SEE COMPUTER SCIENCE 2079
(1.1.1) Introduction to Networks
(i) Communication Media (Guided & Unguided Media)
(ii) Elements of Network (NIC Card, Connectors, Hub,
Bridge, Switch, Router, Gateway, Repeater, Modem)
(iii) Types of Network
LAN, MAN, WAN
(iv) Network Architecture
Peer-to-peer Network, Client-Server Network,
Centralized Network
(v) Topologies (Bus, Star, Ring)
(vi) Protocols (Definition and Example only)
(vii) Advantages & Disadvantages of Network
(viii) Internet and its services
1.1 Networking &Telecommunications
Data Communication
Data communication is the process of transferring data and information
between
computers and other electronic devices..
Eg.
E-Mail, Radio and phone calls.
There
are two types of communication mode:
i)
Simplex mode ii) Duplex mode
Simplex
mode
Simplex mode is the transmission of data and information
that takes place in only one direction.
It is a unidirectional mode of data transmission.
Radio, newspaper, television broadcasting, books etc. are
examples of simplex mode.
Duplex mode
Duplex is
mode of data transmission in which data and information flow in both directions.
It is
bi-directional mode of data transmission.
The two
types of duplex modes are:
i)
Half Duplex mode ii) Full Duplex mode
Half
duplex mode
Half duplex is the mode of data transmission in which
data and information flows in both directions but only one direction at a time.
Walky-talky
and wireless handset are examples of half-duplex mode.
Full
duplex mode [MF 2076]
Full duplex is the mode of data transmission in which
data and information flow in both direction simultaneously.
Mobile and landline phones are examples of full duplex
mode.
Components of Data Communication.
i)
Data ii)
Sender iii) Medium
iv)
Receiver v) Protocol
Transmission medium / Communication
Channel
A channel or
path through which data and information are transmitted between connected
devices in a network environment is called communication
media.
The
types of communication medium are:
1. Guided (Wired/bounded)
communication media
2. Unguided (Wireless/unbounded) communication media
Guided medium
The media
which uses cable or wire to transfer data and information among computers
are called guided communication media.
It is an
easy, fast and secure way to transfer data and information from one computer to
another.
The three
types of guided media are:
a. Twisted
pair Cable
b. Co-Axial
Cable
c. Fiber
Optic Cable
Features of guided media:
-
Data transmits through the physical cable or fixed path
-
Data transmission rate is higher.
Twisted pair cable
A
set of four pair of wires twisted with each other is known as twisted pair
cable.
Wires
are twisted with each other so as to reduce crosstalk (A disturbance caused by electromagnetic interference, along a circuit or
a cable pair).
RJ-45 connector is the most popular connector used in twisted-pair wire.
Its
types are:
a)
Unshielded Twisted Pair (UTP)
b)
Shielded Twisted Pair (STP)
Co-axial cable
Coaxial cable is a common type of cable used for
transmitting data over long distances.
They are most commonly used to transmit cable TV and Internet
signals.
The connectors used with co-axial
cables are BNC, T-connectors and terminators in bus topology.
Fiber optic cable
Fiber optics cable is one of the
costlier cables used in data communication which uses light to carry a data
signal through the cable.
The connectors used in fiber optics
are Screw Mounted Adaptors (SMA), Spring-loaded Twist (ST), SC and FC.
Unguided medium [SEE 2074 U]
The transmission media which transfer data in the form of
electromagnetic waves that do not require any cables for transmission is called
unguided medium.
E.g.:
radio wave, microwave, satellite communication etc.
Radio wave transmission
· The transmission
making use of radio waves through air is called radio wave transmission.
· It provides low
bandwidth for data communication.
· Radio,
TV, cellular phones etc. uses radio transmission in one form or another.
· The
radio waves can travel through walls and through an entire building.
· It does not require line of sight for data transmission
Microwave transmission
· Microwave is
a line-of-sight wireless communication technology that uses high
frequency beams of radio waves to provide high speed
wireless connections that can send and receive voice, video, and data
information.
· Microwaves
do not pass through buildings. So, indoor receivers cannot be used effectively.
· It provides
higher bandwidth for data communication.
· It requires line of sight for data transmission.
Satellite Communication
·
Satellite Communication is defined as a type of communication where the
exchange of information takes place between different stations present on the
surface of the earth using artificial satellites in space.
·
Through satellite communication,
data, voice, audio, video signals can be transmitted and received by using
communication links between various regions of the earth.
Computer network
Computer
network is a group of two or more computers and devices connected to each other
through wired or wireless media to exchange data and information and share hardware,
software and other resources.
Advantages of computer network
· It can share hardware devices such as scanner, printer, hard disk, etc.
· It can communicate and share information all over the world through
Internet.
· It supports centralized administration.
· It provides the facility of data and software backup system.
Disadvantages of computer network
· Computer network can be route for computer virus and malware transmission.
· Skilled manpower is required to manage and operate computer network.
· The initial setup cost is very high to build computer network.
· Cybercrimes are originated from computer network.
Basic Elements of the Network
Physical
parts and devices used to connect computers in the network environment are
called hardware components.
The
hardware components of computer network are computer set,
modem, hub, NIC card, bridge, repeater, etc.
The
software elements are NOS, Protocol and Device Driver
NIC Card (Network Interface Card)
A
Network Interface Card (NIC) is the hardware component through which the
computer is connected to the network.
The
function of NIC is to control flow of data to and from computers in network
environment.
Connector
Connector is
a device that facilitates the connection of computers and other device to a
network.
Examples of connectors are BNC used
with coaxial cable, RJ 45 used with UTP cable, ST used with fiber optic cable
etc.
Hub
Hub is a
network connectivity device with multiple ports for connecting different computers
on network.
It broadcasts all network data across each connection.
Hub is mostly used in physical star
topology.
Switch
Switch is a network connectivity device which joins
multiple computers together to share information among them.
The selected
computer can get information through switch.
It works
faster than hub.
Hub Vs Switch
|
Hub |
Switch |
|
It is cheaper than switch. |
It is more expensive than hub. |
|
It transmits data slower than switch. |
It transmits data faster than hub. |
|
It broadcasts the information packets to all computer connected network. |
It transfers packets to only those selected computers connected in network. |
|
It has 4 / 12 ports |
It has 24 to 48 ports |
Bridge
Bridge is a
network connectivity device that interconnects two computer networks having
similar protocol.
It inspects
incoming signals and decides whether to forward or discard it.
Router
Router is a network connectivity device that joins multiple wired or
wireless networks together.
It also inspects and forwards
data among different networks having similar protocol like bridge.
It is an intelligent device
that has ability to determine the best possible path for data transmission.
Gateway
Gateway is a network connectivity device that
interconnects two networks having dissimilar communication protocols.
Repeater
Repeater is a network connectivity device that accepts weak signals and
regenerates
them and after that sends the
message on their way.
It makes possible for
long-distance
data transfer. So it boosts the data signals that are received from
network.
MODEM (Modulator and Demodulator)
MODEM
is a device which is used to transfer the data of one computer to another
computer using telephone lines.
Importance of MODEM [ 2071 S] 2073 U]
MODEM
modulates the digital codes of the computer into analog signal, which then can
travel through the telephone cable.
At the receiving
end the MODEM kept there will demodulate the analog signal to digital codes,
which can be then understood and used by the receiving computer.
Modulation
The process of
translating digital signals of a computer to analog signals, which are then
transmitted across the standard telephone lines, is known as modulation.
Demodulation
The process of
translating analog signals from a phone line and converts then into digital
signals for the computer is known as demodulation.
Bandwidth
The amount of data that can be carried from one point to another in a given
time period is called bandwidth.
We can measure
bandwidth in digital devices by bits per second (bps) and in analogue devices
by cycles per second (cps) or Hertz (Hz).
Network operating system (NOS)
Network operating
system is a software which control and manages computer network.
E.g. Novell
Netware, Windows NT, Linux, Unix etc. The main functions of NOS are:
·
It enables users to have access to network resources.
·
It manages and controls all the resources of computer
network.
Protocol
[MFT 2075]
A set of rules followed for interconnection and communication between
computers in a network is called a protocol.
Some common protocols are as
follows:
·
TCP/IP (Transmission Control Protocol/Internet Protocol)
is used in Internet.
·
HTTP (Hypertext Transfer Protocol) is used to transfer
HTML documents in
·
WWW.
·
SMTP (Simple Mail Transfer Protocol) is used in sending
e-mail.
·
POP (Post Office Protocol) is used to retrieve e-mail
from a mail server.
·
FTP (File Transfer Protocol) is used to transmitting
files between computers.
Device driver
Device driver is a
program that controls the functionality of the hardware device.
Types of Network
a)
LAN
(Local Area Network)
b)
MAN
(Metropolitan Area Network)
c)
WAN
(Wide Area Network)
LAN (Local Area Network)
Local Area
Network is a network that connects a group of computers in a small geographical
area like a room, a building, school, etc.
Computer in
LAN can be connected through wireless media and is referred to as WLAN
(Wireless Local Area Network).
Computer lab
networking and cyber networking are examples of LAN.
Features of LAN
·
It can cover up to one kilometre for transferring data
and information between the computers.
·
It is normally owned by single organizations.
·
It has high speed data transfer capacity than MAN and
WAN.
·
LAN supports a variety of communications transmission
medium such as an Ethernet
cable (thin
cable, thick cable, and twisted pair), fiber and wireless transmission.
MAN (Metropolitan Area Network)
Metropolitan Area Network (MAN) is a network
of computer spread over a city or town located in the same geographical area
It is used in medium size organization having various branches within city
or valley.
Cable TV network and branches of banks are examples of MAN.
Features of MAN
· It can cover up to fifty kilometre for transferring data and information
between the computers.
· It is normally owned by single or multiple organizations.
· It has high speed data transfer capacity than WAN and is slower than LAN.
· Fiber optical
cable and twisted pair cables are used for connectivity for communication
through MAN networks.
WAN (Wide Area Network)
A wide area
network (WAN) is a computer network that covers a large geographical area
comprising a region, a country, a continent or even the whole world
It is the
largest computer network.
Internet, 4G
Mobile Broadband Systems and satellite communication are the best examples of
WAN.
Features of WAN (Wide Area Network)
·
It covers the whole world and cannot be restricted to any
geographical location.
·
It is normally owned by multiple organizations.
·
They have low data transfer rate and have low
communication speed.
·
It uses satellite and microwave communication.
Network architecture (Models of Computer
Network)
Network
architecture can be defined as how the computer communicates and interacts with
each other on network.
Its types are
a)
Centralized
computing network
b)
Client
/ Server Network
c)
Peer
to Peer Network
Centralized network
A
centralized network is a network in which a central host computer performs data
processing and storage on behalf of clients.
The main
computer is known as host or server computer.
Workstation is
just used for input/output operations, which has no processing capabilities and
are connected to server or host computer. Linux or UNIX operating system is
used in
centralized
network.
Client/server network
Client/
server network is a type of network model where at least one computer is
designed as a server and other computers on the network called clients or
workstations.
It
provides central security administration and the network administrator is
responsible for data security and other resources management of the network.
Peer-to-peer network
Peer-to-Peer network is a type of
network model where all the computers have equal responsibilities on the
network.
It lacks centralized network
administration, where the network administrator needs to manage security on
each computer.
It provides no reliable security and
might put data in higher risks.
Server
A
server is the main computer that provides services, data and other resources to
the other computers in the network environment.
Workstation
A
computer on a network that uses resources of the network is called workstation.
Node
Each
computer or device of network is called node.
Network topology (LAN topology)
Network
topology is the cabling structure of interconnected computers in LAN.
The
three basic topologies are bus topology, ring topology and star topology
Bus topology
The network topology in which nodes and network devices are connected to a
single cable is called bus topology.
Advantages of bus topology
a)
It
is cost effective and cable required is least compared to other network
topology.
b)
It
is easy to expand network.
Disadvantages of
bus topology
a)
Break/Failure
in main cable will make the whole network to malfunction (failure).
b)
Heavy network traffic or increase in nodes will degrade
performance of network.
Diagram of bus topology
Ring topology [MF 2076]
A
ring topology is a network topology where all the nodes on the network are
connected to each other in the form of ring or circle without any end points.
The
method by which data is transmitted around the ring is called token passing.
Advantages of ring topology
· Each computer
gets equal opportunity to access the network resources.
· Transmitting network is not affected by high traffic or by adding more
nodes.
Disadvantages of ring topology
·
Adding or deleting the computers disturbs the network
activity.
· Failure of one computer disturbs the whole network in this topology.
Diagram of ring topology
Star topology
The network topology which connects all nodes to central device called hub/switch through a
cable is
called star topology.
Advantages of star topology
·
It provides fast performance and low network traffic.
· The failure of one node does not affect the rest of the nodes.
Disadvantages of star topology
·
Hub and more wires are required, so the cost of
installation is high.
·
The whole network is stopped when the hub fails.
Diagram of star topology
Internet
(Network of Networks)
The internet is the largest computer network that
connects millions of computers around the world.
Services of internet
a)
WWW
(World Wide Web)
b)
E-mail
(Electronic mail)
c)
FTP
(File Transfer Protocol)
d)
IRC
(internet Relay Chat)
e)
Telnet
f)
Search
Engine
g)
Online
Banking
h)
E-Commerce
Advantages
of internet
a) Greater access to
information reduces research time.
b) Global reach enables one to
connect to anyone on the internet.
c) Selling and buying has
become so easy with the use of internet and it has helped millions to sell and
buy their goods online.
d) Easy communication with
other people.
Disadvantages
of internet
a) Computer viruses get downloaded and spread
across machines connected to networks and have harmful effects.
b) People using too much of
internet get disconnected from the real world.
c) Pornography can get in the
hands of young children too easily.
d) Cyber frauds may take place
involving Credit/Debit card numbers and details.
Intranet
An
intranet is a private computer network that uses the internet protocol to
securely share any part of information of an organization.
It
is owned by a single organization or company.
It
can only be used by the employees of the owned organization.
Extranet
An
extranet is a private network that uses internet technology and the public
telecommunication system to connect more than one organization.
ISP
(Internet Service Provider)
An Internet service provider (ISP) is an organization that
provides services for accessing and using the Internet.
World
Link, Mercantile, Classitech, Vianet etc are the ISPs of Nepal.
E-mail
(Electronic Mail) [SLC 2068 S] [SLC 2069 S] [SEE 2075 S2] [MM 2076] [MFT 2075]
E-mail
(Electronic mail) is one of the most popular services provided by the internet sends and receives messages electronically through the Internet.
E.g.
xyz@gmail.com
Any four sites that provide e-mail services are:
Advantages of E-mail
·
It is the cheapest and fastest means of communication.
·
It is more reliable than postal mail.
·
E-mail can be accessed from any part of the world at any
time.
·
Information can be shared globally.
·
We can send photos, songs, video clips and other file
with e-mail attachments.
· A single mail can be sent to multiple people at a time.
Disadvantages of e-mail
·
The
recipient needs access to the internet to receive email.
·
Viruses are
easily spread though email attachments.
Telnet
Telnet is the facility of Internet that allows user to
use a remote computer through Internet.
FTP (File
Transfer Protocol)
File Transfer Protocol (FTP) is transmission files
between computers on the Internet.
File
Transfer protocol helps to transfer (download or upload) files from one
computer to another computer.
Uploading
Ans: Uploading refers to copying files or documents, programs or data from the
user’s computer to the internet server.
Downloading
Downloading refers to the copying files or document or program or data from the
internet server to the user’s computer.
Web browser
Web browser is a computer program that access web pages and displays them on
the user’s computer.
Examples of web browsers are Mozilla
Firefox, Google chrome, Internet Explorer, opera etc. Browsing/
Surfing means searching information on the internet.
Search engine
[SEE 2074 U] [SQE 2075K]
A
search engine is a service of internet that helps allows the users to find
the information on the World Wide Web using keywords or phrases.
Examples of search engines are
Google, Bing, Yahoo etc
Full
Forms
NCC - National Computer Center
EDP - Electronic Data Processing Center
RJ-45 – Registered Jack 45
UTP - Unshielded Twisted Pair
Mbps -
Megabits per second
STP - Shielded Twisted Pair
EMI-
Electromagnetic Interference
BNC –
British Naval Connector
ISP –
Internet Service Provider
ST –
Straight Tip Connector
SMA – Screw
Mounted Adaptor
SC –
Subscriber Connector
FM –
Frequency Modulation
AM –
Amplitude Modulation
PM – Phase
Modulation
NOS –
Network Operating System
NIC –
Network Interface Card
LAN – Local
Area Network
IP –
Internet Protocol
MODEM –
Modulator and Demodulator
bps – bits
per second
NCP –
Network Control Protocol
TCP/IP - Transmission
Control Protocol/Internet Protocol
HTTP - Hypertext
Transfer Protocol
SMTP –
Simple Mail Transfer Protocol
POP – Post
Office Protocol
FTP – File
Transfer Protocol
MAN
-Metropolitan Area Network
WAN - Wide
Area Network
WLAN -
Wireless Local Area Network
IPOS - Input
Process Output System
ARPANET - Advanced
Research Projects Agency Network
WWW – World
Wide Web
URL –
Uniform Resource Locator
E-mail –
Electronic Mail
IRC – Internet
Relay Chat
B2B - Business
to Business
B2C - Business
to Customer
C2C – Customer
to Customer
C2B - Customer
to Business
ATM – Automated
Teller Machine
E-Commerce –
Electronic Commerce
E- fax – Electronic
Fax
FAQ – Frequently Asked Questions
SIM - Subscriber
Identity Module
eSIM – embedded - Subscriber Identity
Module
MDMS – Mobile Device Management System
Wi-Fi – Wireless Fidelity
ADSL - Asymmetric
Digital Subscriber Line
CCTV - Closed Circuit Television
CDMA - Code
Division Multiple Access
IPX/SPX - Internetwork Packet Exchange/ Sequenced
Packet Exchange
DTH - Direct To Home
GSM - Global System for Mobile
Communications
