BACHELOR OF COMMERCE FIFTH SEMESTER
Introduction to Computer Network
A computer network is a group of
devices connected with each other through a transmission medium such as wires,
cables etc. These devices can be computers, printers, scanners, Fax machines
etc.
The purpose of having computer
network is to send and receive data stored in other devices over the network.
These devices are often referred as nodes.
There are five basic
components of a computer network
Message:
It is the data or information which needs to be transferred from one device to
another device over a computer network.
Sender: Sender is the device that has the data and needs to send the data to
other device connected to the network.
Receiver: A receiver is the device which is expecting the data from other device
on the network.
Transmission
media: In order to transfer data from one device to another device
we need a transmission media such as wires, cables, radio waves etc.
Protocol: A protocol is a set of rules that are agreed by both sender and
receiver, without a protocol two devices can be connected to each other but
they cannot communicate. In order to establish a reliable communication or data
sharing between two different devices we need set of rules that are called
protocol.
For example http and https
are the two protocols used by web browsers to get and post the data to internet; similarly smtp protocol is used by email
services connected to the internet.
Evolution of Networking
Computers became able to exchange
data in automatic mode, which, essentially, is the basic mechanism of any
computer network. Developers of the first networks implemented services for
file exchange, database synchronization, e-mail and other network services.
ARPANET
ARPANET was established by the
Advanced Research Projects Agency (ARPA) in 1969 for two main reasons:
• To allow the transfer of data
between various institutes of research.
• To answer the call of the U.S.
Department of Defence for a technology to provide messaging capabilities to the
government in the event of nuclear war.
World Wide Web (WWW)
The World-Wide Web is a collection of
documents and services. It is distributed across the Internet and linked
together by hypertext links. The web is therefore a subset of the Internet.
World
Wide Web was created by Timothy Berners Lee in 1989
at CERN in Geneva.
Web page is a document available
on World Wide Web. A web page can contain 
information including text, graphics, audio,
video and hyper links. These hyper links are the link to other web pages.
Web
Browser is application software that allows us to view and explore
information on the web.
Following
are the most common web browser available today:
WWW Operation
WWW works on client- server approach.
Following steps explains how the web works:
1. User enters the URL (say
http://www. tngovernmentjobs.in/) of the web page in the address bar of web
browser.
2. Then browser requests the Domain
Name Server for the IP address corresponding to www.tngovernmentjobs.in.
3. After receiving IP address,
browser sends the request to web page and web server using HTTP protocol.
4. Then web server receives request
using HTTP protocol and checks for the requested web page. If found it returns
it back to the web browser and close the HTTP connection.
5. Now the web browser receives the
web page, it interprets and displays the contents of web page in web browser’s
window.
Web server is a computer where the
web content is stored. Basically web server is used to host the web sites.
Internet
• Internet is a world-wide global
system of interconnected computer networks.
• Internet uses the standard Internet
Protocol (TCP/IP).
• Every computer in internet is
identified by a unique IP address.
• IP Address is a unique set of
numbers (such as 110.22.33.114) which identifies a computer location.
• A special computer DNS (Domain Name
Server) is used to give name to the IP Address so that user can locate a
computer by a name.
• Internet is accessible to every
user all over the world.
Advantages
Ø Internet allows us to communicate
with the people sitting at remote locations. There are various apps available
on the web that uses Internet as a medium for communication.
One can find various social networking sites such as:
Facebook
Twitter
Yahoo
Google+
Flickr
Orkut
Ø One can surf for any kind of
information over the internet with the help of a search engine.
Ø Apart from communication and source
of information, internet also serves a medium for entertainment.
Following are the various modes for entertainment over internet.
Online Television
Online Games
Songs
Videos
Social Networking Apps
Internet Services
Ø Internet Banking
Ø Online Educational Services
Ø Online Shopping
Ø Online Ticket Booking
Ø Online Bill Payment
Ø Data Sharing
Ø E-mail
Internet provides concept of
electronic commerce, that allows the business deals to be conducted on
electronic systems
Data transmission
Data transmission is the process
of sending digital or analog data over a communication medium to one or more
computing, network, communication or electronic devices. It enables the
transfer and communication of devices in a point-to-point, point-to-multipoint
and multipoint-to-multipoint environment.
Data transmission is also known as digital
transmission or digital communications.
Data transmission can be analog and
digital but is mainly reserved for sending and receiving digital data. It works when a device or piece
of equipment, such as a computer, intends to send a data object or file to one
or multiple recipient devices, like a computer or server. The digital
data originates from the source device in the form of discrete signals or
digital bit streams. These data streams/signals are placed over a communication
medium, such as physical copper wires, wireless carriers and optical fiber, for
delivery to the destination/recipient device. Moreover, each outward signal can
be baseband or passband.
In addition to external
communication, data transmission also may be internally carried to a device.
For example, the random access memory
(RAM) or hard disk that sends data to a processor is also a form of data
transmission.
Difference between Analog Communication and Digital
Communication
1.
Analog Communication:
In analog communication the data is transferred with the help of analog signal
in between transmitter and receiver. Any type of data is transferred in analog
signal. Any data is converted into electric form first and after that it is
passed through communication channel. Analog communication uses a continuous
signal which varies in amplitude, phase, or some other property with time in
proportion to that of a variable.
The below figure illustrates
the Analog Communication System:
2.
Digital Communication:
In digital communication digital signal is used rather than analog signal for
communication in between the source and destination. The digital signal
consists of discrete values rather than continuous values. In digital
communication physical transfer of data occurs in the form of digital bit
stream i.e 0 or 1 over a point-to-point or
point-to-multipoint transmission medium. In digital communication the
digital transmission data can be broken into packets as discrete messages which
is not allowed in analog communication.
The below figure illustrates the Digital Communication
System:
Difference between Analog Communication and Digital
Communication:
|
Sl No |
ANALOG
COMMUNICATION |
DIGITAL
COMMUNICATION |
|
01. |
In analog
communication analog signal is used for information transmission. |
In digital
communication digital signal is used for information transmission. |
|
02. |
Analog communication uses analog
signal whose amplitude varies continuously with time from 0 to 100. |
Digital communication uses digital
signal whose amplitude is of two levels either Low i.e., 0 or either High
i.e., 1. |
|
03. |
It gets affected by
noise highly during transmission through communication channel. |
It gets affected by
noise less during transmission through communication channel. |
|
04. |
In analog communication only limited
number of channels can be broadcasted simultaneously. |
It can broadcast large number of
channels simultaneously. |
|
05. |
In analog
communication error Probability is high. |
In digital
communication error Probability is low. |
|
06. |
In analog communication noise immunity
is poor. |
In digital communication noise
immunity is good. |
|
07. |
In analog
communication coding is not possible. |
In digital
communication coding is possible. Different coding techniques can be used to
detect and correct errors. |
|
08. |
Separating out noise and signal in
analog communication is not possible. |
Separating out noise and signal in
digital communication is possible. |
|
09. |
Analog communication
system is having complex hardware and less flexible. |
Digital communication
system is having less complex hardware and more flexible. |
|
10. |
In analog communication for
multiplexing Frequency Division Multiplexing
(FDM) is used. |
In Digital communication for
multiplexing Time Division Multiplexing
(TDM) is used. |
|
11. |
Analog communication
system is low cost. |
Digital communication
system is high cost. |
|
12. |
It requires low bandwidth. |
It requires high bandwidth. |
|
13. |
Power consumption is
high. |
Power consumption is
low. |
|
14. |
It is less portable. |
Portability is high. |
|
15. |
No privacy or privacy
is low, so it is not highly secured. |
Privacy is high, so
it is highly secured. |
|
16. |
Not assures an accurate data
transmission. |
It assures a more accurate data
transmission. |
|
17. |
Synchronization
problem is hard. |
Synchronization
problem is easier. |
The transmission media is nothing but the physical media
over which communication takes place in computer networks.
Magnetic Media
One of the most convenient ways to
transfer data from one computer to another, even before the birth of
networking, was to save it on some storage media and transfer physical from one
station to another. Though it may seem old-fashion way in today’s world of high
speed internet, but when the size of data is huge, the magnetic media comes
into play.
For
example, a bank has to handle and transfer huge data of its customer, which stores a backup of it at some
geographically far-away place for security reasons and to keep it from
uncertain calamities. If the bank needs to store its huge backup data then its,
transfer through internet is not feasible. The WAN links may not support such
high speed. Even if they do; the cost too high to afford.
In these cases, data backup is stored
onto magnetic tapes or magnetic discs, and then shifted physically at remote
places.
Twisted Pair Cable
A twisted pair cable is made of two
plastic insulated copper wires twisted together to form a single media. Out of
these two wires, only one carries actual signal and another is used for ground
reference. The twists between wires are helpful in reducing noise
(electro-magnetic interference) and crosstalk.
There are two types of twisted pair cables:
Shielded
Twisted Pair (STP) Cable
Unshielded
Twisted Pair (UTP) Cable
STP cables comes with twisted wire
pair covered in metal
foil. This makes it more indifferent to noise and crosstalk.
UTP has seven categories, each
suitable for specific use. In computer networks, Cat-5, Cat-5e, and Cat-6
cables are mostly used. UTP cables are connected by RJ45 connectors.
Coaxial Cable
Coaxial cable has two wires of
copper. The core wire lies in the center and it is made of solid conductor. The
core is enclosed in an insulating sheath. The second wire is wrapped around
over the sheath and that too in turn encased by insulator sheath. This all is
covered by plastic cover.
Because of its structure, the coax
cable is capable of carrying high frequency signals than that of twisted pair
cable. The wrapped structure provides it a good shield against noise and cross
talk. Coaxial cables provide high bandwidth rates of up to 450 mbps.
There are three categories of coaxial
cables namely, RG-59 (Cable TV), RG-58 (Thin Ethernet), and RG-11 (Thick
Ethernet). RG stands for Radio Government.
Cables are connected using BNC
connector and BNC-T. BNC terminator is used to terminate the wire at the far
ends.
Power Lines
Power Line communication (PLC) is
Layer-1 (Physical Layer) technology which uses power cables to transmit data
signals. In PLC, modulated data is sent over the cables. The receiver on the
other end de-modulates and interprets the data.
Because power lines are widely
deployed, PLC can make all powered devices controlled and monitored. PLC works
in half-duplex.
There are two types of PLC:
Narrow
band PLC
Broad
band PLC
Narrow band PLC provides lower data
rates up to 100s of kbps, as they work at lower frequencies (3-5000 kHz).They
can be spread over several kilometers.
Broadband PLC provides higher data
rates up to 100s of Mbps and works at higher frequencies (1.8 – 250 MHz).They
cannot be as much extended as Narrowband PLC.
Fiber Optics
Fiber Optic works on the properties
of light. When light ray hits at critical angle it tends to refracts at 90
degree. This property has been used in fiber optic. The core of fiber optic
cable is made of high quality glass or plastic. From one end of it light is
emitted, it travels through it and at the other end light detector detects light
stream and converts it to electric data.
Fiber Optic provides the highest mode
of speed. It comes in two modes, one is single mode fiber and second is
multimode fiber. Single mode fiber can carry a single ray of light whereas
multimode is capable of carrying multiple beams of light.
Fiber Optic also comes in
unidirectional and bidirectional capabilities. To connect and access fiber
optic special type of connectors are used. These can be Subscriber Channel
(SC), Straight Tip (ST), or MT-RJ.
Classification of Networks (LAN, MAN, WAN)
|
Another important criterion for
classifying networks is their scale (physical size). As shown in Figure there
are: 1.
Personal Area Network (PAN) 2.
Local Area Network (LAN) 3.
Metropolitan Area Network (MAN) 4.
Wide Area Networks (WAN) Personal Area Network (PAN): The interconnection of devices within the range of an
individual person, typically within a range of 10 meters. For example, a
wireless network connecting a computer with its keyboard, mouse or printer is
a PAN. Also, a PDA that controls the user’s hearing aid or pacemaker fits in
this category. Another example of PAN is a Bluetooth. Typically, this kind of
network could also be interconnected without wires to the Internet or other
networks. Local Area Network (LAN): Privately-owned networks covering a small geographic
area, like a home, office, building or group of buildings (e.g. campus). They
are widely used to connect computers in company offices and factories to
share resources (e.g., printers) and exchange information. LANs are
restricted in size, which means that the worst-case transmission time is
bounded and known in advance. Knowing this bound makes it possible to use
certain kinds of designs that would not otherwise be possible. It also
simplifies network management. Traditional LANs run at speeds of 10 Mbps to
100 Mbps, have low delay (microseconds or nanoseconds), and make very few
errors. Newer LANs operate at up to 10 Gbps. Early LAN (Local Area Network)
networks were formed using coaxial cable, coax is an electric cable and it is
used to carry radio signals. LAN (Local Area Network) setup is
developed by connecting two or more than two computers with each other using
a physical connection in order to share files and data overtime. Metropolitan Area Network (MAN): Covers a larger geographical area than is a LAN,
ranging from several blocks of buildings to entire cities. MANs can also
depend on communications channels of moderate-to-high data rates. A MAN might
be owned and operated by a single organization, but it usually will be used
by many individuals and organizations. MANs might also be owned and operated
as public utilities. They will often provide means for internetworking of
LANs. Metropolitan Area Networks can span up to 50km, devices used are modem
and wire/cable. Most widely used technologies to
develop a MAN (Metropolitan Area Network) network are FDDI (fiber
distribution data interface), ATM (Asynchronous Transfer Mode) and
SMDS (switched multi megabit data service).ATM (Asynchronous Transfer Mode) is
the most frequently used of all. ATM (Asynchronous Transfer Mode) is a
digital data transfer technology. It was developed in 1980 to improve the
transportation of real time data over a single network. ATM (Asynchronous
Transfer Mode) works just like cell relay system, where data is separated in
the form of fixed equal sized packets and is transferred overtime. The
purpose of ATM (Asynchronous Transfer Mode) was to access clear audio and
video results during a video conferencing. Wide Area Networks (WAN): Computer network that covers
a large geographical area, often a country or continent. (Any network 1 whose
communications links cross metropolitan, regional, national boundaries). Less
formally, a network that uses routers and public communications links. Routers
will be discussed later. WAN (Wide Area
Network) networks are established often by seeking help from telecomm
departments who provide the] facility of leased lines. Router is connected to
the LAN at one side and a hub is attached at the other end. |
What is multiplexing?
Multiplexing, or muxing, is a
way of sending multiple signals or streams of information over a
communications link at the same time in the form of a single, complex signal.
When the signal reaches its destination, a process called demultiplexing,
or demuxing, recovers the separate signals and outputs them to individual
lines.
Multiplexing is a method used by
networks to consolidate multiple signals -- digital or analog -- into
a single composite signal that is transported over a common medium, such as a fiber
optic cable or radio wave. When the composite signal reaches its
destination, it is demultiplexed, and the individual signals are restored and
made available for processing.
Networks use a variety of
multiplexing techniques, but at a conceptual level, they all operate in a
similar manner. The individual network signals are input into a multiplexer
(mux) that combines them into a composite signal, which is then transmitted
through a shared medium. When the composite signal reaches its destination, a demultiplexer
(demux) splits the signal back into the original component signals and outputs
them into separate lines for use by other operations
What Does Concentrator Mean?
A concentrator aggregates and
forwards data packets within a system. A concentrator may also administrate
various dial-up internet calls and function as a network router. In general,
the term “concentrator” is used for either of these essential tasks.
Some IT professionals may use the
term “network concentrator” to talk about a system that takes in buffered
packets and puts them into a single queue. The concentrator may take packets
from FIFO buffers and put them in a position for linear handling.
IT professionals may talk about a
network concentrator as a “forwarder” or more generally point out this function
within a network system that handles multiple streams or threads and combines
them into a single point of service. Concentrators may also be part of
troubleshooting efforts, where system administrators may check to see that the
concentrator is taking in and outputting signals correctly.
Components of Computer Network
A computer network is a system of
interconnected computing devices used to share information and communicate
electronically among a wide variety of users. The devices may be connected with
a wire or may use a wireless method for transmitting the information.
Every setup requires some hardware
and software components for installing the networks. To run the network
systematically, there are certain components with different features and
abilities.
HARDWARE COMPONENTS
Hardware components are the ones that
are visible and can be touched; these are the components that are connected to
the network with or without a wire.
Some of the commonly used Hardware
components are-
1. Network
Interface Card
A network interface card is a
must-install hardware component in all the devices as it enables the devices to
be able to connect to the network. It is in the form of a circuit board with a
unique MAC address installed in the computer. It performs the function of
sending and receiving data and controlling the flow of data over the network.
It is capable of transferring data at the speed of 10,100 to 1000 Mb/s. It is
also called a LAN or Network Adapter.
2. Servers
Servers are supreme computers with
high-level configurations responsible for holding shared files, programs,
resources, and the network operating system. It is also called a Host Computer
because they provide access to the network resources to all the connected
users. Few examples are file servers, database servers, web servers.
3. Clients
Clients are computer device that
connects to and uses the network and shared network resources. They are
basically the users of the network. Many corporate organizations have client
computers for their employees associated with a corporate server.
4. Peers
Peers refer to the same devices over
the computer network that shares similar rights and functionality as another.
Two PCs can be peers, but a PC and a Server are not because they don't share similar
operations.
5. Transmission
Media
These can be defined as the link used
to transmit information among devices within the computer network. Transmission
Media can be of two types- Guided Medium, which uses cables and wires to share
data, for example, coaxial cable, power lines, or fibre optics. Secondly, a
Non-Guided Medium (also known as the wireless medium) uses electromagnetic
waves to transmit the data, such as radio transmission, infrared transmission,
or light transmission.
6. Connecting
Devices
Connecting devices act as the
middleware between networks and computers, some of the commonly used connecting
devices are-
Hubs- A hub is a central connection of all
the devices in a network system. It also connects all the computer devices. It
acts as a distribution point as it processes requests from the client computer
and provides the required information from the target device to the client
computer. Hubs nowadays are becoming obsolete because there are better
technologies available in the form of Switches and Routers.
Switches-It acts as a controller which
connects various devices like computers, printers, and other hardware devices
together. It also enables the free flow of information, sharing of resources,
and reducing the cost.
Routers- Routers are used to connect multiple
devices with an internet connection. It is an inexpensive method as it enables
sharing information and connecting multiple devices through one internet
connection.
SOFTWARE COMPONENTS
1. Network
Operating System
Network Operating Systems are
computer operating systems that facilitate the connection and communication of
all the computing devices connected over a network. It enables file sharing,
maintaining and creating a database, providing access to hardware such as
printers, plotters, or fax machines. The benefit of a Network Operating System
is that it facilitated stability, better security, and the capability of
managing data, users, groups, and other network functionalities. Some common
Network OS is Windows. Linus, Unix, etc.
2. Protocol
Suite
A protocol is a set of defined rules
guidelines to be followed by every other device connected to the network.
Protocol suites are a group of related protocols designed for computer
networks. Two Protocol Suites are- OSI Model (Open System Interconnections),
which decides how the data must flow between multiple computers and TCP/IP
(Transmission Protocol and Internet Protocol), which gives instructions on how
to connect and share information over devices within a network.
Other network components
1. ARP
ARP or Address Resolution Protocol is
a communication protocol used to find out the physical address (MAC address)
associated with a given network. It is used during the data transmission
because the IP address of the device alone isn't enough; the machine's physical
address is required, which is discovered using ARP.
2. RARP
RARP or Reverse Address Resolution
Protocol is used by the client, devices to get its Internet Protocol address
over a computer network.
Computer Network Components
Computer network components are
the major parts which are needed to install the software. Some
important network components
are NIC, switch, cable, hub, router, and modem.
Depending on the type of network that we need to install, some network
components can also be removed. For example, the wireless network does not
require a cable.
Following are the major components required to install a
network:
NIC
NIC stands for network interface
card.
NIC is a hardware component used to
connect a computer with another computer onto a network
It can support a transfer rate of
10,100 to 1000 Mb/s.
The MAC address or physical address
is encoded on the network card chip which is assigned by the IEEE to identify a
network card uniquely. The MAC address is stored in the PROM (Programmable
read-only memory).
There are two types of NIC:
Wired
NIC
Wireless
NIC
Wired
NIC: The Wired NIC
is present inside the motherboard. Cables and connectors are used with wired
NIC to transfer data.
Wireless
NIC: The wireless
NIC contains the antenna to obtain the connection over the wireless network.
For example, laptop computer contains
the wireless NIC.
Hub
A Hub is a hardware device that
divides the network connection among multiple devices. When computer requests
for some information from a network, it first sends the request to the Hub
through cable. Hub will broadcast this request to the entire network. All the
devices will check whether the request belongs to them or not. If not, the
request will be dropped.
The process used by the Hub consumes
more bandwidth and limits the amount of communication. Nowadays, the use of hub
is obsolete, and it is replaced by more advanced computer network components
such as Switches, Routers.
Switch
A switch is a hardware device that
connects multiple devices on a computer network. A Switch contains more
advanced features than Hub. The Switch contains the updated table that decides
where the data is transmitted or not. Switch delivers the message to the
correct destination based on the physical address present in the incoming
message. A Switch does not broadcast the message to the entire network like the
Hub. It determines the device to whom the message is to be transmitted.
Therefore, we can say that switch provides a direct connection between the
source and destination. It increases the speed of the network.
Router
A router is a hardware device which
is used to connect a LAN with an internet connection. It is used to receive,
analyze and forward the incoming packets to another network.
A router works in a Layer 3
(Network layer) of the OSI Reference model.
A router forwards the packet based on
the information available in the routing table.
It determines the best path from the
available paths for the transmission of the packet.
Advantages
of Router:
Security: The information which is
transmitted to the network will traverse the entire cable, but the only
specified device which has been addressed can read the data.
Reliability: If the server has stopped
functioning, the network goes down, but no other networks are affected that are
served by the router.
Performance: Router enhances the overall
performance of the network. Suppose there are 24 workstations in a network
generates a same amount of traffic. This increases the traffic load on the
network. Router splits the single network into two networks of 12 workstations
each, reduces the traffic load by half.
Modem
A modem is a hardware device that
allows the computer to connect to the internet over the existing telephone
line.
A modem is not integrated with the
motherboard rather than it is installed on the PCI slot found on the
motherboard.
It stands for Modulator/Demodulator.
It converts the digital data into an analog signal over the telephone lines.
Based on the differences in speed and transmission rate, a modem
can be classified in the following categories:
Ø Standard PC modem or Dial-up modem
Ø Cellular Modem
Ø Cable modem
Ø Cables and Connectors
Ø Cable is a transmission media used
for transmitting a signal.
There are three types of cables used in transmission:
Ø Twisted pair cable
Ø Coaxial cable
Ø Fibre-optic cable
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