Data Communication and Network

Course: MBA-ISubject: IT For Manager

Unit-4

1

What is data Communication?

• Exchange of digital information between two digital devices is data communication.

• Data Communications is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it.

• The actual generation of the information is not part of Data Communications nor is the resulting action of the information at the receiver. Data Communication is interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process.

Types Of Data Communication

• Simplex• Half Duplex• Full Duplex• Serial

Simplex

• A simplex communication system sends a message in only one direction. The message source works as the transmitter.

• It sends the message over the data channel to the receiver. The receiver is the destination of the message.

• Examples of simplex data communication include radio stations and TV broadcasts. With the simplex channel, there is no ability by the receiver to respond to the message.

• For example, a radio station plays a song on your car radio. The data transferred is the song. You do not have the opportunity to send a message back via your car radio to the station.

half-duplex

• A data communication system provides messages in both directions but only allows transfer in one direction at a time.

• Once a party begins sending a transmission, the receiver must wait until the signal stops before responding.

• If the two data transfers attempt to send at the same time, they both fail.

• For instance, if you talk on a CB radio, you press a button and speak. If the receiver attempts to press the button and speak at the same time, neither one of you hear either message. The system is not capable of sending both ways simultaneously.

full duplex

• A full duplex is a communication that works both ways at the same time.

• Essentially, full duplex data communication is a set of two simplex channels, one works as a forward channel and the other as a reserve channel. The two channels link together at some point.

• An example of a full duplex communication system is a landline telephone. When talking on a telephone, both parties have the ability to speak at the same time. The data, carried both ways through the telephone line, runs simultaneously.

Serial communication

• Serial communication takes a data communication, breaks it up into small pieces, and sends the message one bit at a time through a channel.

• The receiver collects the small bits and reassembles them to compose the original message.

• Serial communication is the most common type of communication between electronic devices. \

• One example of serial communication in action is the data sent from a modem to the service provider.

Communication Media

• Magnetic Media• Twisted Pair Cable• Coaxial Cable• Power Lines• Fiber Optics

Magnetic Media

• One of the most convenient way to transfer data from one computer to another,

• For an example, say a Bank has Gigs of bytes of their customers’ data which stores a backup copy of it at some geographically far place for security and uncertain reasons like war or tsunami. If the Bank needs to store its copy of data which is Hundreds of GBs, transfer through Internet is not feasible way. Even WAN links may not support such high speed or if they do cost will be too high to afford.

• In these kinds of 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 is helpful in reducing noise (electro-magnetic interference) and crosstalk.

• It has two type• 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 cables has two wires of copper. The core wire lies in center and is made of

solid conductor. Core is enclosed in an insulating sheath. Over the sheath the second wire is wrapped around and that too in turn encased by insulator sheath. This all is covered by plastic cover.

• Because of its structure coaxial cables are capable of carrying high frequency signals than that of twisted pair cables. 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 Coax cables namely, RG-59 (Cable TV), RG-58 (Thin Ethernet) and RG-11 (Thick Ethernet. RG stands for Radio Government.

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 form.

• Fiber Optic provides the highest mode of speed.

• It comes in two modes, – single mode fiber and – second is multimode fiber..

Network Topology

Definition of Network Topology

Types of Network Topology

Differentiation Between theTypes of Network Topology

CONTENT

What is a Topology ?

The physical topology of a network refers to the configuration of cables,

computers and other peripherals.

DEFINITION

Bus network.

Ring network.

Star network.

TYPES OF NETWORK TOPOLOGY

All computers and devices connected to central cable or bus.

Consists of a main run of cable with a terminator at each end.

Popular on LANs because they are inexpensive and easy to install.

BUS TOPOLOGY

BUS TOPOLOGY

Cable forms closed ring or loop, with all computers and devices arranged along ring.

Data travels from device to device around entire ring, in one direction.

Primarily is used for LANs, but also is used in WANs.

RING TOPOLOGY

RING TOPOLOGY

All devices connect to acentral device, calledhub.

All data transferredfrom one computer toanother passes through hub.

STAR TOPOLOGY

STAR TOPOLOGY

ADVANTAGE DISADVANTAGE

1) Easy to connect computer or peripheral to a linear bus.

1) Entire network shuts down if there is a break in the main cable.

2) Requires less cable length than a star topology.

2) Terminators are required at both ends of the backbone cable.

3) Difficult to identify the problem if the entire network shuts down.

BUS

DIFFERENTIATION BETWEEN THE THREE TYPES OF NETWORK TOPOLOGY

ADVANTAGE DISADVANTAGE

1) Data is quickly transferred. 1) Data packets must pass through every computer

between the sender and recipient therefore, this makes it slower.

2) The transmission of data is relatively simple as packets travel in one direction only.

2) If any of the nodes fail then the ring is broken and data cannot be

transmitted successfully. 3) It is difficult to troubleshoot the ring.

RING

DIFFERENTIATION BETWEEN THE THREE TYPES OF NETWORK TOPOLOGY

ADVANTAGE DISADVANTAGE

1) Easy to install and wire. 1) Requires more cable length

than a linear topology.

2) Security can be implemented in the hub/switch.

2) If the hub or concentrator fails, nodes attached are disabled.

3) Easy to detect faults and to remove parts.

3) More expensive than linear bus topologies because of the

cost of the concentrators.

STAR

DIFFERENTIATION BETWEEN THE THREE TYPES OF NETWORK TOPOLOGY

DEFINITION• All computers

and devices connected to central cable

DEFINITION• All computers

and devices connected to central cable

BUS TOPOLOGY

ADVANTAGE• Easy to connect a

computer or peripheral to a linear

bus.

ADVANTAGE• Easy to connect a

computer or peripheral to a linear

bus.

• Requires less cable length than

a star topology.

• Requires less cable length than

a star topology.

DISADVANTAGE

• Entire network shuts down if

there is a break in the main cable.

DISADVANTAGE

• Entire network shuts down if

there is a break in the main cable.

• Terminators are required at both

ends of the backbone cable.

• Terminators are required at both

ends of the backbone cable.

• Difficult to identify the problem

if the entire network shuts down.

• Difficult to identify the problem

if the entire network shuts down.

SUMMARY

RING TOPOLOGY

DEFINITION• Cable forms

closed ring or loop, with all

computers and devices arranged

along ring.

DEFINITION• Cable forms

closed ring or loop, with all

computers and devices arranged

along ring.

ADVANTAGE• Data is quickly

transferred without a ‘bottle neck’.

ADVANTAGE• Data is quickly

transferred without a ‘bottle neck’.

• The transmission of data is relatively

simple as packets travel in one direction only.

• The transmission of data is relatively

simple as packets travel in one direction only.

DISADVANTAGE

• Data packets must pass through every computer between the sender and recipient therefore, this

makes it slower.

DISADVANTAGE

• Data packets must pass through every computer between the sender and recipient therefore, this

makes it slower.

• If any of the nodes fail then the ring is broken

and data cannot be transmitted successfully.

• If any of the nodes fail then the ring is broken

and data cannot be transmitted successfully.

• It is difficult to troubleshoot the ring.

• It is difficult to troubleshoot the ring.

SUMMARY

DEFINITION• All devices

connect to a central device,

called hub.

DEFINITION• All devices

connect to a central device,

called hub.

ADVANTAGE• Easy to install and

wire.

ADVANTAGE• Easy to install and

wire.

• Security can be implemented

in the hub/switch.

• Security can be implemented

in the hub/switch.

DISADVANTAGE• Requires more cable

length than a linear topology.

DISADVANTAGE• Requires more cable

length than a linear topology.

If the hub or concentrator fails,

nodes attached are disabled.

If the hub or concentrator fails,

nodes attached are disabled.

More expensive than linear bus topologies

because of the cost of the concentrators.

More expensive than linear bus topologies

because of the cost of the concentrators.

STAR TOPOLOGY

• Easy to detect faults and to

remove parts

• Easy to detect faults and to

remove parts

SUMMARY

Internet, Intranet and Extranets

What is Internet ?

• It is a Global network of computers, (servers or clients)to exchange information.

• It is a "network of networks" that includes millions of private and public, academic, business, and government networks (local or Global),linked by copper wires, wireless connections, and other technologies.

Hardware and Software of Internet

Variety of hardware and software are used to make Internet functional.

• Modem

Device that enables computers to communicate through phone lines.

When we start internet the our modem communicates to modem of ISP.

Continued…• Computer

In addition to a modem, you need a client capable of handling multiple data types.

• Software

Two types of software’s required to enable your PC as an Internet PC.

• Communication software to establish connection• Client software for browsing, e-mail, news.

these software’s are provided with windows itself.

Applications Of Internet

• Download programs and files• E-Mail• Voice and Video Conferencing• E-Commerce• File Sharing• Information browsing• Search the web addresses for access through search engine • Chatting and many more…

Disadvantages of Internet

• Theft of personal information such as name, address, credit card number etc.

• Virus threats nothing but a program which disrupts the normal functioning of your system.

• Spamming refers to receiving unwanted e-mails in bulk, which provide no purpose and needlessly obstruct the entire system.

• Pornography This is perhaps the biggest threat related to children’s healthy mental life. A very serious issue concerning the Internet.

Though, internet can also create havoc, destruction and its misuse can be very fatal, the advantages of it outweigh its disadvantages.

What is Intranet ?

• Internal company network that uses Internet standards (HTML, HTTP & TCP/IP protocols) & software.

• Accessed only by authorized persons, especially members or employees of the organization

Intranet Security

Two levels of Security required:

• Internal

It can be imposed by Public Key Security & Encryption Key.

• External

Through Firewall.

What is Firewall ?

• Security device located between firm’s internal network (intranet) & external network (internet).

• Regulates access into & out of a company’s network based on a set of rules.

Note : needs to be upgraded from time to time to check latest potential security problems.

Applications of Intranet

• Sharing of company policies/rules & regulations• Access employee database• Distribution of circulars/Office Orders• Access product & customer data• Sharing of information of common interest• Launching of personal/departmental home pages• Submission of reports • Corporate telephone directories

Disadvantages

Information overload lowers productivity True purpose of the Intranet is unknown to many

employees/departments Hidden or unknown complexity and costs

Productivityproblem

Unauthorized access Abuse of access Denial of service

Securityproblem

A company may not have person to update their

Fear of sharing information and the loss of control Limited bandwidth for the business

Managementproblem Intranet on a routine basis

What is Extranet ?

• Extranet is an Intranet for outside authorized users using same internet technology.

• Inter-organizational information system.

• enable outsiders to work together with company’s employees.

• open to selected suppliers, customers & other business partners

Examples..

• Dealers/distributors have access to product files such as :-

1. product specification,

2. pictures,

3. images, etc.

to answer the queries of the customer.

Components of extranets ..

Some basic infrastructure components such as the internet Including :-

• TCP/IP protocols,• E-mail,• Web-browsers,• External business partners &• Tele-commuting employees place order, check

status & send E-mail.

Benefits of Extranet

• Improved quality.• lower travel costs.• lower administrative & other overhead costs.• reduction in paperwork.• delivery of accurate information on time.• improved customer service.• better communication.• overall improvement in business

effectiveness.

Disadvantages

• The suppliers & customer who don’t have technical knowledge feel problem.

• Faceless contact.• Information can be misused by other competitors.• Fraud may be possible.• Technical Employees are required.

Clients, partners, customers

Layered System View

Intranet

Extranet

Internet

Corporate members

Global society: competitors

TAGS IN HTML

HTML

HTML – Hyper Text Markup Language

HTML documents describe web pages (Static Web Page)

HTML tags are keywords surrounded by angle brackets like

<html>

HTML tags normally come in pairs like <b> and </b>

The first tag in a pair is the start tag (opening tags), the

second tag is the end tag(closing tags)

IMPLEMENTATIONWHERE WE WRITE CODE :

1.Text Editor

1.Wordpad (In Windows OS)

2.Gedit Text Editor (Ubundu in LINUX)

3.NotePad

2.FrontPage or Dreamweaver

WHERE WE EXECUTE :

1.Double Click that HTML File. (or)

2.Right click – Open With Internet Explorer

Simple Code - 1

First Planet

First Planet

<html> .... </html> describes the web page

<body> ..... </body> is the visible page content

<html>

<body>

<h1>First Planet</h1>

<h6>First Planet</h6>

</body>

</html>

O/P :

Link TagHtml Links :

Html links are defined with the <a> tag

Syntax : <a href="http://www.gmil.com">Gmail</a>

Example : <html><body>

<a href="http://www.gmail.com">Gmail</a>

</body></html>

GmailO/P :If we click this link it goes to gmail

account

Image Tag

HTML Images :

HTML images are defined with the <img> tag.

Syntax : <img src "123.jpg" width="104" height="142" />

Example :<html><body>

<img src="word.jpg" width="104" height="142" />

</body></html>

O/P:

HTML RULESHTML Rules (Lines) :

The <hr /> tag is used to create an horizontal rule

(line).

Example:<html><body>

<h3>Exnora</h3>

<hr />

<h3>Safety Exnora</h3>

</body></html>

O/P :Exnora

Safety Exnora

HTML COMMENTSHTML Comments :

Comments can be inserted in the HTML code to

make it more readable and understandable. Comments are ignored by

the browser and are not displayed.

Syntax : <!-- some text →

Example :<html><body>

<!--It will not be displayed-->

<h3>Plant Trees </h3>

</body></html>

Plant Trees

O/P :

HTML TEXT FORMATTING

<html><body>

<b>Confidence</b><br />

<big>Hardwork</big><br />

<i>Preseverance</i><br />

<code>Samsung CRT</code><br />

This is_subscript<br />

This is^superscript

</body></html>

Some Formatting Tags are 1,b-Bold, 2.i-Italic, 3.code-Computer

code,4.sub-Subscript & 5.sup-Superscript

Implement it as a Exercise

(Practical)

HTML STYLE ATTRIBUTES

Tags Description

<center> Defines centered content

<font> Defines HTML fonts

<s> and <strike> Defines strikeout text

<u> Defines underlined text

Attributes Description

Align Defines the alignment of text

Bgcolor Defines the background color

Color Defines the text color

STYLE EXAMPLE<html>

<h1 style="text-align:center">NATURE</h1>

<body style="background-color:yellow">

<p style="font-family:Purisa;color:red">Plant Tree</p>

<p style="font-family:times;color:red">Save Our Generation</p>

<p style="font-size:40">Value Our Environment</p></body> </html>

NATUREPlant Tree

Save Our Generation

Value Our Environment

O/P :

HTML TABLES Tables are defined with the <table> tag.

A table is divided into rows (with the <tr> tag),

Each row is divided into data cells (with the <td> tag). The letters td stands for "table data," which is the content of a data cell.

Headings in a table are defined with the <th> tag.

<table border="1">

<tr> <td>row 1, cell 1</td>

<td>row 1, cell 2</td> </tr>

<tr> <td>row 2, cell 1</td>

<td>row 2, cell 2</td></tr>

</table>

row1,cell1 row1,cell2

row2,cell1 row2,cell2

TABLE FEATURES1.Table with a caption :

<caption>My Caption</caption>

2.Table cells that span more than one row/column :

<th colspan="2">Telephone</th>

<th rowspan="2">Telephone:</th>

3.Cell padding :

<table border="1" cellpadding="10">

4.Cell spacing :

<table border="1" cellspacing="10">

5.Add a background color or a background image to a table :

<table border="1" bgcolor="red">

HTML LISTS HTML supports ordered, unordered and definition lists.

Ordered Lists :

An ordered list is also a list of items. The list items are marked with numbers.

An ordered list starts with the <ol> tag. Each list item starts with the <li> tag.

Unordered Lists :

An unordered list is a list of items. The list items are marked with bullets (typically small black circles).

An unordered list starts with the <ul> tag. Each list item starts with the <li> tag.

Definition Lists :

A definition list is not a list of single items. It is a list of items (terms), with a description of each item (term).

A definition list starts with a <dl> tag (definition list).

Each term starts with a <dt> tag (definition term).

Each description starts with a <dd> tag (definition description).

Unordered List :

ThinkPositve

Never Depressed

Keep Smiling

Ordered List :

1.Fail

2.Work Hard

3.Win

4.Teach

Definition List :

Success Fail First,

Happy Smile

Always

HTML FORMS HTML Forms are used to select different kinds of user input.

A form is an area that can contain form elements.

Form elements are elements that allow the user to enter information like,

1. text fields,

2. textarea fields,

3. drop-down menus,

4.radio buttons,

5. checkboxes,

6. Action Attribute and the Submit Button,etc.

Text Fields:

Text fields are used when you want the user to type letters, numbers, etc. in a form.

Example :

<form>

First name: <input type="text" name="firstname" /> <br />

Last name: <input type="text" name="lastname" />

</form>

First name :

Last name :

OUTPUT :

RADIO & CHECK BOXRadio Buttons :

<form>

<input type="radio" name="sex" value="male" /> Male <br />

<input type="radio" name="sex" value="female" /> Female

</form>

Checkboxes :

<form>

Bike: <input type="checkbox" name="vehicle" value="Bike"/> <br />

Car: <input type="checkbox" name="vehicle1" value="Car"/><br />

</form>

Male

Female

Bike

Car

HTML LAYOUT

A part of this page is formatted with two columns, like a newspaper page.

The trick is to use a table without borders, and maybe a little extra cell- padding.

No matter how much text you add to this page, it will stay inside its column borders.

<table border="0" width="100%" cellpadding="10"><tr>

<td width="50%" valign="top"> This is the Time to save Our Earth to Our Future Generation.So

everybody shoud be a Volunteer. </td>

<td width="50%" valign="top"> For smooth relationship between to us & nature We should do some

activities to Preserve our Earth.</td>

</tr> </table>

This is the Time to save Our Earth to Our Future

Generation.So everybody shoud be a Volunteer.

For smooth relationship between to us & nature We

should do some activities to Preserve our Earth.

HTML FRAMES With frames, you can display more than one HTML document in the same

browser window.

Each HTML document is called a frame, and each frame is independent of the others.

The Frameset Tag

* The <frameset> tag defines how to divide the window into frames

* Each frameset defines a set of rows or columns

* The values of the rows/columns indicate the amount of screen area each row/column will occupy

VERTICAL & HORIZONTAL FRAMESET<html>

<frameset cols="30%,40%,30%"> <frame src="frame_a.htm"> <frame src="frame_b.htm"> <frame src="frame_c.htm">

</frameset></html>

<html><frameset rows="30%,40%,30> <frame src="frame_a.htm"> <frame src="frame_b.htm"> <frame src="frame_c.htm">

</frameset></html>

Reference

Book Reference1. Computer Networks by Andrew S. Tanenbaum, David Wetherall

2. Data Communications And Computer Networks By Prakash C. Gupta

3. Head First HTML with CSS & XHTML  By Elisabeth Freeman, Eric Freeman

4. HTML and CSS: Design and Build Websites By Jon Duckett

Image Reference

5. https://www.google.co.in/search?q=computer+network&hl=en-IN&biw=1517&bih=714&noj=1&tbm=isch&source=lnms&sa=X&ei=6cajVKPUGMLhoATClYKgCw&ved=0CAgQ_AUoAQ&dpr=0.9