CCIT4085

Information
Technology
Fundamentals

3.1 - Communication, Network and Internet

24-25s1
Communication, Network and
Internet
▪ Communications
▪ Different Types of Networks
▪ Transmission Speed
▪ Transmission Media
▪ The Internet
▪ IP Address and Domain Name
▪ Network Security

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Communications
▪ There are five components that are necessary for communications:
sending device, communication device (sender side),
communication channel, communication device (receiver side), and
the receiving device.
▪ The function of the sending/receiving device is to generate/receive
data or information.
▪ The function of the communication device, at the sender side, is to
convert the original information into the form that can be
transmitted through the communication channel; and at the
receiver side, is to recover the original form of the information so
that the receiver can understand the information.
▪ The communication channel is the place in which the data,
information, or signal can travel through from one side to the other
side.
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Communications -
Computer Networks
▪ PC network card (chip) cable network card (chip)
PC

• The two PCs are the sending/receiving devices.

• The original information are in binary form. In order to transmit
those through many different kinds of network links (wired or
wireless), a network card (chip) is needed to first convert the
binary signal into analog signal at the sender side.
• The analog signal then travels to the receiver side through
network links.
• At the receiver side, the network card (chip) can convert the
analog signal back to binary signal and the receiving PC can
get the file.

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Communications - Telephone
Networks (extra)
▪ person (mobile) phone air (mobile telephone network)
(mobile) phone person

• The two persons are the sending/receiving devices.

• The original form of information is speech. A phone converts
the speech into electronic signals at the speaker side and then
another phone converts the electronic signals back to speech
at the listener side. The channel can be wired or wireless.

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Communications -
Traditional Television
Broadcast (extra)

▪ machine with TV programs → transmitter → air (radio network)

→ TV (receiver) → person

• The original information are TV programs, the transmitter

converts TV programs into radio signals and the TV at home
converts the signals back to video. The communication channel
in this case is the air (or cable).The communication is one-way.
• In many other communication cases, we can also identify
these five components.

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Computer Networks
• Computer network is a collection of computers or devices
connected together via communications devices and transmission
media. For computer networks, the transmission media are
(equivalent to) the communication channels.
• The purpose to setup a computer network is mainly to share
resources, e.g., hardware, software, data, and information.

A computer network sharing printer and scanner

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Computer Networks
• Based on different sizes, computer networks can be:
• PAN personal area network, network organized around an
individual person typically involve a mobile computer, a cell
phone and or a PDA.
• LAN local area network, network in limited geographical areas
such as home or office building.
• MAN metropolitan area network, connects LANs in a city.

• WAN wide area network, network that covers large geographic

area using many types of media, e.g., the Internet.

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Computer Networks

Scale of coverage in computer networks

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Computer Networks (extra)
• Traditionally, LANs have different shapes or layouts. The shape of
a network is called the network topology.
• Common topologies are bus network, star network, and ring
network. Also, we can have mesh network and tree network. Star
network is most popular nowadays.
• For larger networks such as MAN and WAN, it is hard to define
their shapes.

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Computer Networks (extra)

Network topologies

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Computer Networks
• Based on communications channel (media), computer
networks can be wired or wireless.
• In both wired or wireless networks, there are many different kinds
of technologies to define the cabling, the connection methods, as
well as how data are sent.
• Some common networking technologies are:
For wired: Ethernet;
For wireless: WiFi, Bluetooth, IrDA, and broadband cellular
network (3G, 4G, 5G).

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Computer Networks (extra)

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Local Area Network

▪ Local Area Networks (LAN) is widely used to share resources and

exchange information. It is a network that is limited to an area
such as a building or school. In a LAN, computers and hardware
such as printers can be connected by cable (e.g. copper wiring),
or using a wireless (e.g., Wi-Fi) connection.

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Local Area Network
▪ Devices such as computers, servers and printers can communicate with
each other by using their own private Internet Protocol (IP) addresses
within the LAN. When the devices want to communicate with other
device outside the LAN, their IP addresses are needed to replace by
the public IP addresses. This IP address replacement is done at the
gateway router.

Gateway Router

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Computer Networking Demystified – WordPress.com

Client and Server
• Servers are hosts that have software installed that enable them to
provide information, like email or web pages, to other hosts on the
network.
• Clients are computer hosts that have software installed that enable
them to request and display the information obtained from the
server.

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Transmission Media and
Transmission Speed
• Transmission media are the media in which data, instructions, or
information travel in computer networks
• The transmission speed of a kind of transmission medium is
called bandwidth of the medium (the channel), and is measured in
terms of bit per second (bps). Some common units are Kbps,
Mbps, and Gbps.
• 1Kbps = 1000bps, 1Mbps = 1000Kbps, and 1Gbps =
1000Mbps.
• Bandwidth is the maximum amount of data that can travel over a
communication channel per time unit.
• While the actual amount of data can be transmitted per time unit is
called the throughput of the channel.

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Transmission Media
• Cables (physical transmission media):
• Twisted-pair cable

• widely used for network cabling and telephone system

• Two separate insulated copper wires that are twisted together
• Coaxial cable

• often used in cable television

• consists of a single copper wire surrounded by at least three
layers
• Fiber-Optic cable

• Consists of hundreds of thin strands of optical fiber (as thin as

human hair
• Fast, better security, small size, less noise, but more expensive

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Transmission Media (extra)

Twisted Pair cable

(0.4Mbps to 10 Gbps)

Coaxial cable
(10Mbps to 1.5Gbps)

Fiber-Optic cable
(up to 255Tbps)

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 Transmission Media (extra)
▪Wireless media:

Transmission media Maximum transfer rate

Infrared 1Gbps
Broadcast radio • Bluetooth 24Mbps
• Home RF 10Mbps
• WiFi 802.11n 600Mbps
• WiFi 802.11ac 3.5Gbps
• WiFi 802.11ax 9.6Gbps
• WiFi 802.11be up to 46Gbps
Cellular radio • 3G 2.4Mbps
• 4G LTE download: 300Mbps; uplink 75Mbps
• 5G 3.2Gbps to 10Gbps(in future)
Microwave radio 500Mbps
Communication satellite 134Gbps+

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The Internet
▪The Internet is the largest (logical) network in the world. We can simply
consider the Internet is formed by connecting a huge number of different
kinds of networks and computers all over the world.
▪No single person, company, institution, or government controls or even
owns the Internet.
▪The World Wide Web Consortium (W3C) oversees research and sets
standards and guidelines for many areas of the Internet.
▪In the Internet, many companies, organizations, and personals provide
many different kinds of services to other Internet users, for example, web
mail, file transferring, messaging, gaming, news, Internet telephony,
discussion forums, shopping, auction, virtual community, map, etc.

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The Internet
▪ You can connect to the Internet in many ways: Dial-up line or broadband
service (through telephone network, cable TV network, power line, or
wireless) at home, or the "always on“ connection at school/work.

Dial-up service Broadband service

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Common Internet Services
▪ World Wide Web (WWW), or the web, is a worldwide collection of electronic
documents.
▪ Each document is called a web page. A web page can contain text, graphics,
sound, video, etc. Web pages often are prepared by HyperText Markup
Language (HTML).
▪ A computer is called a web server (host) if it provides place for users to store
their web pages and allows others in the Internet to download those web
pages.
▪ A collection of web pages in a web server is called a web site. Web pages in
the same web site often are related and connected through hyperlinks.
▪ Users access web sites through programs called web clients or
web browsers. Common ones are Chrome, Safari, Firefox, Edge, Opera. To
download a web page or a file, a web client uses the HTTP protocol.

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TCP/IP Protocol Suite
▪A protocol is a set of rules for the two communication parties to follow.

▪Because there are so many different computers connected to the Internet, and
the computer may use different kinds of networking technologies, in order to let
all the (different) computers in the Internet to communicate, there must be
something in common to all the computers.
▪Such common thing (technology) for the Internet is the TCP/IP protocol suite.

▪TCP/IP stands for Transmission Control Protocol and Internet Protocol. They
are the most well-known representatives from a collection of protocols used in
the Internet.

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TCP/IP Protocol Suite (extra)
▪For example, TCP/IP defines how to divide a large file into some small pieces
called packets, how to identify a computer in the Internet (addressing), how to
find a path and forward the packets to the correct computer (routing and
forward),etc.

Packets are relayed through routers

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TCP/IP Protocol Suite (extra)
▪Some common (application level) protocols and their purposes are:

▪HTTP - HyperText Transfer Protocol is used to transmit web page in

the web service.
▪FTP - File Transfer Protocol is used to upload/download files in the file
transferring service.
▪SMTP - Simple Mail Transfer Protocol is used to send out email
messages in email service.
▪POP - Post Office Protocol is used to receive email messages
in email service.
▪others are NNTP for newsgroup, Telnet for remote access, etc.

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IP Address and Domain Name
• In order to find a computer on the Internet, each computer connected to
the Internet must have some kind of identity, or name, or address.
• Such an address is called the Internet address or IP address.

• It consists of 32 bits and is represented in a dot-numeric format: e.g.,

147.8.162.111, 192.168.8.59, etc.

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IP Address and Domain Name

IP address of desktop IP address of mobile phone

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IP Address and Domain Name
• The numbers are divided into four groups by 3 dots. Each number
ranges from 0-255 (for the reason of 8 bits), so totally we have four
numbers each ranges from 0-255 (for the reason of 32 bits).

IPv4 Address format

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IP Address and Domain Name
(extra)
• IPv6 is the new version of the Internet address protocol that has been
developed to supplement (and eventually replace) IPv4, the version that
underpins the Internet today.
• IPv6 addresses are 128 bits long

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Decomposition of an IPv6 address into its binary form
IP Address and Domain Name
• IP addresses are mainly for machines. In order to let us easily memorize
a computer, domain names of computers are used.
• You can consider a domain name as the text version of the address of a
computer. Besides the (leftmost) computer name, all other parts are
called domains
• For example, http://www.example.net
• Domain name: example.net

• Top level domain name: net

• Second level domain name: example

• Host name: www

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IP Address and Domain Name
• More examples of domain name

• hk, hku.hk, com, yahoo.com

• We usually call the rightmost domain the top level domain.

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 Uniform Resource locator
(URL)
• To access a web page (or any Internet resource), a user must provide
the URL of the page to the client.
• URL stands for Uniform Resource Locator. It is a format of address for
us to identify (locate) an object in the Internet.
• Each URL usually contains four parts, namely, the method (protocol) to
access the object, the host (machine) where the object is in, the path in
the machine where the object is stored, and the name of the object. E.g.

http://www.hku.hk/about/uid/introduction.html

Method (Protocol) name of the object

Host and domain name Path
(web page)
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Network Security
• Because more and more personal as well as commercial activities
involve computers and the Internet, the security issues of computers
and networks become more and more important.
• Computer and network security address the issues of how to prevent the
others from illegitimately accessing, using, or damaging your computer
or network resources.
• The resources can be computers (both hardware and software, e.g.,
CPU time), (rights to access) network resources (users’ personal)
information or files stored in computers, etc.

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Security Threats
• Sniffing

• capture and analyze packets (e.g. password, account no.) in a network.

• Spamming

• Use of electronic messaging systems to send unsolicited messages

(especially junk email). Spam messages can contain links that when
clicked on could go to a website that installs malicious software onto
your computer.

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Security Threats

• Phishing

• often pretend to be a trustworthy entity in electronic communication.

• use some "good-looking “information to trick users’ personal information

• E.g. fake emails, social profiles, websites, and phone calls

• Bandwidth Piracy

• gain free access to the Internet by connecting to other users’ network.

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Security Strategies
• To reduce the risks of the attacks, some security strategies should be
adopted in managing computer systems or networks to protect the
confidentiality, integrity and availability of the data.
• Common security strategies: antivirus, encryption, access control, and
authentication.

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Security Strategies – Antivirus
software
▪ To detect and prevent malware attacks, we should install antivirus
software.
▪ Examples: Norton Antivirus, McAfee, Bitdefender, Kaspersky, Avast

▪ For an infected machine, antivirus can scan viruses and other

malware, then remove them, or quarantine the infected files.

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Security Strategies –
Encryption
▪ Personal or system information can be protected through encryption.

▪ To encrypt is to scramble and convert the original data or information

into an unintelligible and meaningless form.
▪ To decrypt a file, one needs to provide a piece of data correctly, and the
piece of data is usually called the encryption key.

Public key encryption and decryption

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Security Strategies – Access
Control
• Another common security strategy is access control, which determines
and enforces who or what can gain access to the computer systems or
networks.
• To enforce access control, users can setup username and password
combinations to protect the accounts, computers, or network.

• To access others’ account, computers,

or network without
permission is called unauthorized
access.
• Persons who perform unauthorized
access can be considered as hackers.
Today, unauthorized access is
considered as a crime.
A login page for access control
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Security Strategies – Access
Control
• Further, users can setup hardware or software firewall to filter both
incoming and outgoing traffic.
• Intrusion detection software can also be used to monitor and analyzes
incoming and outgoing traffic of computers and network, or activities of
file access (read and write operations in storage) so that suspicious
behaviors can be identified.

• A typical network where firewall and intrusion detection system are

deployed.
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Security Strategies –
Authentication
• A higher level of security strategy is authentication, which verifies a
person’s identity (i.e., proving a user is the claimed user) before allowing
computer or network access.
• The rational behind authentication is that a correct password does not
automatically indicate an authorized user.
• Some authentication methods are token-based authentication, biometric
identification, and digital certificates.

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Security Strategies –
Authentication
• In token-based authentication, a user is given a unique token (such as a
security code generator used in banking), then besides the correct
password and username, the user also needs to provide a correct one-
time password generated by the token in order to gain access to the
systems.

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Security Strategies –
Authentication
• Biometric devices use human intrinsic characteristics to authenticate
users. There are two main types of biometric authentication:
physiological and behavioral.

The two main types of biometric authentication

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