CWNA

CWNA Review and Chapter Notes 5 – 7

Chapter 5 – IEEE 802.11 Standards

802.11b – HR-DSSS – 2.4 – 2.4835 GHz 1, 2, 5.5 and 11 rates.
802.11a – OFDM – 5GHz UNII Bands – 6, 12, 24 + 9, 18, 36, 48, 54.
802.11g – ERP – 2.4 – 2.45835 GHz – 6, 12, 24 + 9, 18, 36, 48, 54.
– ERP-OFDM – 2.4 – 2.45835 GHz – 6, 12, 24 + 9, 18, 36, 48, 54.
– ERP-DSS/CCK – 1, 2, 5.5, 11 – Backwards Compatible with 802.11b.
802.11d – Country Codes.
802.11h – DFS and TPC and UNII-2 Extended (5.47 – 5.725GHz).
802.11i – CCMP, AES, TKIP, EAP (802.1x), PSK.
802.11j – 
Japan specific ammendment.
802.11e – QoS via HCF and HCCA for time sensitive apps e.g. VoIP.
802.11n – 2.4/5GHz – PHY + MAC enhancements – HT, MIMO.
802.11r-2008 – FT (Fast Transition) for roaming.
802.11k-2008 – RRM.
802.11y-2008 – 3650 – 3700 MHz Band.
802.11w-2009 – Frame Protection for L2 DOS attacks, BIP (Broadcast Integrity Protocol).
802.11z-2010 – Direct Link Setup.
802.11u-2011 – 
External network interoperability (3G/4G).
802.11v-2011 – 
WNM (Wireless Network Management) – Improved Operations.
802.11s-2011
– Mesh Networks.
802.11p – ITS Band (5.9GHz) – High Speed Vehicle Transfer.
802.11aa-2012 – MAC Improvement for AV Streaming.
802.11ac
– VHT, MU-MIMO (5GHz).

Chapter 6 – Wireless Network and Spread Spectrum Technologies

ISM

902 – 928 MHz – (26MHz wide) – Industrial.
2.4 – 2.5 GHz – (100Mhz wide) – Scientific.
5.725 – 5.827 GHz – (150MHz wide) – Medical – Overlaps with UNII-3.

In USA, OFDM (802.11a) is allowed in channel 165 which is rarely used in WLANs therefore it is useful for outdoor bridging.

UNII Bands – Unlicensed National Information Infrastructure Bands

23 Channels in total in 5GHz band.

4 Channels – UNII-1 – Lower – 100 MHz – 5.150 – 5.250 – FCC cap of 50MHz at IR – Indoor use.
4 Channels – UNII-2 – Middle – 100MHz – 5.250 – 5.350 – FCC cap of 250mh at IR. Indoor and Outdoor use.
4 Channels – UNII-3 – Upper – 100MHz – 5.725 – 5.825 – FCC cap of 1000mw – Mostly outdoor.
11 Channels – UNII-2 Extended – 255MHz – 5.470 – 5.725 – FCC cap of 250mw – Indoor / Outdoor – 802.11h.

3.6 GHz

Mostly in US. 3.6 – 3.7 GHz (35 MHz wide).

4.9GHz

Mostly in US for public safety organisations – 4.94 – 4.99GHz (5MHz).
Available in Japan under 802.11lj.

60GHz

802.11ad – VHT (Very High Throughput) – allows up to 7Gbps.

Multipath

Delay spread used to allow multipath signals to arrive simultaneously. Before 802.11n it was detrimental but is now beneficial.

FHSS – Frequency Hopping Spread Spectrum

Originally for v.low speeds.
Once dwell time is reached, hops to another frequency.
79 different frequencies used 2.402 – 2.480GHz.
Normally hops are between 75 – 79 each 1MHz wide.
Defined by Local Authorities.
Typical dwell time is 100 – 200 milliseconds.
Hop time typically low – 200 – 300 microseconds (μs).

Modulation

FHSS – GFSK (Gausian Frequency Shift Keying – No longer tested (clause 14)

DSSS (Direct Sequence Spread Spectrum) – 1 + 2 Mbps (802.11 Clause 15) and 5.5 + 11 Mbps (802.11b clause 18) with HR-DSSS
– Uses Barker Code / CCK (Complementary Code Keying) Methods.
– DBPSK – Differential Binary Phase Shift Keying – 0 and 1
– DQPSK – Differential Quadrature Phase Shift Keying – 00, 01, 10, 11

OFDM

802.11-2007 standard defined use of OFDM.
OFDM – 5GHz – 802.11a.
ERP-OFDM – 2.4GHz – 802.11g.
Not spread spectrum but similar.
Transmits across 52 separate sub-carriers only 312.5KHz in width.
Transmits at lower data rates therefore less chance of ISI.
More resistant to multipath.
Therefore 48 channels/sub-carriers used for data and 4 for phase + amplitude reference info
Convolution Coding or Forward Error Correction (FEC) – 802.11-2007 – used to detect and repair errors
– BPSK and QPSK used for lower rates
– 16 QAM and 64-QAM used for higher rates

Channels

2.4 GHz – 25MHz width
Legacy (DSSS) required 30MHz spacing but no longer used
Sideband / Sidelobe interference can still occur across “non-overlapping” channels so APs should be placed 5-10 feet away from each other

5GHz – 20Mhz width
Outer channels must have their centre 30MHz from the edge of the frequency to stay within limits

Chapter 7 – Wireless Network and Spread Spectrum Technologies

WWAN – Wireless WAN – Fast merging with mobile cellular tech
WMAN – Wireless MAN – WiMAX – 802.11b
WPAN – Wireless Personal Area Network –  Bluetooth, IR, Zigbee
WLAN  – Wireless LAN

Topologies – Components

AP – Thick / Thin
Client Station
Integration Service (IS)  – Conversion of 802.11 frame to 802.3 via AP or WLC
Distribution System (DS)
– Distribution System Medium (DSM) – e.g. 802.3 medium
– Distribution System Services (DSS) – e.g. switch-like AP based software
Wireless Distribution System – Bridges, repeaters, mesh
– Either single band APs for backhaul + clients
– OR dual band APs providing dedicated for each
SSID
– 32 character maximum
– Case Sensitive

BSS (Basic Service Set) – One AP, many clients
BSSID (Basic Service Set ID) – Layer 2 address of radio
ESS – One or more BSS connected via a DSM
IBSS – Just adhoc client stations
Mesh BSS – Mesh discovery + backhaul

Access Point Modes

Bridge
WGB
Repeater
Scanner

Client Station Modes

Infrastructure
Adhoc

Advertisements

One thought on “CWNA Review and Chapter Notes 5 – 7

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s