WLANs

wireless access point (AP) instead of an Ethernet switch.

• 802.11 prescribes collision-avoidance instead of collision-

detection

each client uses a wireless adapter to gain through a wireless router or

access point.

What required to access Wlan?

• 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

• 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.

WiFi vs. WiMax

UWB

• very low energy levels for short-range high-bandwidth communications by using a large portion of the radio spectrum.