WiFi basics and practical considerations

1. WirelessWireless
The Good The BadThe Good The Bad
and the UGLYand the UGLY
Мариян HackMan Маринов
<mm@1h.com>

2. 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

3. What you will hear :)What you will hear :)
➢Radio frequency
➢Radio antennas
➢WiFi protocols
➢WiFi protocol options
➢OpenWRT configuration options

4. 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

5. FrequencyFrequency
➢It does not exist... :)

6. Radio waveRadio wave

7. FrequencyFrequency

8. FrequenciesFrequencies
➢Human hearing: 20Hz to 20KHz
➢Radio: 3 kHz to 300 GHz
➢More info here:
http://ironbark.xtelco.com.au/subjects/DC/lectures/7/

9. ModulationsModulations

12. 802.11g802.11g
➢Припокриващи се канали
➢Други технологии на същите честоти
2.412Ghz – 2.472Ghz
5.170Ghz – 5.320Ghz
5.500Ghz – 5.700Ghz

13. Radio antennasRadio antennas
➢Different types based on direction
➢ Omni-directional
➢ Directional
➢Based on design
➢ A LOT :)
➢ Dipol
➢ Loop
➢ Blade
➢ Slot
➢ YAGI

14. Radio antennasRadio antennas

15. Dipol antenna radiation

17. Blade antenna

19. Slot antennaSlot antenna

20. Slot antennaSlot antenna

21. WiFi signal impactWiFi signal impact
➢Reflection
➢Refraction - different speed
➢Diffraction - go around objects
➢Scattering - dust, humidity
➢Absorption

22. 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

23. Signal dispersionSignal dispersion

24. 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/

25. 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

26. Assemble frame
Is the
channel
free
Wait for Random
backoff time
Transmit RTS
CTS
Received
Transmit application
Data
RTS - Ready to Send
CTS – Clear to Send
CSMA/CA

27. Въпроси?Въпроси?
Мариян HackMan MarinovМариян HackMan Marinov
E-Mail:E-Mail: mm@1h.commm@1h.com
IRC: irc.freenode.net HackManIRC: irc.freenode.net HackMan
ICQ: 7556201ICQ: 7556201
Jabber/Gtalk:Jabber/Gtalk: hackman@jabber.orghackman@jabber.org
http://github.com/hackman/http://github.com/hackman/

28. 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

29. OpenWRTOpenWRT