This document discusses wireless networking and WiFi protocols. It provides an overview of radio frequency, WiFi standards like 802.11g, different types of radio antennas, factors that impact WiFi signals, and WiFi protocols such as 802.11a/b/g/n/ac. It also covers OpenWRT configuration options for wireless settings including bitrate, transmit power, beacon settings, and channel bandwidth.

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