Transcript Communication and Network - International University of Japan

Communications and
Computer Network
Hun Myoung Park, Ph.D.,
Public Management and Policy Analysis Program
Graduate School of International Relations
International University of Japan
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Outline
Communication Basics
Analog versus Digital
Frequency and Bandwidth
Transmission Types
Telecommunication Media
Network Typologies
Type of Network
Network Data Security
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Communication Basics 1
Sender encodes (converts) his message.
Receiver decodes (translates) the received
message.
Message to be sent
Media or channel through which the
message travels (air, radio, TV, phone,
Internet, etc.)
Feedback (error checking)
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Communication Basics 2
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Analog vs. Digital Signals
Analog signals: continuous
o Frequency
o Amplitude
Digital signals: discrete
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Modem 1
Modem (modulator/demodulator)
o Converts analog signals to digital ones
(modulation) and vice versa
o Dial-up connection
o Bps (bit per second)
o Baud (pulses per second) or modulation rate
o Emulation software: check errors (parity bit)
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Modem 2
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Frequency
Frequency (Hz), the number of times a signal
makes a complete cycle per second. KHz,
MHz, GHz
Wavelength: from long (low frequency) to
short (high frequency—UHF, cell phone).
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Bandwidth
Bandwidth (bps) is ranges of frequencies.
The difference between the highest and
lowest frequency transmitted (or amount of
data transmitted) per second.
Bps, Kbps, Mbps.
Baud (pulses per second) or modulation rate
Broadband has a rate of greater than 1.5
Mbps (telephone).
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Transmission Types
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Transmission Types 1
Serial versus parallel transmission
Wired (faster and more secure) versus
wireless (electromagnetic radiation) network
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Transmission Types 2
Direction of transmission:
o Simplex: transmitted in a single direction only
o Half-duplex: one direction at a time
o Full-duplex: both directions at the same time
Timing of transmission
o Synchronous: blocks of data are transferred
o Asynchronous: start and stop bits to distinguish
one byte from the others (e.g., email).
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Telecommunication Media
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Media 1
Twisted-pair wire: pairs of copper wire. IEEE
802 standards of RJ-45 (LAN) and RJ-11
(Telephone)
Coaxial cable (coax) in the cable TV industry.
Inner conductor. More expensive, faster, less
susceptible to interference (by shield
blocking electro-magnetic signals)
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Media 2
Optical fiber cable uses light pulse sent by a
laser device thought the strands of glass.
Thin coating “cladding” prevents the light
from leaking out of the fiber.
Super-fast and in turn expensive.
Used for backbone (telephone) network.
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Media 4
Us of wireless media is often regulated
Radio frequency (RF) transmission: 3kHz300MHz
Microwave (“line-of-sight”): communication
satellite use microwave stations (microwave
antennas) and satellite dishes. 300MHz300GHz
Infrared (IR) transmission: 300GHz-400THz
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Media 5
Cellular radio: cell, cellular tower, mobile
telephone switching office (MTSO). G3.
Global positioning systems (GPS),
Bluetooth, infrared transmission, near field
communication (NFC) : short range
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Network Channel 1
Telephone lines
o Conventional dial-up connection
o ISDN (Integrated Services Digital Network)
o DSL (Digital Subscriber Line) uses higher frequency
than voce phone call on telephone lines.
o DSL splitter separates digital and analog signals
o ADSL (Asymmetric DSL)
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Network Channel 2
Cable access (cable TV).
Satellite and fixed wireless access need
modems and transceivers.
Wired Ethernet
o Bell Lab’s T1 (1.5Mbps), T3 (44.7Mbps)
Broadband over fiber (BoF)
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Network Channel 3
Cellular broadband or mobile wireless
(laptops, smart phones)
o Wi-Fi (Wireless Fidelity) is wireless networking
standards (wireless Ethernet)
o IEEE 802.11
o 802.11a, …802.11g, 802.11n
o 802.11ac (2.4 GHz or 5.0 GHz)
 3G, 4G, 5G, LTE (Long Term Evolution)
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Network Typology
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Network Topology 1
Star network has a central hub (router)
connected by other devices.
Ring network: devices are connected from
one node to the next. One-way direction of
transmission. IBM’s Token Ring Network
Bus network has a central bus line to which
devices (nodes) are attached.
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Network Topology 2
Mesh network: each device is connected to
multiple devices in a network.
Hybrid network combines above typologies.
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Type of Network
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Types of Network 1
Sharing programs, data, and devices
Access to databases and better security
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Types of Network 2
LAN (Local Area Network)
o Covers small geographical area
o Bridge for same types of networks
o Router for different networks (layer 3)
o Gateway, bridge + router + etc.
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Types of Network 3
WAN (Wide Area Network)
MAN (Metropolitan Area Network)
VPN (Virtual Private Network) allows remote
and secure access to the network (intranet)
through encrypted “tunneling”
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Types of Network 4
Intranets versus extranets
o private networks used for employees.
o Authorized outsiders can access extranets.
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Client-server Network
Servers process clients’ request and provide
services to clients. Not particular machines
but functions.
Depending on tasks, network, file, mail, Web,
DNS, printer, license servers and others are
available.
A single machine can run more than one
servers.
Uploading and downloading (polling &
addressing)
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Peer-to-peer Network
Direct access to other devices without
central (in classical sense) servers.
P2P servers mange indexes, not contents to
bridge users.
Internet P2P computing for sharing resources
online. But it often infringes intellectual
property rights.
Suck down all available resources on the
network, resulting in network congestion
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Network Hardware 1
Modem and cable modem
Gateway is an entrance to another network
Wireless access point and hot-spot
Private Branch Exchange (PBX)
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Network Hardware 2
Router forwards data packets between
computer network (layer 3-network). IP
address is used.
Network switch (switching hub, bridging hub)
contains ports to which all the devices
(nodes) on the network can connect (layer
2-data link). Only one broadcast domain.
MAC is used.
http://www.diffen.com/difference/Router_vs
_Switch
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Network Data Security
Encryption converts an original message into
a form that can be understood only by the
intended receiver
Encryption key is applied to a set of
unencrypted text to produce encrypted text
Encryption algorithm: symmetric versus
asymmetric algorithm. RSA is a symmetric
algorithm for public-key cryptosystems
Wireless Protected Access 2 (WPA2)
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Virtual Private Network
“Extends a private network across a public
network” (Internet) to allow remote users to
send and receive data as if they are directly
connected to private network.
Establish a virtual point-to-point connection
through tunneling protocols.
Support secure, encrypted connections
between a company’s employees and
remote users
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References
Stair and Reynolds. 2016. Principles of
information systems, 12th ed. Cengage
Learning.
Stair and Reynolds. 2012. Information systems,
10th ed. Cengage Learning.
Morley and Parker. 2015. Understanding
computers, 15th ed. Cengage Learning.
Hutchinson and Sawyer. 2000. Computers,
Communications, and Information, 7th ed.
Irwin/McGraw-Hill