Wifi the good bad and ugly
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Wireless Wireless The Good The Bad The Good The Bad and the UGLY and the UGLY Мариян HackMan Маринов <[email protected]>
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Transcript of Wifi the good bad and ugly
WirelessWirelessThe Good The BadThe Good The Bad
and the UGLYand the UGLY
Мариян HackMan Маринов<[email protected]>
Who am I?Who am I?
➢ Chief system architect of
➢ Sysadmin since the stone age
➢ Linux Sysadmin & Network security
courses in FMI Sofia and SoftUni
What you will hear :)What you will hear :)
➢Radio frequency
➢Radio antennas
➢WiFi protocols
➢WiFi protocol options
➢OpenWRT configuration options
No Brands HereNo Brands Here
➢Everything I will be showing should be considered brand neutral
➢I have strong affinity toward atheros WiFi chips, but that is all
FrequencyFrequency
➢It does not exist... :)
Radio waveRadio wave
FrequencyFrequency
FrequenciesFrequencies
➢Human hearing: 20Hz to 20KHz
➢Radio: 3 kHz to 300 GHz
➢More info here:
http://ironbark.xtelco.com.au/subjects/DC/lectures/7/
ModulationsModulations
802.11g802.11g
➢Припокриващи се канали
➢Други технологии на същите честоти2.412Ghz – 2.472Ghz5.170Ghz – 5.320Ghz5.500Ghz – 5.700Ghz
Radio antennasRadio antennas
➢Different types based on direction➢ Omni-directional
➢ Directional
➢Based on design➢ A LOT :)
➢ Dipol
➢ Loop
➢ Blade
➢ Slot
➢ YAGI
Radio antennasRadio antennas
Dipol antenna radiation
Blade antenna
Slot antennaSlot antenna
Slot antennaSlot antenna
WiFi signal impactWiFi signal impact
➢Reflection
➢Refraction - different speed
➢Diffraction - go around objects
➢Scattering - dust, humidity
➢Absorption
WiFi signal absorptionWiFi signal absorption
➢Plasterboard/drywall 3-5 dB
➢Glass wall and metal frame 6 dB
➢Metal door 6-10 dB
➢Window 3 dB
➢Concrete wall 6-15 dB
➢Block wall 4-6 dB
Signal dispersionSignal dispersion
WiFi protocolsWiFi protocols
➢IEEE➢Standards
➢http://standards.ieee.org/getieee802/802.11.html
➢Wi-Fi Alliance➢Certification, Interop and Early Standards
➢http://www.wi-fi.org/
WiFi protocolsWiFi protocols➢ 802.11-2007, 802.11-2011, 802.11-2012
➢ 802.11 a,b,g,n,ac➢ 802.11i – WPA2
➢ 802.11w – Protected management frames
➢Drafts➢ Draft 802.11s – Mesh networking
➢ Draft 802.11u – Interworking with external networks
WPA – replaced by WPA2 WPS
HALF DUPLEX COMMUNICATIONHALF DUPLEX COMMUNICATION
Assemble frame
Is the channel
free
Wait for Random backoff time
Transmit RTS
CTSReceived
Transmit applicationData
RTS - Ready to SendCTS – Clear to Send
CSMA/CA
Въпроси?Въпроси?
Мариян HackMan MarinovМариян HackMan Marinov
E-Mail: E-Mail: [email protected]@1h.com
IRC: irc.freenode.net HackManIRC: irc.freenode.net HackMan
ICQ: 7556201ICQ: 7556201
Jabber/Gtalk: Jabber/Gtalk: [email protected]@jabber.org
http://github.com/hackman/http://github.com/hackman/
WiFi protocol optionsWiFi protocol options
➢Bitrate
➢TX Power
➢beacon
➢mcast_rate
➢Channel bonding (HT20, HT40, HT80, HT160)
➢Channel bandwidth 5, 10, 20
➢antenna - horizontal/vertical
➢country
http://wiki.openwrt.org/doc/uci/wireless
OpenWRTOpenWRT
