IEEE 802.11 Wireless
Local Area Networks

Standardization
St d di ti
Benefits of standardization
Interoperability among the p
p y g products of multiple
p
vendors
Faster product development
Stability
Ability to upgrade
Cost reductions

Interoperability
It bilit

IEEE and 802 committee
d itt
IEEE – Institute of Electrical and Electronic
Engineers
Founded in 1884
Developing standards, publishing technical works,
sponsoring conferences and providing accreditation
conferences,
IEEE 802 LAN/MAN Standards Committee (LMSC)
Develops local area network (LAN) and metropolitan area
network (MAN) standards primarily for the lowest two
layers of the OSI reference model.

802.11 Architecture
802 11 A hit t

IEEE 802.11 Standards
Activities
802.11a:5GHz,
802 11a:5GHz 54Mbps
802.11b:2.4GHz, 11Mbps
802.11g:2.4GHz, 54Mbps

Three Wireless Technologies
802.11a
802.11b 802.11g
Frequency
q y
2.4
2 4 GHz 5 GHz 2.4
2 4 GHz
Band
Worldwide US/AP Worldwide
Availability
Maximum
11 Mbps 54 Mbps 54 Mbps
Data rate
Cordless Phones Cordless Phones
Other
Microwave Ovens HyperLAN Microwave Ovens
Services
Wireless Video Devices Wireless Video
(Interference)
Bluetooth Devices Bluetooth Devices

IEEE 802.11 A hit t
802 11 Architecture

Independent Basic Service Set
(IBSS)
An Independent Basic Service
Set (IBSS) is the simplest
802.11 network type.
It is a network consisting of a
minimum of two stations, where
each station operates with
exactly th same protocol.
tl the t l
No station has priority over
another, the responsibility of
coordinating the medium
access is distributed among all
stations.

Basic Service Set
B i S i S t (BSS)
An infrastructure-based BSS
includes one station that has
access to the wired network
and is therefore referred to
as an Access Point (AP)
(AP).

Extended Service Set (ESS) and
Distributed System (DS)
A BSS may also be part of a
larger network, the so-called
Extended Service Set (ESS).
This ESS consists of one or
more BSS connected over the
BSSs td th
Distribution System (DS).

MAC Layer

802.11
802 11 MAC
Like Ethernet, 802.11 uses CSMA
However,
However instead of collision detection
detection,
collision avoidance is used (CSMA/CA)
The major differences between 802 11
802.11
and Ethernet come from the underline
medium

Challenges f th MAC
Ch ll for the
RF link quality
Noise and multipath fading
Positive acknowledgements are
An atomic operation
required
Hidden node problem
Node 1 and node 3 are “hidden”
Collisions resulting from hidden
nodes are difficult to detect

RTS/CTS clearing
li
To prevent collisions, 802.11 allows stations to
use Request to Send (RTS) and Clear to Send
(CTS) signals to clear out an area

MAC access modes and ti i
d d timing
Access to wireless medium is controlled
by coordination functions
y
Distributed coordination function (DCF)
Ethernet-like CSMA/CA access
Point coordination function (PCF)
Built on DCF
Contention free service

MAC A hit t
Architecture

Career sensing functions and the
network allocation vector
Carrier sensing is used to determine if the
medium is available
Physical career sensing
Difficult and expensive to implement
Virtual career sensing
Provided by NAV
NAV is a timer that indicates the amount of time the medium
will be reserved

Virtual
Vi t l career sensing with NAV
i ith

Interframe Spaces
It f S

MAC S i
Services

MAC S i
Services
Three services are provided by the MAC sublayer in
p y y
IEEE 802.11
Asynchronous data service
This service provides p
p peer LLC entities with the ability to exchange
y g
MAC service data units (MSDUs).
Security services
Security services in IEEE 802.11 are provided by the authentication
service and the Wired Equivalent Privacy (WEP) mechanism
MSDU ordering
The MAC will intentionally reorder MSDUs only if necessary to
improve the likelihood of successful delivery based on the power
management mode of the designated recipient station.

PHY Layer

PHY Functions
F ti
• TheMAC layer is only half the total operation of
802.11. The PHY layer is the other half.
• Physical layer definitions contain 3 functional
entities
•Physical layer convergence procedure (PLCP)
•Maps the MAC frames onto medium
Maps
•Physical medium dependent (PMD) system
•Transmits frames
•Layer management function
y g

802.11 Physical (PHY) Layer
Modulations

IEEE 802.11 PHY protocol
802 11 t l
•On wired LANs a MAC address equates to
LANs,
a location
•In IEEE 802 11 the addressable unit is a
In 802.11,
station (STA). The STA is a message
destination, but it is generally not a fixed
py
physical location

PHY P t
Protocols
l
•They use a medium that has neither absolute nor readily observable
boundaries, outside of which stations will be unable to send or receive
network frames.
•They are unprotected from outside signals.
•They communicate over a medium that is significantly less reliable than
wired media.
•They have dynamic topologies.
•They lack full connectivity. Normally, the assumption is made that every
STA can hear every other STA. This assumption is invalid for WLANs. STAs
may be hidden from each other.
•They have time-varying and asymmetric propagation properties.

IEEE 802.11b (High Rate)
DSSS PHY
802.11b standard is known as the High
Rate PHY for the 2.4 GHz band
This extension builds on the data-rate
capabilities of the original 802 11 standard
802.11
to provide 5.5 and 11 Mbps data rates.
Complementary Code Keying (CCK) is
employed as the modulation scheme.

802.11b
802 11b

2.4
2 4 GHz Channel Sets
Regulatory Domain
Channel Center
Identifier
Id tifi Frequency
F Americas Europe, Middle East and Asia Japan Israel
X
X
X
1 2412 MHz
X
X X
2 2417 MHz
X X
3 X
2422 MHz X
X X X
4 X
2427 MHz
X X
X
5 X
2432 MHz
X
X X
6 X
2437 MHz
MH
7 X X X X
2442 MHz
X
8 X X X
2447 MHz
X X
9 X
2452 MHz X
X
10 X
2457 MHz X
X
11 X
2462 MHz X
X
12 2467 MHz X
X
13 2472 MHz X
2484 MHz
14 X

802.11b (High Rate) operating
channels channels for each geographical area are
The operating
defined as two sets of channels

802.11b Access P i t C
802 11b A Point Coverage
1 Mbps DSSS
p
2 Mbps DSSS
5.5 Mbps DSSS
11 Mbps DSSS

802.11b Scalability
802 11b S l bilit
Total Theoretical Bandwidth = 33 Mbps
Blue
Bl = 11 Mbps
Mb
Green = 11 Mbps
Red = 11 Mbps

Comparing the Technologies
802.11a Data Rates
Data Rate Per
Total Data Rate
Modulation with Subchannel
(Mbps)
Sub Channels (Kbps)
BPSK 125 6
BPSK 187.5 9
QPSK 250 12
QPSK 375 18
16QAM 500 24
16QAM 750 36
64QAM 1000 48
64QAM 1125 54

802.11a
802 11a Channel Sets
Channel Set
Americas i l d
A i include:
ngapore (-S)
mericas (-A)
Taiw (-T)
Argentina Mexico
Jap (-J)
wan
pan
Australia New Zealand Frequency
q y
Am
Sin
Channel ID (MHz)
Austria Panama 34 5170 x
36 5180 x x
Brazil Peru
38 5190 x
Canada Sweden 40 5200 x x
42 5210 x
Chile United 44 5220 x x
Kingdom 46 5230 x
Columbia 48 5240 x x
United States 52 5260 x x
Denmark
56 5280 x x
Venezuela
France 60 5300 x x
64 5320 x x
Cisco Maximum Peak Power (mW)* 40 40 20 40

802.11a Access P i t C
802 11 A Point Coverage
OFDM
54 Mbps
48 Mbps
36 Mbps
24 Mbps
18 Mbps
12 Mb
Mbps
09 Mbps
06 Mbps

802.11a Scalability (Indoor
UNII-1
UNII 1 and 2)
Total Theoretical Bandwidth = 432 Mbps
8 non-overlapping
pp g
channels
54 Mbps
54 Mbps
54 Mbps
54 Mbps
54 Mbps
54 Mbps
54 Mbps
54 Mbps

Client Adapters

Client d t
Cli t adaptors
Radio modules that provide wireless data
communication fixed, portable, or mobile
,p ,
devices and other wireless devices or
wired network infrastructure.
Operate similar to a standard network
product except that the cable is replaced
with a radio connection.

Cisco Aironet 802.11b Client
Adapters
2.4
2 4 GHz
802.11b
11 Mbps
Include
PC C
C Card
PCI Card
LMC Card
Mini PCI

802.11b
802 11b PC C d
Card
2.4 GHz/802.11b
11 Mb
Mbps
Rate Shifting
1, 2, 5.5,
1 2 5 5 and 11Mbps
Fixed data rates
User configurable option
g p
Integrated Antenna
PCMCIA interface
Transmit power settings:
100 mW, 50 mW, 30 mW, 20
mW,
mW 10 mW 5 mW and 1
mW, mW,
mW

802.11b
802 11b LMC C d
Card
2.4 GHz/802.11b
11 Mbps
Rate Shifting
1, 2, 5.5, and 11Mbps
Fixed data rates
User configurable option
U fi bl ti
PCMCIA interface
Transmit power settings:
100 mW, 50 mW, 30 mW, 20
mW, 10 mW, 5 mW, and 1
mW

802.11b
802 11b PCI C d
Card
2.4 GHz/802.11b
11 Mb
Mbps
Rate Shifting
1, 2, 5.5,
1 2 5 5 and 11Mbps
Fixed data rates
User configurable option
g p
RP-TNC Connector
PCMCIA interface
Transmit power settings:
100 mW, 50 mW, 30 mW, 20
mW,
mW 10 mW 5 mW and 1
mW, mW,
mW

802.11b Mini
802 11b Mi i PCI Ad t
Adapter
2.4 GHz/802.11b
2 4 GHz/802 11b
embedded wireless for
notebooks
100 mW transmit
power
Must order through PC
manufactures (not
ft (t
orderable directly
through Ci
th h Cisco))

802.11a CardBus2 Client
Adapter
5 GHz/802.11a
54 Mbps
Rate Shifting
6, 9, 12, 18, 24, 36, 48, or
54
Fixed data rates
User configurable option
5 d Patch Antenna
dBi atc te a
CardBus interface
Transmit power settings:
p g
20 mW, 10 mW, and 5 mW

Parts f
P t of a client adaptor
li t d t
Radio
Half duplex
Antenna
LEDs
Green LED is
G
the Status LED
Orange LED is
g
the RF traffic
LED

LED St t
Status

Windows D i
Wi d Drivers

Linux and M i t h D i
Li d Macintosh Drivers

Downloading Drivers and
Software

Ad-Hoc
Ad H

Infrastructure
If t t