n.
WiFi vs. WiMax
• WiMax has spectral limitation, in crowded
areas , the bandwidth may not be
sufficient for a big amount of clients.
• WiFi is free by any AP or Router but
WiMax should be paid huge amounts of
money to have a WiMax in a region.
• Since governments give the license for the
WiMax frequencies.
WiFi vs. WiMax
• New licensed spectrum for WiMAX and
other the valuable 700MHz frequencies
currently used by analog over the air TV.
UWB
• very low energy levels for short-range
high-bandwidth communications by using
a large portion of the radio spectrum.