Communication and Networks Assignment
Communications and Networks
version 1.0
Diploma in Information Technology
Copyright © 2020 by Singapore Institute of Management Pte Ltd. All rights reserved.
Lesson 18: Wireless Networking
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Lesson 18 Learning Outcomes
Describe the different PAN technologies and standards
Explain the wireless LAN architecture
Explain how contention is resolved in a wireless LAN
Describe wireless WAN technologies
Explain the concept of cell clusters
Understand the different generations of cellular technologies
Describe the role of GPS and VSAT satellites
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Lesson 18 Outline
PAN Technologies
LAN & MAN Technologies
WAN Technologies
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Wireless Networks Types
Government regulations make specific ranges of the electromagnetic spectrum available for communication
License is required to operate transmission equipment in some parts of the spectrum
Some parts of the spectrum are unlicensed
Source: Douglas, C (2016) Computer Networks and Internets
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Personal Area Networks (PANs)
PAN provides communication over a short distance intended for devices owned and operated by a single user
Example: wireless headset and cell phone
Source: Douglas, C (2016) Computer Networks and Internets
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Bluetooth Illustration
Source: Douglas, C (2016) Computer Networks and Internets
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Ultra Wideband (UWB)
UWB consumes low power to reach same distance
Idea behind is spreading data across many frequencies
Uses wide spectrum of frequencies
Short distance: 2m-10m
Signal permeates obstacles such as walls
Data rate of 110 at 10 meters, and up to 500 Mbps at 2 meters
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Zigbee
Zigbee: arose from desire to standardise wireless remote-control technology especially for industrial equipment
Only send short command, high data rates are not required
Wireless standard for remote control, not data
Frequency bands, 868 MHz 915 MHz, 2.4 GHz
Data rate of 20-250 Kbps, depending on frequency band
Low power consumption
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Zigbee Applications
Source: Douglas, C (2016) Computer Networks and Internets
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InfraRED
InfraRED: often used in remote controls
Range of 1 to several meters
Directional transmission with a cone covering 30o
Data rates 2.4Kbps (control) to 16Mbps (data)
Generally low power consumption
Signal may reflect from surfaces but cannot penetrate solid objects
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RFID
Radio Frequency Identification (RFID)
A small tag contains identification information that a receiver can “pull” from the tag
Passive tags: draw power from the signal sent by the reader
Active tags: contain a battery which may last up to 10 years
Can use frequencies < 100MHz to 868-954 MHz
Used for inventory control, sensors, passports, and other applications
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RFID Applications
Source: Douglas, C (2016) Computer Networks and Internets
RFID tag
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ISM Wireless Bands
ISM Wireless is a region of electromagnetic spectrum reserved for use by Industrial, Scientific, and Medical purposes
Not licensed to specific carriers and are used for LAN/PAN
Source: Douglas, C (2016) Computer Networks and Internets
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Practice 18.1
Suggest appropriate PAN technology for the following criteria:
Multiple devices, line of sight not required, public use
Smart home purposes, line of sight not required
Industrial, scientific and medical purposes
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Lesson 18 Outline
PAN Technologies
LAN & MAN Technologies
Wi-Fi Technology
WiMax Technology
WAN Technologies
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Wireless LAN Technologies
IEEE provides most wireless LAN standards (IEEE 802.11)
Group of vendors who build wireless equipment formed Wi-Fi Alliance to test and certify equipment meant for 802.11 standards
Thus, most consumers associate wireless LANs with Wi-Fi
Source: Douglas, C (2016) Computer Networks and Internets
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Spread Spectrum
Spread spectrum: multiple frequencies to send data
sender spreads data across multiple frequencies
receiver combines information from multiple frequencies to reproduce original
Can be used to achieve one of the following:
Increase overall performance
Make transmission more immune to noise
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Spread Spectrum Techniques
When a wireless technology is defined, designers choose appropriate multiplexing technique
Source: Douglas, C (2016) Computer Networks and Internets
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Wireless LAN (WLAN) Architecture
Building blocks of WLAN:
Access Points (AP): also called base stations
Interconnection mechanism: like switch or router used to connect APs
Set of wireless hosts/nodes
Two possible WLAN configurations:
Ad hoc: wireless hosts communicate amongst themselves without a base station
Infrastructure based: wireless host only communicates with AP that relays all packets
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WLAN Illustration
Source: Douglas, C (2016) Computer Networks and Internets
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Overlaps & Dead Zone
Dead zone: physical location with no wireless connectivity
Overlap: wireless host can reach multiple APs
To handle this, host can associate with an AP
Source: Douglas, C (2016) Computer Networks and Internets
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AP Coordination
APs communicated amongst themselves to ensure smooth handoff
AP also allows measuring signal strength and move a host to AP that have stronger signal
Some vendors offers lower cost, less complex APs that do not coordinate
Argued that signal strength does not provide a valid measure of mobility
Mobile computer can handle changing from one AP to another
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Handling Contention in WLAN
Wi-Fi employs collision avoidance methods.
CSMA/CA triggers a brief transmission from the intended receiver before transmitting a packet
Source: Douglas, C (2016) Computer Networks and Internets
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Lesson 18 Outline
PAN Technologies
LAN & MAN Technologies
Wi-Fi Technology
WiMax Technology
WAN Technologies
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WiMax
WiMax: World-wide Interoperability for Microwave Access
WiMAX Forum promote use of the technology
Can be used as an Internet access technology
Two main versions of WiMAX,
Fixed WiMAX: does not provide for handoff among access points
Mobile WiMAX: technology offers handoff among APs
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WiMax Deployment
Can be used as backhaul connection between ISP facility and remote locations like cell towers
Use frequencies with clear Line-Of-Sight (LOS)
Internet access can use frequencies with Non-Line-Of-Sight (NLOS) deployment
Source: Douglas, C (2016) Computer Networks and Internets
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WiMax Key Features
Uses licensed spectrum (i.e., offered by carriers)
Each cell can cover a radius of 3 to 10 Km
Uses scalable orthogonal FDM
Guarantees quality of services (for voice or video)
Can transport 70 Mbps in each direction at short distances
Provides 10 Mbps over a long distance (10 Km)
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Lesson 18 Outline
PAN Technologies
LAN & MAN Technologies
WAN Technologies
Cellular Technologies
Satellite Technologies
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How Do Satellites Stay in Orbit
Source: https://www.youtube.com/watch?v=IC1JQu9xGHQ
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Cellular Communication Systems
Cellular communication system: provides voice and data services and Internet Connectivity
Each cell contains a tower and group of cells are connected to a Mobile Switching Center (MSC)
MSC tracks mobile users and manages handoff as the user passes from one cell to another
Source: Douglas, C (2016) Computer Networks and Internets
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Handoff Approaches
Handoff can occur:
Same MSC if moving within same group of cells
Another MSC if moving to another group of cells
Perfect coverage occurs if each cell is a hexagon
But in practice, coverage is imperfect
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Cell Tower Signals
Most cell towers use omnidirectional antennas that transmit in a circular pattern
Cells overlap and gaps exist with no coverage
Theoretical
In practice
Source: Douglas, C (2016) Computer Networks and Internets
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Cell Density
Variability of cell density is possible
Rural areas: each cell is large, a single tower is adequate for a large area
Urban areas: various size cells with smaller cells covering metropolitan areas
Designers break a region into many cells to handle more calls
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Cell Clusters
Interference can be minimized if adjacent cells do not use the same frequency
Cellular planners employ a cluster approach in which a small pattern of cells is replicated
Source: Douglas, C (2016) Computer Networks and Internets
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Cell Clusters Approach
For a cell assigned to a unique frequency, the repeated pattern will not be assigned to any adjacent cells
Source: Douglas, C (2016) Computer Networks and Internets
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Cellular Technologies
Four generations: 1G, 2G, 3G, and 4G with intermediate versions like 2.5G and 3.5G
1G (1970s-1980s): analog signals to carry voice
2G & 2.5G (1990s): digital signals to carry voice with limited data
3G & 3.5G (2000s): addition of higher-speed data
4G (2008): focuses on real-time multimedia
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Cellular Standards
European: TDMA technology called Global System for Mobile Communications (GSM)
Motorola: TDMA technology called iDEN
Japan: TDMA technology called PDC
Source: Douglas, C (2016) Computer Networks and Internets
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Cellular Services
General Packet Radio Service (GPRS) & Wireless Application Service (WAP): Internet access
Enhanced Data rate for GSM Evolution (EDGE) & Enhanced GPRS (EGPRS): higher rates
EDGE Evolution: even higher rates
Short Message Service (SMS): textual messaging
Multimedia Messaging service (MMS): multimedia messaging
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Practice 18.2
Explain the THREE (3) building blocks of WLAN.
What are the TWO (2) possible WLAN configurations?
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Lesson 18 Outline
PAN Technologies
LAN & MAN Technologies
WAN Technologies
Cellular Technologies
Satellite Technologies
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Parabolic Antenna
Key to satellite communication is a parabolic antenna (dish)
Aiming dish at satellite and placing detector at focus point guarantees strong signal
Incoming energy is reflected from dish towards receiver
Source: Douglas, C (2016) Computer Networks and Internets
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VSAT Satellite Technology
Very Small Aperture Terminal (VSAT) satellites use three frequency ranges that differs in
Strength of the signal delivered
Sensitivity to atmospheric conditions
Satellite footprint
Source: Douglas, C (2016) Computer Networks and Internets
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GPS Satellites
Global Positioning System (GPS) satellite provide location-based services
Obtaining position is straightforward: receiver can determine location on earth by calculating distance to the satellites
Source: Douglas, C (2016) Computer Networks and Internets
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GPS Process
Source: Douglas, C (2016) Computer Networks and Internets
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Reading
Douglas, C. (2016). Computer Networks and Internets, Global Edition (6th ed.). Pearson Education. ISBN: 978-1292061177 Chapter 16
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End of Lesson
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