WirelessWirelessThe Good The BadThe Good The Bad

and the UGLYand the UGLY

Мариян HackMan Маринов<mm@1h.com>

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: 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/

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