ADVANCED COMPUTER NETWORKS

Unit- IV: Wireless LANS

Introduction, Architectural comparison, Access control, The IEEE 802.11

Project: Architecture, MAC sub layer, Addressing Mechanism, Physical Layer, Bluetooth:
Architecture,

Bluetooth Layers Other Wireless Networks: WIMAX: Services, IEEE project 802.16, Layers in project

802.16, Cellular Telephony: Operations, First Generation (1G), Second Generation (2G), Third
Generation (3G), Fourth Generation (4G), Satellite Networks: Operation, GEO Satellites, MEO
satellites, LEO satellites.

Introduction to Wireless Networks

Wireless networks are communication systems that use electromagnetic waves, such as radio
waves, to transmit data between devices without the need for physical wired connections.
These networks enable mobile communication and are foundational to technologies like Wi-
Fi, Bluetooth, and cellular networks. Wireless communication is essential for providing
access to the internet, connecting devices, and supporting a variety of applications across
different environments.

Wireless networks have become vital for the growth of the Internet of Things (IoT), mobile
applications, and remote communication. These networks can be broadly categorized into
local area networks (LANs), wide area networks (WANs), and personal area networks
(PANs), each serving specific use cases.

Architectural Comparison of Wireless Networks

Wireless networks differ in their architecture, scale, and use cases. Some of the most
common types of wireless networks are:

1. IEEE 802.11 (Wi-Fi): A standard for local area wireless networks (WLANs). It is
widely used to provide internet access in homes, offices, and public spaces. It uses the
2.4 GHz and 5 GHz frequency bands.
2. Bluetooth: Designed for short-range communication, Bluetooth operates within a
small area (typically up to 100 meters) and is used for connecting devices like
smartphones, headsets, and wireless peripherals in personal area networks (PANs).
3. WiMAX: A wireless broadband technology designed for high-speed data
transmission over large areas. It provides internet access for both urban and rural
regions.
4. Cellular Networks: Cellular networks operate over a large geographical area and
provide services like voice calls, text messaging, and mobile data access. Cellular
networks evolve across generations, with each new generation offering improvements
in data speed and capacity.
5. Satellite Networks: Used for long-distance communication, satellite networks
provide global coverage and are used for communication in remote areas, including
weather forecasting, navigation, and internet access.
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Each wireless technology has its specific architecture, such as frequency bands, range, and
protocols, to address different requirements and applications.

Access Control in Wireless Networks

Access control is crucial in wireless networks as multiple devices share the same
communication medium (radio frequency spectrum). Effective access control mechanisms
ensure that devices can communicate without interference or collisions. Common access
control techniques include:

1. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance): Used by

IEEE 802.11 (Wi-Fi) to avoid transmission collisions. Before transmitting data, a
device listens to the medium to check if it’s idle. If the medium is busy, the device
waits until it’s free before sending the data.
2. TDMA (Time Division Multiple Access): Used in cellular networks, this technique
divides the available frequency band into time slots, allowing multiple users to share
the same frequency by transmitting in different time intervals.
3. FDMA (Frequency Division Multiple Access): Divides the frequency spectrum into
multiple channels, with each channel assigned to a user for simultaneous
transmission.

Bluetooth also uses Frequency Hopping for access control, where devices rapidly switch
between different frequency channels to minimize interference and ensure smooth
communication.

The IEEE 802.11 Project (Wi-Fi)

The IEEE 802.11 project defines the standards for wireless local area networks (WLANs).
This family of standards specifies the architecture, protocols, and techniques for wireless
communication, which is commonly known as Wi-Fi.

Architecture of IEEE 802.11

Wi-Fi networks consist of two primary components:

 Access Points (APs): Devices that connect wireless clients to a wired network. They
act as central hubs for communication.
 Stations (STAs): Devices like laptops, smartphones, and tablets that connect to the
network through access points.

The architecture supports a centralized topology where an access point controls and manages
the communication in the network.

MAC Sub-layer
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The MAC (Medium Access Control) sub-layer of the IEEE 802.11 standard manages how
devices access the shared wireless medium. It handles tasks such as:

 Access Control: Ensuring that devices take turns to transmit without colliding.
 Data Fragmentation: Dividing large data into smaller frames for transmission.
 Error Handling: Using mechanisms like checksums and acknowledgment frames to
detect and correct transmission errors.

Addressing Mechanism

IEEE 802.11 uses MAC addresses for addressing. Each device has a unique 48-bit MAC
address that identifies it in the network. There are multiple addresses used in the network:

 BSSID (Basic Service Set Identifier): The unique MAC address of an access point.
 SSID (Service Set Identifier): A logical name used to identify the Wi-Fi network.

Physical Layer

The Physical Layer (PHY) in IEEE 802.11 deals with the actual transmission of data over
the wireless medium. It specifies:

 Radio Frequencies: Wi-Fi typically operates in the 2.4 GHz and 5 GHz frequency
bands.
 Modulation Techniques: Techniques like OFDM (Orthogonal Frequency Division
Multiplexing) and DSSS (Direct Sequence Spread Spectrum) are used for data
encoding and transmission.

Bluetooth

Bluetooth is a wireless technology used for short-range communication between devices,

often within a Personal Area Network (PAN). Bluetooth is widely used for connecting
devices like smartphones, wireless keyboards, and headphones.

Architecture of Bluetooth

Bluetooth consists of several layers:

1. Radio Layer: Defines the transmission medium and radio frequency range.
2. Baseband Layer: Responsible for packet switching and link management, including
device pairing and connection management.
3. Link Manager Protocol (LMP): Manages the creation and maintenance of Bluetooth
links between devices.
4. Logical Link Control and Adaptation Protocol (L2CAP): Handles higher-level
data communication, segmentation, and reassembly of packets.

Bluetooth Layers
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Bluetooth has several layers that manage communication:

 Radio Layer: Deals with signal transmission.

 Baseband Layer: Manages the connection and packet switching.
 LMP (Link Manager Protocol): Responsible for link setup, security, and device
authentication.
 L2CAP (Logical Link Control and Adaptation Protocol): Provides data services to
applications, ensuring proper segmentation and reassembly of data.

Other Wireless Networks

WiMAX (Worldwide Interoperability for Microwave Access)

WiMAX is a wireless broadband technology designed for high-speed internet access over
long distances, from cities to rural areas.

Services

WiMAX provides internet access, voice services, and video streaming across metropolitan
and rural regions.

IEEE 802.16 (WiMAX Standard)

WiMAX is based on the IEEE 802.16 standard, which defines the physical and MAC layers
for broadband wireless communication. WiMAX uses orthogonal frequency-division
multiplexing (OFDM) for efficient data transmission.

Layers in IEEE 802.16

WiMAX’s architecture includes:

 Physical Layer (PHY): Defines the transmission medium and signal modulation.
 MAC Layer: Controls the access to the channel, ensuring efficient data transmission
across the network.

Cellular Telephony

Cellular networks provide wireless mobile communication by dividing large geographical

areas into smaller cells, each served by a base station. As mobile devices move between cells,
calls and data sessions are handed off seamlessly.

Generations of Cellular Networks

 1G (First Generation): The first cellular networks, based on analog technology,

offered voice communication with low capacity and limited range (e.g., AMPS in the
U.S.).
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 2G (Second Generation): Digital networks that provided better call quality, SMS
(text messages), and limited data services (e.g., GSM, CDMA).
 3G (Third Generation): Introduced high-speed internet, video calling, and
multimedia services, providing faster data rates (e.g., UMTS, CDMA2000).
 4G (Fourth Generation): Provided even faster internet speeds, enabling HD video
streaming, online gaming, and high-bandwidth applications, using technologies like
LTE (Long-Term Evolution).

Satellite Networks

Satellite networks use satellites in orbit to provide communication services across the globe.
These networks are especially useful in remote or rural areas where other forms of
communication infrastructure are unavailable.

GEO Satellites (Geostationary Orbit)

GEO satellites orbit at an altitude of about 35,786 km above the Earth's equator. They
provide global coverage and are commonly used for television broadcasting and weather
monitoring. GEO satellites remain fixed over a specific point on Earth.

MEO Satellites (Medium Earth Orbit)

MEO satellites orbit at altitudes between 2,000 and 35,786 km. They provide lower latency
than GEO satellites and are often used for navigation systems, like GPS.

LEO Satellites (Low Earth Orbit)

LEO satellites orbit closer to Earth, at altitudes between 300 and 1,500 km. These satellites
have lower latency and are ideal for real-time communications. Companies like SpaceX's
Starlink use LEO satellites to provide internet access across remote areas.