Useful for B. Sc Ag. Students

1. Dr. Md. I. A. Ansari
Department of Agricultural Engineering
Birsa Agricultural University
Kanke, Ranchi
(e-mail: irfan26200@yahoo.com)

2. WHAT IS A NETWORK?
• A network is simply two or more computers
that are linked together.
• The most common types of networks are:
• Local Area Networks (LANS) and
• Wide Area Networks (WANS).
• The primary difference between the two is
that a LAN is generally confined to a limited
geographical area, whereas a WAN covers a
large geographical area. Most WANs are
made up of several connected LANs.

3. Computer Network
• Types
–Local area network (LAN) –
connects computers in close
proximity
–Metropolitan are network (MAN) –
connect computers between
buildings in the same geographic
area
–Wide are network (WAN) – connects
computers over great distances

4. COMMUNICATIONS MEDIA
• Communications Channel
– To transfer data from one computer to another
requires some type of link through which the data can
be transmitted. This link is known as the
communications channel.
– To send data through the channel requires some type
of transmission media, which may be either physical
or wireless.

5. PHYSICAL MEDIA
• Twisted-pair cable – consists of two independently
insulated wires twisted around each other (least
expensive type of cable—the kind that is used in many telephone
systems)
• Coaxial cable – consists of an insulated center wire
grounded by a shield of braided wire (the primary type of
cabling used by the cable television industry; it is more expensive than
twisted pair)
• Fiber-optic cable – contains hundreds of clear
fiberglass or plastic fibers (threads) (made from thin, flexible
glass tubing; bandwidth is greater, so it can carry more data; it is lighter
than metal wires and is less susceptible to interference; it is fragile and
expensive)
• ISDN line – a special digital telephone line that
transmits and receives information at very high
speeds

6. Wireless Media
• Microwave system – transmits data via high-
frequency radio signals through the atmosphere
• Satellite system – receive transmitted signals, amplify
them, and then transmit the signals to the appropriate
locations
• Cellular technology – uses antennae resembling
telephone towers to pick up radio signals within a
specific area (cell)
• Infrared technology – transmits data as infrared light
waves from one device to another, providing wireless
links between PCs and peripherals
Note: The type selected is determined by the type of
network, the size of the network, and the cost.

7. HOW ARE NETWORKS CATEGORIZED?
• Networks are usually classified using
three properties:
• Topology
• Protocol
• Architecture

8. NETWORK
TOPOLOGIES
• Network Topology (or layout) – refers to the way
computers and peripherals are configured to form
networks
– Bus topology – all computers are linked by a single
line of cable
– Star topology – multiple computers and peripheral
devices are linked to a central computer, called a
host
– Ring topology – each computer or workstation is
connected to two other computers, with the entire
network forming a circle
– Hybrid topology – combine network layout
types to meet their needs

9. Network/Communication Protocols
• A protocol is simply an agreed-on set of rules
and procedures for transmitting data between
two or more devices.

10. Network/Communications Protocols
• Most networks use Ethernet, but some
network may use IBM’s Token Ring
protocol.
• On the Internet, the major protocol is
TCP/IP (an acronym for Transmission
Control Protocol/Internet Protocol).

11. EXAMPLE OF AN ETHERNET BUS
• Ethernet LANs use a
bus topology.
• All stations are
connected to a single
long cable.
• Any station can send a
signal along the cable,
which all other stations
will receive. Unlike ring
topologies, the cable
doesn't close a loop.

12. Common Topologies - Star
• In a star network, each node is connected
to a central device called a hub. The hub
takes a signal that comes from any node
and passes it along to all the other nodes
in the network.

13. • The hardwares required to setup a
computer network include network cables,
router, hub and network cards.
• Network Cables: Network cables are
used to connect computers. The most
commonly used cable is Category 5 cable
RJ-45.
•

14. NETWORKING HARDWARE AND SOFTWARE
• Hub – electronic device (with a number of ports) used
in a LAN to link groups of computers
• Repeaters (also called amplifiers) – electronic
devices that receive signals and amplify and send
them along the network
• Routers - electronic devices used to ensure
messages are sent to their intended destinations
• Gateway – consists of hardware and/or software that
allows communications between dissimilar networks
• Bridge – consists of hardware and/or software
that allows communication between two
similar networks

15. HUBS

16. Repeaters
The repeater amplifies the electrical signals and resends the data.
A common problem in the networking world is that of weakening electrical
signals. Electrical signals traveling through wires (such as copper wires used in
most networks), weaken due to the wire's electrical resistance. This effect limits
the lengths of the cable that can be used. A repeater will overcome this limit,
when there is a need to connect two computers at a larger distance.
A repeater is connected to two cable segments. Any electrical signal reaching
the repeater from one segment, will be amplified and retransmitted to the other
segment.

17. Routers

18. GATEWAY
The term gateway now refers to special-
purpose devices, that perform protocol
conversions. Gateways implement application
layer conversions of information received from
various protocols.
Integrated Services Digital Network (ISDN) is a set
of communication standards for simultaneous digital
transmission of voice, video, data, and other network
services over the traditional circuits of the public
switched telephone network.

19. MODEMS
An illustration of data sent using a modem and a regular
telephone line.
A modem is a device that converts digital data originating from a
terminal or computer, to analog signals used by voice communication
networks such as the telephone system. At one end, modems convert the
digital pulses to audible tones and convert audio tones back to digital
pulses at the other.
The word "Modem" stands for "MOdulator-DEModulator".

20. Modems
• Transmission speed
Modems are available in different transmission speeds, which
are measured in BPS (bits per second) also called BAUD rate.
Standard modems speeds: 9600 baud, 14400 baud, 28800
baud, 33600 baud, 56800 baud.
• Internal/External
Internal modems are electronic cards. An internal modem is
installed in one of the computer's expansion slot.
External modems are fully functioning external devices. The
external modem is connected to a computer using a serial
cable to one of the computer's serial ports, and draws power
from an external power source.

21. EXAMPLE OF FIREWALL
• Firewalls are systems that establish access control
policies among networks. They can block information
from entering a network or from getting out of that
network, they can permit different users to perform
different kinds of operations, according to the user's
authorizations.

22. Network Architecture
• Network architecture – refers to the way a
network is designed and built. The two major
types are:
– Peer-to-peer architecture – Computers connect
with each other in a workgroup to share files,
printers, and Internet access. This is used to
connect a small number of computers.
– Client/server architecture – sends information from
a client computer to a server, which then relays the
information back to the client computer, or to other
computers on the network

23. Communication Protocols
File transfer protocol (FTP) – used to
transmit files.
Simple mail transfer protocol (SMTP) –
used to transmit e-mail messages.
Post office protocol (POP) – allows the
recipient to retrieve messages.
Wireless application protocol – enables
wireless devices to access and use the
Internet using a client/server network.

24. Data Transmission Characteristics
• Bandwidth (rate of transmission)
• Analog or Digital (type of signal)
– Analog transmission – takes the form of continuous
waves transmitted over a medium at a certain
frequency rage
– Digital transmission – sends data in the form of bits
• Serial or Parallel (order of bits)
– Serial transmission – all of the data bits are
transmitted one bit after another in a continuous line
– Parallel transmission – data bits are sent at the same
time along multiple paths

25. Data Transmission Characteristics
• Bandwidth (rate of transmission)
• Analog or Digital (type of signal)
– Analog transmission – takes the form of continuous
waves transmitted over a medium at a certain
frequency rage
– Digital transmission – sends data in the form of bits
• Serial or Parallel (order of bits)
– Serial transmission – all of the data bits are
transmitted one bit after another in a continuous line
– Parallel transmission – data bits are sent at the same
time along multiple paths

26. Communications Software
• E-Mail Software – used to send and receive
electronic messages using the Internet
• Web Browser – allows users to access and
view Web pages

27. Getting Connected
• User’s computer must connect to a server
• Server must communicate using TCP/IP
• The user can purchase access to a server
from an ISP (Internet Service Provider)

31. Web Addresses
 Each computer on the Internet has an unique
identification number, called an IP (Internet
Protocol) address.
 The IP addressing system currently in use on
the Internet uses a four-part number.
 Although each computer connected to the
Internet has a unique IP address, most Web
browsers use domain name addressing to locate
Web sites and pages.

32.  The standard way to give the address of any
resource on the Internet that is part of the World
Wide Web
 (WWW). A URL looks like this:
 http://www.bauranchi.org

34. • What is a Web Browser?
 A Web browser contains the basic software you need in
order to find, retrieve, view, and send information over the
Internet.
 This includes software that lets you:
 Send and receive electronic-mail (or e-mail) messages
worldwide nearly instantaneously.
 Read messages from newsgroups (or forums) about
thousands of topics in which users share
 information and opinions.
 ▪ Browse the World Wide Web (or Web) where you can
find a rich variety of text, graphics, and interactive
information.
 The most popular browsers are Microsoft Internet Explorer
and Netscape Navigator .
 The appearance of a particular Web site may vary slightly
depending on the browser you use.

35. Types Of Browsers
 Netscape Navigator
 Mozilla Firefox
 Internet Explorer
 Opera
 Safari

36. • Internet Service Provider (ISP): • An
Internet Service Provider (ISP) is a
company that allows user to use their
internet connection for a price. When you
register with an ISP the followings are
given: – Username and Password. Some
popular Internet service providers in India
are : VSNL (Videsh Sanchar Nigam
Limited, MTNL (Mahanagar Telecom
Nigam Limited), – BSNL (Bharat Sanchar
Nigam Limited), Airtel, Reliance, etc.

38. Microsoft Internet Explorer Window

40. • 1. Back. Lets you return to pages you've viewed, beginning with the most
recent. Right-click the Back button and select from a list of recently visited
sites.
• 2. Forward. Lets you move forward through pages you've viewed using
the Back button. Right-click the Forward button and select from a list of
recently visited sites.
• 3. Stop. Halts the process of downloading a Web page. Click this if you
want to stop downloading a
• page for any reason for example, if you're having trouble downloading it or
if you don't want to wait
• for it to download. Then try downloading it again or browse elsewhere.
• 4. Refresh. Updates any Web page stored in your disk cache with the latest
content. When you return to a page that you've visited, your browser
displays the file stored in your disk cache, rather than the current page on
the World Wide Web. If a web page doesn't come up the whole way or is
taking abnormally long to load, try the Refresh or Reload button -
sometimes this will load the page better.
• 5. Home. Returns you to your home page. You can designate any Web
page as your home page.
• 6. Search. Displays a choice of popular Internet search engines in the left
pane. Your search results appear in the left pane, too.

41. • 7. Favorites. Displays a list of the sites you have marked. Click any item
in the list to jump to it.
• 8. History. Shows a list of Web sites you've visited.
• 9. Mail. Connects you to the Microsoft Outlook Express messaging and
collaboration client so you can
• read e-mail and newsgroup messages.
• 10. Print. Prints the page you're viewing. This is one way to save
information from the Internet so that
• you don't have to reconnect to view it again. You can even print the URL
associated with each
• hyperlink, making it easy to navigate to the site later.
• 11. Edit. Opens a file in the Microsoft Word word processor that contains
the HTML code for the page you're viewing so you can see and even edit
it.

42. What is E-mail?
 E-mail (electronic mail) is the exchange of computer-stored
messages by telecommunication.
 E-mail can be distributed to lists of people as well as to
individuals.
 However, you can also send non-text files, such as graphic
images and sound files, as attachments sent in binary streams.
 “E-mail is text-based mail sent via the computer from one
person to another.”
 “E-mail is an ideal method for sending documents already on
your computer using attachments.”
 “E-mail is a way to communicate with people as close as your
office or as far away as the other side of the world.”

43. How E-mail Works

44. How E-mail works

45.  E-mail messages can go to only one recipient or
to dozens of recipients at once.
When you send a message, it travels
through the network to an e-mail server.
The e-mail server stores messages until
the recipient(s) request them.

46. Key E-mail Features
 Email is the simplest and one of the most effective technologies for sharing
knowledge at a distance.
 E-mail is One-to-Many
 Email is the most effective and powerful technology for
knowledge management.
 For many Internet users, electronic mail (e-mail) has
practically replaced the Postal Service for short written
transactions.
 Electronic mail is the most widely used application on the Net.
 You can also carry on live "conversations" with other
computer users, using Internet Relay Chat (IRC).
 More recently, Internet telephony hardware and software
allows real-time voice conversations.
 Email is almost free and fast.

47. Electronic Mail
 Send mail electronically via the Internet
 Requires an account on a mail server and supporting
software on your PC
 The username and password will allow you to access
your account
 All e-mail programs allow you to Send, Compose, Reply,
and Forward mail
 message provided user has an e-mail address. The
general format of internet e-mail address is:
 username@domainname.coIn e-mail facility, any user
on a network can send or receive message provided
user has an e-mail address. The general format of
internet e-mail address is:
 username@domainname.com
 In e-mail facility, any user on a network can send or
receive m

48. Anatomy of an Email message
 To contains the e-mail addresses of
 the recipients. This is a mandatory entry.
 CC: short for Carbon Copy. This is optional.
 BCC: short for Blind Carbon copy

49.  Subject contains the main topic of the message. Keep
this brief.
 Recipients see this in their summary of incoming e-
mails.
 Attachment contains the names of files that you may
be sending, for example, a word-processing
 document or a spreadsheet.
 Body contains the message itself.

50. Signatures
 E-mail can include a signature at the end of the message.
 An e-mail signature is not your hand-written signature.
 Like a business card, an e-mail signature can include your
name, title, telephone and fax numbers, street address, and e-
mail address.
 It saves time, you don’t have to retype the information each
time you send a message.
 Clicking the feature automatically adds it to the message.

51. Reading Email messages
 Messages are organized in folders or boxes.
 Received mail is kept in an Inbox
 outgoing mail is stored in an Outbox;
 sent mail is filed in a Sent box.
 To read an e-mail, double-click on the envelope icon
or the Subject line of the message. This opens a new
window containing the header and body of the
message.

52. Replying to Email messages
 The window with the e-mail you are reading has a Reply or Re
button. Click on this button to open a new window. The To
 and Subject lines are automatically filled
 in with the e-mail address of the sender
 and the subject of the message.
 the text of the original e-mail appears in
 the body of the reply, usually marked in a
 different font or color, or with a special
 character, such as the greater than sign
 (>) at the beginning of each line.

53.  e-mail programs allow you to attach word-processing
documents, spreadsheets, graphics, audio, video, and
other electronic files to your message.
 To attach a file:
 Click on the Attachment or
 Include File icon, often represented by a paper clip.
Select the file you want from the file attachment
window.

54. Opening attachment
 Open or save an attached file by double-clicking
on the icon for the file.
 Caution: Your computer can contract a virus
when you open an attached file. If you do not
know or trust the person who sent the e-mail.
 delete the attachment to avoid infection

55. • Privacy of Email
 Not a secure form of communication
 Don’t send secret or confidential
 information
 Credit Card information
 Social Security number
 Passwords
 More like a postcard than a sealed letter
 Think before you forward
 Do you have the sender’s permission?

57. An E-mail Address
Every e-mail address is unique and
consists of two parts, a user name and a
host computer
The @ sign is required

58.  The domain name, which comes after the
symbol @, may also include an extension other
than .com which stands for commercial
business. It may be an educational institution
(“edu”), an organization (“org”) or government
department (“gov”).
 There are various companies or web sites that
provide free email addresses that you can use at
your convenience and that allow you to access
your messages from any computer connected to
the internet. Some of these companies are
Yahoo, Rediff, Lycos, Netscape, and Hotmail.

59. • Composing/ Sending an E-mail message
• To compose an e-mail message, click on the ‘Compose’
button. You will get an empty mail form, which will have
the following parts as shown
• You will have to fill in the various components as shown
below:
• To – Enter the E-mail address of the person(s) to whom
the message has / have to be sent.
• Cc - Enter the e-mail address of the person(s) to whom
the copy of the message has / have to be sent.
• Bcc - Enter the e-mail address of the person(s) to whom
the blind copy of the message has / have to be sent.
• Subject – Enter a brief description/title of the message.
• Body – Enter the actual message here.

60. • Address Book
• An address book is a place where you can store the
information about the people to whom you write. The
advantage of having a person’s details in the address
book is that you don’t have to key-in those details
each and every time you send a message.
• Signature
• The signature can be anything from your name and
address or contact information. You can program
yours system in such a way that all out going message
will have your signature at the end of the message.

61. • File Attachment Facility
• One major drawback of e-mail is that you cannot send
formatted text. So you can send the formatted text in the form
of file as an attachment to the mail. You can attach any file to
a mail that you want to send by clicking on the ‘attach’ button
and selecting the desired file.
• Replying and Forwarding E-Mail Messages
• You can reply to an e-mail by pressing ‘Reply’ button. You
need not to type the address or the subject, the programs are
intelligent enough to automatically put the address of the
person whose mail you are replying to, prefix the subject with
‘Re:’ to indicate that it is a reply.

62. • You can forward a message that you have
received by clicking ‘Forward’ button. The
difference between replying and forwarding is
that you reply to the person who has sent the
mail, but you can forward a message to anybody
you like. The message that is being forwarded
will be marked with a ‘>’ symbol as in the case of
replying. You will have to enter the e-mail ID of
the person(s) to whom the message is
forwarded.

63. • Sending to Multiple Recipients:
• Although e-mail was originally designed as a way for two
people to communicate, most e-mail systems allow a user to
send a message to multiple recipients. To do so, the sender
specifies multiple mailbox addresses on the To line of a
message. The system sends one copy of the message to each
recipient. For example,
• To: akd@agfe.iitkg.ac.in, sp@ agfe.iitkg.ac.in,
hd@agfe.iitkg.ac.in
• From:xyz@baujharkhand.org
• Subject:------------
• Message
• The To line in the header specifies three recipients and each of
the three will receive a copy of the message.

64. E- Mail Web Sites
• www.rediffmail.com
• www.yahoo.com
• www.123india.com
• www.indiatimes.com
• www.email.com
• www.lycos.com
• www.hotmail.com
• www.gmail.com

70. Opening Email Account