INTRODUCTION
To Wireless Networks
Wireless Comes of Age
• Guglielmo Marconi invented the wireless telegraph in
1896
– Communication by encoding alphanumeric characters in
analog signal
– Sent telegraphic signals across the Atlantic Ocean
• Communications satellites launched in 1960s
• Advances in wireless technology
– Radio, television, mobile telephone, communication
satellites
• More recently
– Broadband wireless networking, cellular technology
Broadband Wireless Technology
• Higher data rates obtainable with broadband wireless
technology
– Graphics, video, audio
• Shares same advantages of all wireless services:
convenience and reduced cost
– Service can be deployed faster than fixed service
– No cost of cable plant
– Service is mobile, deployed almost anywhere
Limitations and Difficulties of
Wireless Technologies
• Wireless is convenient and less expensive
• Limitations and political and technical difficulties
inhibit wireless technologies
• Lack of an industry-wide standard
• Device limitations
– E.g., small LCD on a mobile telephone can only displaying
a few lines of text
– E.g., browsers of most mobile wireless devices use wireless
markup language (WML) instead of HTML
A Wireless Network
Definition:
A Group of interconnected nodes that exchange
information and share resources through a
wireless transmission medium
TYPES OF WIRELESS
NETWORKS
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Wireless PAN
Wireless LAN
Wireless Broadband
Wireless WAN (satellite , Microwave ,..etc)
Cellular Networks
Characteristics of Wireless WANs
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Covers large geographical areas
Circuits provided by a common carrier
Consists of interconnected switching nodes
Traditional WANs provide modest capacity
– 64000 bps common
– Business subscribers using T-1 service – 1.544 Mbps
common
• Higher-speed Wireless WANs use satellite , and 10s
of Mbps common
Characteristics of Wireless LANs
• Like WAN, Wireless LAN interconnects a
variety of devices and provides a means for
information exchange among them
• Traditional Wireless LANs
– Provide data rates of 1 to 20 Mbps
• High-speed Wireless LANS
– Provide data rates of 100 Mbps
• Standards for Wireless LANS is WI-FI
Characteristics of Wireless LANs
• Used to be a network with high prices, low data
rates, occupational safety concerns, and licensing
requirements
• Problems have been addressed and popularity of
wireless LANs has grown rapidly
Differences between Wireless
LANs and WANs
• Scope of a LAN is smaller
– LAN interconnects devices within a single
building or cluster of buildings
• LAN usually owned by organization that owns
the attached devices
– For WANs, most of network assets are not owned
by same organization
• Internal data rate of LAN is much greater
The Need for Wireless MANs
• Traditional point-to-point and switched network
techniques used in WANs are inadequate for growing
needs of organizations
• Need for high capacity and low costs over large area
• MAN provides:
– Service to customers in metropolitan areas
– Required capacity
– Lower cost and greater efficiency than equivalent service
from telephone company
• Standards for Wireless MANS is WI-MAX
Wireless Standards
• PAN , LAN and MAN standards were defined by
IEEE and Industrial forums
• A LAN standard define media, coding scheme, frame
form at , MAC protocol and other data link layer
protocols :
• Examples of standards :
– Wireless PAN: Bluetooth , IEEE 802.15
– Wireless LAN : IEEE 802.11 (a ,b , g )
– Broadband Wireless Networks : IEEE 803.16
Wireless LAN Configurations
• A wireless LAN uses wireless transmission
medium in a local Area in :
– Single Cell Configuration - Multi-cell Configuration
– Infrastructure Wireless LAN
– - Add Hoc LAN
Single Cell Wireless LAN
Configuration
Multi-Cell Wireless LAN
Configuration
Infrastructure Wireless LAN
Add Hoc LAN
Factors To Consider:
For Wireless LAN
• Same as any LAN
– High capacity, short distances, full connectivity, broadcast capability
• Throughput: efficient use wireless medium
• Number of nodes:Hundreds of nodes across multiple cells
• Connection to backbone LAN: Use control modules to connect
to both types of LANs
• Service area: 100 to 300 m
• Low power consumption:Need long battery life on mobile
stations
– Mustn't require nodes to monitor access points or frequent handshakes
• Transmission robustness and security:Interference prone and
easily eavesdropped
Factors To Consider:
For Wireless LAN
• Collocated network operation:Two or more
wireless LANs in same area
• License-free operation
• Handoff/roaming: Move from one cell to
another
• Dynamic configuration: Addition, deletion, and
relocation of end systems without disruption to
users
Wireless LAN Applications
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LAN Extension
Cross-Building Interconnect
Nomadic Access
Ad Hoc Networking
Applications - LAN Extension
• Saves installation of LAN cabling
• Eases relocation and other modifications to network
structure
• Wireless LAN to replace wired LANs has not
happened
• In some environments, role for the wireless LAN
– Buildings with large open areas
• Manufacturing plants, stock exchange trading floors, warehouses
• Historical buildings
• Small offices where wired LANs not economical
• May also have wired LAN
– Servers and stationary workstations
Applications –
Cross-Building Interconnect
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Connect LANs in nearby buildings
Point-to-point wireless link
Connect bridges or routers
Not a LAN per se
– Usual to include this application under heading of
wireless LAN
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Applications - Nomadic Access
• Link between LAN hub and mobile data
terminal
– Laptop or notepad computer
– Enable employee returning from trip to transfer data
from portable computer to server
• Also useful in extended environment such as
campus or cluster of buildings
– Users move around with portable computers
– May wish access to servers on wired LAN
Applications –
Ad Hoc Networking
• Peer-to-peer network
• Set up temporarily to meet some immediate
need
• E.g. group of employees, each with laptop or
palmtop, in business or classroom meeting
• Network for duration of meeting