Wireless Basics

NA wireless candidate you are expected toETSI (Europe) = 13 Channels, each channel is
understand how RF signals are employed to send22Mhz wide
data over the airwave.Japan = 14 Channels, each channel is 22Mhz wide
Basics of CCNA Wireless.Many of the channels overlap and it is advised to
The IEEE worked on a created a specificationuse non-overlapping channels, the 3
which defines how to use the same frequency innon-overlapping channels are 1, 6 and 11.
half duplex to send and receive over a wireless5Ghz
LAN. The Specification is known as 802.11.Used by 802.11a and 802.11n.
To use the frequencies specified by the IEEEFor 802.11a the data rates range from 6Mbps to
802.11 standards do not require any licensing on54Mbps
the part of the user provided the user adheres toThe 802.11 Specifications
the rules laid down by the IEEE.802.11b Specification
Each country or region has a regulatory bodyFrequency Spectrum = 2.4Ghz
(FCC in North America and ETSI in Europe) whichRF technology used = DSSS (Direct Sequence
regulates the frequencies that can be used alongSpread Spectrum)
with the amount of power which the WirelessNon-Overlapping Channels = 1, 6 and 11
device can operate at and the types ofModulation = DQPSK and DBPSK
transmission technologies which may be employed.Data Rates = 1 , 2 , 5,5 and 11Mbps
(ETSI is an official non-profit organisation. ETSI isCoding = Barker 11 and CCK (Complementary
responsible for standardises power levels andCode Keying)
frequencies in Europe)802.11b is an improvement on simple 802.11 which
In 1986 the in North America the FCC allowed thecould only achieve data rates of 1 or 2Mbps.
use of a technology called “Spread802.11b was designed to be backwards compatible
Spectrum” within the commercial market in awith 802.11 using Barker 11 coding when it is
frequency band referred to as the Industry,required and CCK when not required to be
Scientific and Medical (ISM) frequency bands.compatible with 802.11.
Bandwidth and Datarate802.11b also allows for clients to dynamically shift
In the data world we are used to using the termtheir data rates as they move away from the
“bandwidth” to refer to the amount of dataaccess point and gain speed as they move closer
passing a fixed point per second measured in bits,to the access point.
kilobits, megabits and gigabits. These use of the802.11g Specification
term bandwidth is not technically correct. TheFrequency Spectrum = 2.4Ghz
correct term would be “datarate”.RF technology used = OFDM (Orthogonal
When we speak of bandwidth we refer to thefrequency Division Multiplexing) and DSSS
number of cycles per second. One cycle is onNon-Overlapping Channels = 1, 6 and 11
Hertz. A hertz is measures how many cycles perModulation = DQPSK and DBPSK
second. Some examples are FM radio would useData Rates = 1, 2, 5,5 and 11Mbps with DSSS and
175Khz and Television is around 4500Khz.6, 9, 12, 18, 24, 36, 48, 54Mbps with OFDM
Electromagnetic SpectrumCoding = Barker 11 and CCK (Complementary
Extremely low Frequency (ELF) 3Hz to 30HzCode Keying)
Super Low Frequency (SLF) 30Hz to 300HzThe 802.11g specification allows for an additional 8
Ultra Low Frequency (ULF) 300Hz to 3Khzmore data rates up to 54Mbps just like 802.11a.
Very Low Frequency (VLF) 3Khz to 30Khz802.11g is also compatible with 802.11b by using
Low Frequency (LF) 30Khz to 300Khzidentical coding and modulation, but 802.11g will
Medium Frequency (MF) 300Khz to 3Mhzonly drop back to 802.11b rates when it is
High Frequency (HF) 3Mhz to 30Mhznegotiating access to the medium after which it
Very High Frequency (VHF) 30Mhz to 300Mhzwill transmit at 802.11g rates
Ultra High Frequency (UHF) 300Mhz to 3GhzYou must always bear in mind that it still uses the
Super High Frequency (SHF) 3Ghz to 30Ghz2.4Ghz frequency and as such will only have 3
Extremely High Frequency (EHF) 30Ghz tonon-overlapping channels, 1, 6 and 11.
300Ghz802.11a Specification
Which frequencies can be used depends on theFrequency Spectrum = 5Ghz
country that you happen to be in. Europe allowsRF technology used = OFDM (Orthogonal
the use of the 2.4Ghz and 5Ghz ranges, thesefrequency Division Multiplexing) and DSSS
ranges are known as the CIPT A, B, C bands.Non-Overlapping Channels = 4 non-overlapping
2.4Ghzchannels per band, middle 8 channels are used wih
CEPT A = 5.15-5.25Ghz52 sub-carriers on each channel
CEPT B = 5.25-5.35GhzModulation = DQPSK and DBPSK
CEPT C = 5.47-5.725GhzData Rates = 1, 2, 5,5 and 11Mbps with DSSS and
North America uses Unlicensed National6, 9, 12, 18, 24, 36, 48, 54Mbps with OFDM
Informational Infrastructure (UNII) bands.UNII-1 is designed for use indoor, UNII is designed
900Mhzfor use outdoor with an external antenna and
2.4Ghz ISMUNII-3 is designed for use for outdoor bridges and
UNII-1 = 5.15-5.25Ghzexternal antennas.
UNII-2 = 5.25-5.35Ghz4 non-overlapping channels per band (Each band is
UNII-2 Extended = 5.47-5.725Ghzeither UNII-1 = low, UNII-2=Middle, UNII-3=High).
900MhzConsumers normally use the middle and low
Range: 900Mhz — Start 902Mhz through tobands. With 4 non over lapping channels per band.
928MhzEach channel in each band in turn has 52
Used for Coreless Phonessub-carriers on each channel Low and middle
2.4Ghzchannels are broken into a total of eight channels
Used by 802.11, 802.11b, 802.11g, 802.11g andof 20Mhz each, each of these 20Mhz channels are
802.11nthen divided into 52 sub-carriers of 300khz each.
The 2.4Ghz Channel is divided into sub-channels.ETSI permits the use of 19 channels along with
The number of usable sub-channels depends onsupporting dynamic Frequency Control to avoid
the country:interfering with Radar which also occupies the
North America = 11 Channels, each channel issame frequency band.
22Mhz wide802.