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K.P.B . HINDUJA CO L L E GE
O F CO M M E RCE
S UB JE CT - CO M P UTE R
S YS TE M S & A P P L ICATIO NS
TO P IC – DATA
CO M M UNICATIO N,
NE TWO R KING & INTE R NE T
N A M E – K U S A I FATA K DAWA L A
CLASS – T.Y.B.COM
DIVISION - A
ROLL NO. - 17
SEMESTER – V
YEAR - 2013-2014

Data Communication:
There was a time when the term “data” referred exclusively to computer text information. Today,
the definition of data has expanded to include any piece of communication that can be expressed
in the bits and bytes of the digital world. This can range from text to graphics; from voice to
music; and from simple emails to complex web content. The rapid growth of the Internet has
enhanced the role of data communications in modern life. Computer networks are the cables and
floodgates for this ocean of information, which is now being used to encourage technologies,
such as mobile computing, wireless communication, high-speed broadband, instant messaging
and other innovations. An entire generation of hardware – including hubs, bridges, switches and
routers was developed to support this modernization. At the same time, protocols and standards
are being developed and refined so that these new information appliances share a common
language in order to work effectively together. We all are familiar with some sorts of
communication in our day to day life. For communication of information and messages we use
telephone and postal communication systems. Similarly data and information from one computer
system can be transmitted to other systems across geographical areas. Thus data transmission is
the movement of information using some standard methods. These methods include electrical
signals carried along a conductor, optical signals along an optical fibers and electromagnetic
areas. Suppose a manager has to write several letters to various clients. First he has to use his PC
and Word Processing package to prepare the letter, if the PC is connected to all the client’s PC
through networking, he can send letters to all the clients within minutes. Thus irrespective of
geographical areas, if PC’s are connected through communication channel, the data and
information, computer files and any other programs can be transmitted to other computer
systems within seconds. The modern form of communication like e-mail and internet is possible
only because of computer networking.
The key technology of the information age is computer communications. The value of
high-speed data communication network is that it brings the message sender and receiver closer
together in time. Data communication and networking is truly global area of study. It facilitates
more efficient use of computers and improves the day to day control of business by providing
faster information flow. The information society where the information and intelligence are the
key drivers of personal, business, and national success has arrived. Data communication is the
principle enabler of the rapid information exchange and will become more important than the use
of computers themselves in the future.
Hence, to be more familiar that what is data communication and its capabilities along
with its limitation, one has to be familiar with its components.
Components – Data communication has five basic components: the message, the sender, the
receiver, the medium and the protocol.
1. Message: In a data communication system, the message is the information sent out through the
system. The message may include numbers, words, photos, other graphics, sounds, video or a
combination of any of these. Messages in a data communication system are put together in

analog or digital form or broken into groups or segments of data called packets. Each packet has
a payload--the actual data being sent--and a header—information about the type of data in the
payload, where it came from, where it is going, and how it should be reassembled so the message
is clear and in order when it arrives at the destination.
2. Sender: The sender in a data communication
sequence is the device that generates the messages.
Sometimes these devices are called sources or
transmitters instead of senders. Some sending
devices are desktop and laptop computers,
netbooks, smartphones, video cameras,
workstations, telephones, fax machines and tablets.
Television stations, radio stations, short wave
radios, and walkie talkies are also considered
senders in a data communication system.
3. Receiver: The receiver is the device on the other end of the data communication transmission
that gets the message. Many of the same devices that function as receivers also function as
senders, such as computers, smartphones and telephone handsets. Some, however, are only
receivers, such as radios, printers, or televisions.
4. Medium: The medium is the means by which the message travels from the sender to the
receiver. If the receiver and transmitter are within a building, a wire connects them. If they are
located at different locations, they may be connected by satellite, fiber optics or microwaves.
5. Protocol: A protocol is a set of rules that guides how data communication is carried out. Every
device that wants to communicate with each other must use the same protocol in order to
exchange messages.
Distributed Processing:
Distributed Processing, also known as distributed computing, is defined as using a network of
computers to perform specific tasks with one main computer used for more complicated tasks. It
is a phrase used to refer to a variety of computer systems that use more than one processor to run
an application. This includes parallel processing in which a single computer uses more than one
processor to execute programs. A distributed computer system consists of multiple software
components that are on multiple computers, but run as a single system. The computers that are in
a distributed system can be physically close together and connected by a local network, or they
can be geographically distant and connected by a wide area network. A distributed system can
consist of any number of possible configurations, such as mainframes, personal computers,
workstations, minicomputers, and so on. The goal of distributed computing is to make such a
network work as a single computer.

Networking:
Computer networks are used for data communications. A computer network can be defined as a
collection of nodes. A node can be any device capable of transmitting or receiving data. The
communicating nodes have to be connected by communication links. A computer network is
interconnection of various computer systems located at different places. In computer network
two or more computers are linked together with a medium and data communication devices for
the purpose of communication data and sharing resources. The computer that provides resources
to other computers on a network is known as server. In the network the individual computers,
which access shared network resources, are known as nodes. A node can be a computer, printer,
or any other device capable of sending and/or receiving data generated by other nodes on the
network.
Types of Networks - Networks are categorized on the basis of their size. The 3 basic categories
of computer networks are:
1. Local Area Network (LAN) - A LAN is a local area
network that is a small collection of computers in a small
geographical area of less than couple of kilometers and is very
fast in data transfer. Depending on technology
implementation a LAN can be as simple as two PC’s and a
printer got connected in a small office or it can extend
through out an organization and include multimedia like text,
video etc. in data transfers. LAN is usually limited to a few
kilometers of area. It may be privately owned and could be a
network inside an office on one of the floor of a building or a
LAN could be a network consisting of the computers in the
entire building.
2. Metropolitan Area Network (MAN) - The metropolitan area network is designed to cover an
entire city. It can be a single network such as cable
TV or a number of LANs connected together within a
city to form a MAN. Privately laid cables or public
leased lines may be used to form such network. It is a
network with a size between a LAN and a WAN. It
normally covers the area inside a town or a city. It is
designed for customers who need a high-speed
connectivity, normally to the Internet, and have
endpoints spread over a city or part of city. A good example of a MAN is the part of the
telephone company network that can provide a high-speed DSL line to the customer.

3. Wide Area Network (WAN) – WAN provides
long-distance transmission of data, image, audio,
and video information over large geographic areas
that may comprise a country, a continent, or even
the whole world. A WAN is a data
communications network that covers a relatively
broad geographic area, often a country or
continent. It contains a collection of machines
intended for running user programs. These
machines are called hosts. The hosts are connected
by subnet. The purpose of subnet is to carry messages from hosts to hosts. The subnet includes
transmission facilities, switching elements and routers provided by common agencies, such as
telephone companies. Nowadays routers with satellite links are also becoming part of the WAN
subnet. All these machines provide long distance transmission of data, voice, image and video
information. Unlike LAN which depend on their own hardware for transmission, WANs may
utilize public, leased, or private communication devices when it come across and therefore span
an unlimited number of kilometers. A network device called a router connects LANs to a WAN.
The Internet is the largest WAN in existence.
Network Structures - The term architecture/structure can refer to either hardware or software,
or a combination of hardware and software. The architecture of a system always defines its broad
outlines, and may define precise mechanisms as well. An open architecture allows the system to
be connected easily to devices and programs made by other manufacturers. Open architectures
use off-the-shelf components and conform to approved standards. A system with a closed
architecture, on the other hand, is one whose design is proprietary, making it difficult to connect
the system to other systems. As we have seen before, network architectures can be broadly
classified as using either peer-to-peer or client/server architecture.
1. Peer-to-Peer Architecture: This is a type of network in which each workstation has equivalent
capabilities and responsibilities. This differs from client/server architecture, in which some
workstations are dedicated to serving the others. Peer-to-peer networks are generally simpler and
less expensive, but they usually do not offer the same performance under heavy loads.
2. Client/Server Architecture: Client/server describes the relationship between two computer
programs in which one program, the client, makes a service request from another program, the
server, which fulfills the request. Although the client/server idea can be used by programs within
a single computer, it is a more important idea in a network. In a network, the client/server model
provides a convenient way to interconnect programs that are distributed efficiently across
different locations. Computer transactions using the client/server model are very common. The
client/server model has become one of the central ideas of network computing. Most business
applications being written today use the client/server model.

Network Topologies - Topology refers to the shape of a network, or the network's layout. How
different nodes in a network are connected to each other and how they communicate is
determined by the network's topology. Topologies are either physical or logical. Below are the
most common network topologies.
1. Bus Topology: A bus network is an
arrangement in a local area network (LAN) in
which each node (workstation or other device) is
connected to a main cable or link called the bus.
The illustration shows a simple computer setup
on a network using the bus topology. In a bus
topology all devices are connected to the
transmission medium as backbone. There must be
a terminator at each end of the bus to avoid signal
reflections, which may distort the original signal.
Signal is sent in both directions, but some buses are one directional. Good for small networks.
The main problem with the bus topology is failure of the medium will seriously affect the whole
network. Any small break in the media the signal will reflect back and cause errors. The whole
network must be shutdown and repaired. In such situations it is difficult to troubleshoot and
locate where the break in the cable is or which machine is causing the fault; when one device
fails the rest of the LAN fails.
2. Star Topology: In a star topology each station is
connected to a central node. The central node can be either a
hub or a switch. The star topology does not have the
problem as seen in bus topology. The failure of a media
does not affect the entire network. Other stations can
continue to operate until the damaged segment is repaired.
The advantages are cabling is inexpensive, easy to wire,
more reliable and easier to
manage because of the use of
hubs which allow defective cable
segments to be routed around; network growth is easier. The
disadvantages are all nodes receive the same signal therefore dividing
bandwidth. This topology is the dominant physical topology today.
3. Ring Topology: Ring topology is one of the old ways of building
computer network design and it is pretty much obsolete. FDDI, SONET or Token Ring
technologies are used to build ring technology. It is not widely popular in terms of usability but
incase if one finds it anywhere it will mostly be in schools or office buildings. Such physical
setting sets up nodes in a circular manner where the data could travel in one direction where each
device on the right serves as a repeater to strengthen the signal as it moves ahead.

Transmission Media - A transmission medium can be broadly defined as anything that can
carry information from a source to a destination. In telecommunications, transmission media can
be divided into two broad categories: guided (wired) and unguided (unwired). Guided media
include twisted-pair cable and coaxial cable. Unguided medium is wireless.
A. Guided Media - Guided Transmission media uses a cabling system that guides the data signals
along a specific path.
1. Twisted-pair cable: The wires are twisted together in pairs. A twisted pair consists of two
conductors (normally copper), each with its own plastic insulation, twisted together. One of the
wires is used to carry signals to the receiver, and the other is used only as a ground reference.
The receiver uses the difference between the two. Twisted pair cables are most effectively used
in a system that uses a balanced line method of transmission.
2. Co-Axial Cable: Coaxial cable consists of 2 conductors. Coaxial cable is groups of specially
wrapped and insulated wires that are able to transfer data at higher rate. They consist of a central
copper wire surrounded by an insulation over which copper mesh is placed. They are used for
long distance telephone lines and local area network for their noise immunity and faster data
transfer.
B. Unguided Media - Unguided media transport data without using a physical conductor. This
type of communication is often referred to as wireless communication.
1. Radio waves: Electromagnetic wave ranging in frequencies between 3 KHz and 1GHz are
normally called radio waves. Radio waves particularly those waves that propagate in sky mode,
can travel long distances. This makes radio waves a good candidate for long-distance
broadcasting such as AM radio.
2. Microwaves: Electromagnetic waves having frequencies between 1 and 300 GHz are called
microwaves. The transmitter and receiver of a microwave system should be in line-of-sight
because the radio signal cannot bend. With microwave very long distance transmission is not
possible.
3. Infrared: Infrared waves, with frequencies from 300 GHz to 400 THz (wavelengths from 1
mm to 770 nm), can be used for short-range communication. Infrared waves, having high
frequencies, cannot penetrate walls.
Network Models: 1. TCP/IP MODEL - The Internet Protocol Suite, TCP/IP, is a suite of
protocols used for communication over the internet. From lowest to highest, the layers are:
Layer 1. Network Access Layer: Network Access Layer is the first layer of the four layer TCP/IP
model. Network Access layer defines details of how data is physically sent through the network,
including how bits are electrically or optically signaled by hardware devices that interface
directly with a network medium, such as coaxial cable, optical fiber, or twisted pair copper wire.
Layer 2. Internet Layer: The routing and delivery of data is the responsibility of this layer and is

the key component of this architecture. The Internet layer is also responsible for routing of IP
data grams.
Layer 3. Transport Layer: This layer acts as the delivery service used by the application layer.
The two protocols used are TCP and UDP. Transport layer defines the level of service and status
of the connection used when transporting data.
Layer 4. Application Layer: Application layer is the top most layer of four layer TCP/IP model.
Application layer is present on the top of the Transport layer. Application layer defines TCP/IP
application protocols and how host programs interface with transport layer services to use the
network. Note that the Network Access Layer combines the functions of Data link Layer and
Physical Layer.
2. The Open Systems Interconnection (OSI) Model - The Open Systems Interconnection (OSI)
Model was developed by International Organization for Standardization (ISO). ISO is the
organization, OSI is the model. The purpose of the OSI model is to show how to facilitate
communication between different systems without requiring changes to the logic of the
underlying hardware and software. It defines the protocols for network communications.
Physical (Layer 1): This layer conveys the bit stream - electrical impulse, light or radio signal --
through the network at the electrical and mechanical level. It provides the hardware means of
sending and receiving data on a carrier, including defining cables, cards and physical aspects.
Data Link (Layer 2): The data link layer provides error-free transfer of data frames from one
node to another over the physical layer, allowing layers above it to assume virtually error-free
transmission over the link.
Network (Layer 3): This layer provides switching and routing technologies, creating logical
paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding
are functions of this layer, as well as addressing, internetworking, error handling, congestion
control and packet sequencing.
Transport (Layer 4): This layer provides transparent transfer of data between end systems, or
hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data
transfer.
Session (Layer 5): This layer establishes, manages and terminates connections between
applications. The session layer sets up, coordinates, and terminates conversations, exchanges,
and dialogues between the applications at each end. It deals with session and connection
coordination.
Presentation (Layer 6): The presentation layer formats the data to be presented to the application
layer. It provides the functions of translation, encryption and compression.
Application (Layer 7): The application level provides the users access to network resources. The
application layer takes care of the incompatibilities and allows a smooth transfer between
systems.

Internet:
The internet in simple terms is a network of the interlinked computer networking worldwide,
which is accessible to the general public. These interconnected computers work by transmitting
data through a special type of packet switching which is known as the IP or the internet protocol.
Internet is such a huge network of several different interlinked networks relating to the business,
government, academic, and even smaller domestic networks, therefore internet is known as the
network of all the other networks. These networks enable the internet to be used for various
important functions which include the several means of communications like the file transfer, the
online chat and even the sharing of the documents and web sites on the WWW, or the World
Wide Web. The features of internet are vast and endless but some of them are as follows –
1. E-Mail: E-mail stands for electronic mail. This is one of the most widely used features of
Internet. Mails are regularly used today where without the help of postage stamp we can transfer
mails anywhere in the world. With electronic mail the service is similar. But here data is
transmitted through Internet and therefore within minutes the message reaches the destination
may it be anywhere in the world. Therefore the mailing system through e-mail is excessively fast
and is being used widely for mail transfer.
2. Blogs: A blog is a website in which items are posted on a regular basis and displayed in
reverse chronological order. The term blog is a shortened form of weblog or web log. Authoring
a blog, maintaining a blog or adding an article to an existing blog is called “blogging”. Individual
articles on a blog are called “blog posts,” “posts” or “entries”. A person who posts these entries
is called a “blogger”. A blog comprises text, hypertext, images, and links (to other web pages
and to video, audio and other files). Blogs use a conversational style of documentation. Often
blogs focus on a particular “area of interest”, such as India’s fight against corruption. Some blogs
discuss personal experiences.’
3. IP Address: An IP address is a fascinating product of modern computer technology designed
to allow one computer (or other digital device) to communicate with another via the Internet. IP
addresses allow the location of literally billions of digital devices that are connected to the
Internet to be pinpointed and differentiated from other devices. In the same sense that someone
needs your mailing address to send you a letter, a remote computer needs your IP address to
communicate with your computer. "IP" stands for Internet Protocol, so an IP address is an
Internet Protocol address. An Internet Protocol is a set of rules that govern Internet activity and
facilitate completion of a variety of actions on the World Wide Web. Therefore an Internet
Protocol address is part of the systematically laid out interconnected grid that governs online
communication by identifying both initiating devices and various Internet destinations, thereby
making two-way communication possible. An IP address consists of four numbers, each of the
four numbers can range from 0 to 255. Here's an example of what an IP address might look like:
78.125.0.209. Without this numeric protocol, sending and receiving data over the World Wide
Web would be impossible.

4. Domain Name: Domain names function on the Internet in a manner similar to a physical
address in the physical world. Each part of the domain name provides specific information.
These pieces of information enable web browsers to locate the web page. The naming system is
closely regulated in order to prevent confusion or duplicate addresses. A domain name is a way
to identify and locate computers and resources connected to the Internet. No two organizations
can have the same domain name.
5. URL: URL stands for Uniform Resource Locator and is also sometimes written as URI (for
Uniform Resource Identifier). A URL is a formatted text string used by Web browsers, email
clients and other software to identify a network resource on the Internet. Network resources are
files that can be plain Web pages, other text documents, graphics, or programs. An example of a
URL is http://www.microsoft.com, which is the URL for the Microsoft’s official website.
6. Search Engine: A search engine makes it possible to find a specific bit of information amongst
the huge mass of data stored on the web. It is a Tool for finding information, especially on the
Internet or World Wide Web. Search engines are essentially massive databases that cover wide
areas of the Internet. Most consist of three parts: at least one program, called a spider, crawler, or
robot, which “crawls” through the Internet gathering information; a database, which stores the
gathered information; and a search tool, with which users search through the database by typing
in keywords describing the information desired (usually at a Web site dedicated to the search
engine). Essentially, a search engine is a computer program. The biggest ones, such as Google,
Microsoft's Bing, Yahoo!, and Ask, use giant clusters of computers to search the web.
7. Meta Search Engine: A meta search engine is a type of search engine that gives results based
on a combination of results from other search engine databases. It specializes in connecting
databases from a variety of search engines and linking search results to relevant sources. A meta
search engine is a search engine that queries many different search engines and combines the
results from all of them, or else displays the results separately but in one place. It does not
actually crawl the web itself, like a real search engine, instead relying on data gathered by others.
The meta search engine has been around almost as long as search engines themselves, and some
people find them preferable to using a single one, as they allow for a wider range of results. One
of the most popular meta engines in the past was DogPile, which won the Best Meta Search
Engine award in 2003.
Conclusion:
In conclusion, Today's society is in the middle of a technological boom. People can either choose
to take advantage of this era, or simply let it pass them by. Data Communication, Networking
and Internet are a boon to mankind and will forever stay as one of the best inventions of all time.

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