4. Introduction
# Wireless Technology is an
alternative to Wired
Technology, which is commonly
used, for connecting devices in
wireless mode.
# Wi-Fi (Wireless Fidelity) is a generic
term that refers to the IEEE 802.11
communications standard for
Wireless Local Area Networks 4
5. The Wi-Fi Technology
Wi-Fi Networks use Radio
Technologies to transmit &
receive data at high speed:
# IEEE 802.11b(1999)
# IEEE 802.11a(2001)
# IEEE 802.11g(2003) 5
6. 802.11 Physical Layer
# There are three sub layers in
physical layer: 1. Direct
Sequence Spread Spectrum
(DSSS)
2.Frequency Hoping Spread
Spectrum (FHSS)
3.Diffused Infrared (DFIR) - Wide
angle 6
7. DSSS
# Direct sequence signaling technique
divides the 2.4 GHz band into 11 22-
MHz channels. Adjacent channels
overlap one another partially, with
three of the 11 being completely non-
overlapping. Data is sent across one
of these 22 MHz channels without
hopping to other channels.
7
8. IEEE 802.11 Data Link
Layer
The data link layer consists of two
sub-layers :
* Logical Link Control (LLC)
* Media Access Control
(MAC).
802.11 uses the same 802.2 LLC
and 48-bit addressing as other 802
LANs, allowing for very simple
8
bridging from wireless to IEEE
9. 802.11 Media Access Control
# Carrier Sense Medium Access with collision avoidance
protocol (CSMA/CA)
** Listen before talking
** Avoid collision by explicit Acknowledgement (ACK)
** Problem: additional overhead of ACK packets, so slow
performance
# Request to Send/Clear to Send (RTS/CTS)
protocol
• Solution for “hidden node” problem
• Problem: Adds additional overhead by
temporarily reserving the medium, so used for
large size packets only retransmission would be
expensive
# Power Management
9
10. Elements of a WI-FI Network
# Access Point (AP) - The AP is a
wireless LAN transceiver or “base station” that
can connect one or many wireless devices
simultaneously to the Internet.
# Wi-Fi cards - They accept the wireless
signal and relay information.They can be
internal and external.(e.g PCMCIA Card for
Laptop and PCI Card for Desktop PC)
10
# Safeguards - Firewalls and anti-virus
11. How a Wi-Fi Network Works
# Basic concept is same as Walkie talkies.
# A Wi-Fi hotspot is created by installing an
access point to an internet connection.
# An access point acts as a base station.
# When Wi-Fi enabled device encounters a
hotspot the device can then connect to that
network wirelessly.
# A single access point can support up to 30
users and can function within a range of 100 –
150 feet indoors and up to 300 feet outdoors.
# Many access points can be connected to each
11
13. AP-based topology
# The client communicate through Access
Point.
# BSA-RF coverage provided by an AP.
# ESA-It consists of 2 or more BSA.
# ESA cell includes 10-15% overlap to
allow roaming.
13
14. Peer-to-peer topology
# AP is not required.
# Client devices within a
cell can communicate
directly with each
other.
# It is useful for setting
up of a wireless
network quickly and
easily.
14
15. Point-to-multipoint bridge topology
This is used to connect a LAN in one building to
a LANs in other buildings even if the buildings
are miles apart . These conditions receive a
clear line of sight between buildings. The line-of-
sight range varies based on the type of wireless
bridge and antenna used as well as the
environmental conditions.
15
19. Service Set Identifier (SSID)
• SSID is used to identify an
802.11 network
• It can be pre-configured or
advertised in beacon
broadcast
• It is transmitted in clear text
• Provide very little security 19
20. Wired Equivalent Privacy
Or i g i n a l
(WEP) t y s o l u t i
s e c u r i o n
o f f e r e d b y t h e I EEE 802.11
s t a n d a r d
Us e s RC4 e n c r y p t i o n wi t h
p r e -s h a r e d k e y s a n d 24 b i t
i n i t i a l i z a t i o n v e c t o r s (I V )
k e y s c h e d u l e i s g e n e r a t e d
b y c o n c a t e n a t i n g t h e s h a r e d
s e c r e t k e y wi t h a r a n d o m
g e n e r a t e d 24-b i t I V
32 b i t I C V (I n t e g r i t y c h e c k
v a l u e )
No . o f b i t s i n k e y s c h e d u l e i s
e q u a l t o s u m o f l e n g t h o 20
f
t h e p l a i n t e x t a n d I CV
21. 802.1x Access
• Designed as aControl network access
general purpose
control mechanism
• Authenticate each client connected to AP (for
WLAN) or switch port (for Ethernet)
• Authentication is done with the RADIUS
server, which ”tells” the access point whether
access to controlled ports should be allowed
or not
• AP forces the user into an unauthorized state
• user send an EAP start message
• AP return an EAP message requesting the user’s
identity
• Identity send by user is then forwared to the
authentication server by AP 21
22. Wireless Protected Access
(WPA)
# WPA is a specification of standard based, interoperable
security enhancements that strongly increase the level of data
protection and access control for existing and future wireless
LAN system.
• User Authentication
• 802.1x
• EAP
# TKIP (Temporal Key Integrity Protocol) encryption
• RC4, dynamic encryption keys (session based)
• 48 bit IV
• per packet key mixing function
• Fixes all issues found from WEP
• Uses Message Integrity Code (MIC) Michael
• Ensures data integrity
• Old hardware should be upgradeable to WPA
# WPA comes in two flavors
WPA-PSK
22
•
23. Wi-Fi technology is the non-
cable connection between the
# Limitation:
access point or router and • Degradation in
the PC. The PC remotely
connects to the internet performance
without any wires or cables. • High power
In some cases, Wi-Fi tech.
requires you to have the WEP • consumption
or WPA key to access.
WEP/WPA is like the • Interference
password to secure your • Limited range
wireless router/ access
point.
# Advantages:
• Mobility, Ease of Installation
• Flexibility, Cost
• Reliability,Security 23
