Lecture 5.7 - Wireless LANs IT & Software Notes | EduRev

IT & Software: Lecture 5.7 - Wireless LANs IT & Software Notes | EduRev

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 Page 1


 
 
 
 
 
 
 
Module 
5 
  
Broadcast Communication 
Networks 
Version 2 CSE IIT, Kharagpur 
 
Page 2


 
 
 
 
 
 
 
Module 
5 
  
Broadcast Communication 
Networks 
Version 2 CSE IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
Lesson
         7
  
 
 
Wireless LANs 
 
Version 2 CSE IIT, Kharagpur 
 
Page 3


 
 
 
 
 
 
 
Module 
5 
  
Broadcast Communication 
Networks 
Version 2 CSE IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
Lesson
         7
  
 
 
Wireless LANs 
 
Version 2 CSE IIT, Kharagpur 
 
Specific Instructional Objectives 
On completion, the student will be able to: 
• Explain the need for wireless LAN  
• Identify the limitations and challenges of  wireless LAN 
• Understand different aspects of IEEE 802.11 WLAN 
o Transmission media                     
o Topology 
o Medium Access Control   
o Security 
 
5.7.1 Introduction 
In the last two decades the wired version of LAN has gained wide popularity and large-
scale deployment. The IEEE 802.3 standard has been revised and extended every few 
years. High-speed versions with transmission rate as high as 1000 Mbps are currently 
available. Until recently wireless version of LANs were not popular because of the 
following reasons: 
• High cost: Previously the equipments cost more. 
• Low data rate: Initially, the data rate supported by the WLAN is too less, so 
it supports only a few applications.  
• Occupational safety concerns  
• Licensing requirements 
In the last couple of years the situation has changed significantly. Cheaper, smaller and 
powerful notebook computers and other mobile computing equipment have proliferated 
in homes and offices. These devices share various resources such as printers, files and 
Broadband Internet connections. This has opened up the need for wireless LAN. Wireless 
LANs also offer a number of other advantages compared to their wired counterpart.  
 
Before going into the technical details of Wireless LAN let us first look at various 
reasons which have led to the development of WLANs. Some of the advantages are 
mentioned below: 
 
• Availability of low-cost portable equipments: Due to the technology 
enhancements, the equipment cost that are required for WLAN set-up have 
reduced a lot.  
• Mobility: An increasing number of LAN users are becoming mobile. These 
mobile users require that they are connected to the network regardless of where 
they are because they want simultaneous access to the network. This makes the 
use of cables, or wired LANs, impractical if not impossible. Wireless LAN can 
provide users mobility, which is likely to increase productivity, user convenience 
and various service opportunities.  
• Installation speed and simplicity: Wireless LANs are very easy to install. There 
is no requirement for wiring every workstation and every room. This ease of 
installation makes wireless LANs inherently flexible. If a workstation must be 
Version 2 CSE IIT, Kharagpur 
 
Page 4


 
 
 
 
 
 
 
Module 
5 
  
Broadcast Communication 
Networks 
Version 2 CSE IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
Lesson
         7
  
 
 
Wireless LANs 
 
Version 2 CSE IIT, Kharagpur 
 
Specific Instructional Objectives 
On completion, the student will be able to: 
• Explain the need for wireless LAN  
• Identify the limitations and challenges of  wireless LAN 
• Understand different aspects of IEEE 802.11 WLAN 
o Transmission media                     
o Topology 
o Medium Access Control   
o Security 
 
5.7.1 Introduction 
In the last two decades the wired version of LAN has gained wide popularity and large-
scale deployment. The IEEE 802.3 standard has been revised and extended every few 
years. High-speed versions with transmission rate as high as 1000 Mbps are currently 
available. Until recently wireless version of LANs were not popular because of the 
following reasons: 
• High cost: Previously the equipments cost more. 
• Low data rate: Initially, the data rate supported by the WLAN is too less, so 
it supports only a few applications.  
• Occupational safety concerns  
• Licensing requirements 
In the last couple of years the situation has changed significantly. Cheaper, smaller and 
powerful notebook computers and other mobile computing equipment have proliferated 
in homes and offices. These devices share various resources such as printers, files and 
Broadband Internet connections. This has opened up the need for wireless LAN. Wireless 
LANs also offer a number of other advantages compared to their wired counterpart.  
 
Before going into the technical details of Wireless LAN let us first look at various 
reasons which have led to the development of WLANs. Some of the advantages are 
mentioned below: 
 
• Availability of low-cost portable equipments: Due to the technology 
enhancements, the equipment cost that are required for WLAN set-up have 
reduced a lot.  
• Mobility: An increasing number of LAN users are becoming mobile. These 
mobile users require that they are connected to the network regardless of where 
they are because they want simultaneous access to the network. This makes the 
use of cables, or wired LANs, impractical if not impossible. Wireless LAN can 
provide users mobility, which is likely to increase productivity, user convenience 
and various service opportunities.  
• Installation speed and simplicity: Wireless LANs are very easy to install. There 
is no requirement for wiring every workstation and every room. This ease of 
installation makes wireless LANs inherently flexible. If a workstation must be 
Version 2 CSE IIT, Kharagpur 
 
moved, it can be done easily and without additional wiring, cable drops or 
reconfiguration of the network. 
• Installation flexibility: If a company moves to a new location, the wireless 
system is much easier to move than ripping up all of the cables that a wired 
system would have snaked throughout the building. This also provides portability. 
Wireless technology allows network to go anywhere wire cannot reach. 
• Reduced cost of ownership: While the initial cost of wireless LAN can be higher 
than the cost of wired LAN hardware, it is envisaged that the overall installation 
expenses and life cycle costs can be significantly lower. Long-term cost-benefits 
are greater in dynamic environment requiring frequent moves and changes.  
• Scalability: Wireless LAN can be configured in a variety of topologies to meet 
the users need and can be easily scaled to cover a large area with thousands of 
users roaming within it. 
 
However, wireless LAN technology needs to overcome a number of inherent 
limitations and challenges. Some of the limitations and challenges are mentioned 
below: 
• Lower reliability due to susceptibility of radio transmission to noise and 
interference. 
• Fluctuation of the strength of the received signal through multiple paths causing 
fading.  
• Vulnerable to eavesdropping leading to security problem. 
• Limited data rate because of the use of spread spectrum transmission techniques 
enforced to ISM band users.  
 
In this lesson we shall introduce the wireless LAN technology based on IEEE 802.11 
standard. Its predecessor the IEEE 802.3, commonly referred to as the Ethernet, is the 
most widely deployed member of the family. IEEE 802.11 is commonly referred to as 
wireless Ethernet because of its close similarity with the IEEE 802.3. Like IEEE 802.3, it 
also defines only two bottom levels of ISO’s open system Interconnection (OSI) model as 
shown in Fig. 5.7.1. As it shares the upper layers with other LAN standards, it is 
relatively easy to bridge the IEEE 802.11 wireless LANs to other IEEE 802.11 wired 
LANs to form an extended interconnected wired and wireless LAN network. Although 
initially wireless LANs were perceived to be as a substitute to wired LANs, now it is 
recognized as an indispensable adjunct to wired LANs. 
 
Version 2 CSE IIT, Kharagpur 
 
Page 5


 
 
 
 
 
 
 
Module 
5 
  
Broadcast Communication 
Networks 
Version 2 CSE IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
Lesson
         7
  
 
 
Wireless LANs 
 
Version 2 CSE IIT, Kharagpur 
 
Specific Instructional Objectives 
On completion, the student will be able to: 
• Explain the need for wireless LAN  
• Identify the limitations and challenges of  wireless LAN 
• Understand different aspects of IEEE 802.11 WLAN 
o Transmission media                     
o Topology 
o Medium Access Control   
o Security 
 
5.7.1 Introduction 
In the last two decades the wired version of LAN has gained wide popularity and large-
scale deployment. The IEEE 802.3 standard has been revised and extended every few 
years. High-speed versions with transmission rate as high as 1000 Mbps are currently 
available. Until recently wireless version of LANs were not popular because of the 
following reasons: 
• High cost: Previously the equipments cost more. 
• Low data rate: Initially, the data rate supported by the WLAN is too less, so 
it supports only a few applications.  
• Occupational safety concerns  
• Licensing requirements 
In the last couple of years the situation has changed significantly. Cheaper, smaller and 
powerful notebook computers and other mobile computing equipment have proliferated 
in homes and offices. These devices share various resources such as printers, files and 
Broadband Internet connections. This has opened up the need for wireless LAN. Wireless 
LANs also offer a number of other advantages compared to their wired counterpart.  
 
Before going into the technical details of Wireless LAN let us first look at various 
reasons which have led to the development of WLANs. Some of the advantages are 
mentioned below: 
 
• Availability of low-cost portable equipments: Due to the technology 
enhancements, the equipment cost that are required for WLAN set-up have 
reduced a lot.  
• Mobility: An increasing number of LAN users are becoming mobile. These 
mobile users require that they are connected to the network regardless of where 
they are because they want simultaneous access to the network. This makes the 
use of cables, or wired LANs, impractical if not impossible. Wireless LAN can 
provide users mobility, which is likely to increase productivity, user convenience 
and various service opportunities.  
• Installation speed and simplicity: Wireless LANs are very easy to install. There 
is no requirement for wiring every workstation and every room. This ease of 
installation makes wireless LANs inherently flexible. If a workstation must be 
Version 2 CSE IIT, Kharagpur 
 
moved, it can be done easily and without additional wiring, cable drops or 
reconfiguration of the network. 
• Installation flexibility: If a company moves to a new location, the wireless 
system is much easier to move than ripping up all of the cables that a wired 
system would have snaked throughout the building. This also provides portability. 
Wireless technology allows network to go anywhere wire cannot reach. 
• Reduced cost of ownership: While the initial cost of wireless LAN can be higher 
than the cost of wired LAN hardware, it is envisaged that the overall installation 
expenses and life cycle costs can be significantly lower. Long-term cost-benefits 
are greater in dynamic environment requiring frequent moves and changes.  
• Scalability: Wireless LAN can be configured in a variety of topologies to meet 
the users need and can be easily scaled to cover a large area with thousands of 
users roaming within it. 
 
However, wireless LAN technology needs to overcome a number of inherent 
limitations and challenges. Some of the limitations and challenges are mentioned 
below: 
• Lower reliability due to susceptibility of radio transmission to noise and 
interference. 
• Fluctuation of the strength of the received signal through multiple paths causing 
fading.  
• Vulnerable to eavesdropping leading to security problem. 
• Limited data rate because of the use of spread spectrum transmission techniques 
enforced to ISM band users.  
 
In this lesson we shall introduce the wireless LAN technology based on IEEE 802.11 
standard. Its predecessor the IEEE 802.3, commonly referred to as the Ethernet, is the 
most widely deployed member of the family. IEEE 802.11 is commonly referred to as 
wireless Ethernet because of its close similarity with the IEEE 802.3. Like IEEE 802.3, it 
also defines only two bottom levels of ISO’s open system Interconnection (OSI) model as 
shown in Fig. 5.7.1. As it shares the upper layers with other LAN standards, it is 
relatively easy to bridge the IEEE 802.11 wireless LANs to other IEEE 802.11 wired 
LANs to form an extended interconnected wired and wireless LAN network. Although 
initially wireless LANs were perceived to be as a substitute to wired LANs, now it is 
recognized as an indispensable adjunct to wired LANs. 
 
Version 2 CSE IIT, Kharagpur 
 
Application Layer 
Presentation Layer 
Session Layer 
Network 
Operating 
System 
(NOS) 
TCP 
IP 
Transport Layer 
Network Layer 
 
 
 OSI         IEEE 802.11 
 
Figure 5.7.1  OSI Reference Model and IEEE 802.11 
 
The IEEE 802.11 standard basically defines the physical and data link layer. In the later 
sections we shall look at detailed implementations. 
 
5.7.2 Transmission Media 
There are three media that can be used for transmission over wireless LANs. Infrared, 
radio frequency and microwave. In 1985 the United States released the industrial, 
scientific, and medical (ISM) frequency bands. These bands are 902 - 928MHz, 2.4 - 
2.4853 GHz, and 5.725 - 5.85 GHz and do not require licensing by the Federal 
Communications Commission (FCC). This prompted most of the wireless LAN products 
to operate within ISM bands. The FCC did put restrictions on the ISM bands however. In 
the U.S. radio frequency (RF) systems must implement spread spectrum technology. RF 
systems must confine the emitted spectrum to a band. RF is also limited to one watt of 
power. Microwave systems are considered very low power systems and must operate at 
500 milliwatts or less.  
 
5.7.2.1 Infrared 
Infrared systems (IR systems) are simple in design and therefore inexpensive. They use 
the same signal frequencies used on fiber optic links. IR systems detect only the 
amplitude of the signal and so interference is greatly reduced. These systems are not 
bandwidth limited and thus can achieve transmission speeds greater than the other 
systems. Infrared transmission operates in the light spectrum and does not require a 
license from the FCC to operate. There are two conventional ways to set up an IR LAN.  
Logical Link Layer (LLC) 802.2 
Data Link Layer 
802.11b 
Medium Access Control (MAC) 
Physical Layer 
Version 2 CSE IIT, Kharagpur 
 
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