A computer network connects two or more computers together to allow sharing of resources and communication between users. A local area network (LAN) connects computers within a single building or site, while a wide area network (WAN) connects multiple LANs over a larger geographic distance. The Internet is a global system of interconnected computer networks that uses standard protocols like TCP/IP to link billions of devices worldwide. Key applications on the Internet include email, file transfer, remote access, and the World Wide Web, which allows accessing and sharing information through web pages on browsers.

1. COMPUTER
NETWORKS

2. COMPUTER NETWORK
 A computer network is an interconnection of various
computer systems located at different places
 Two or more computers are linked together with a
medium and data communication devices for the
purpose of communicating data and sharing resources
 The computer that provides resources to other
computers on a network is known as server.
 Individual computers in the network, which access
shared network resources, are known as nodes.

3. Networking
 Computer networks have opened up an entire
frontier in the world of computing called the
client/server model
Client/Server interaction

4. Networking
 File server A computer that stores and manages files for
multiple users on a network
 Web server A computer dedicated to responding to
requests (from the browser client) for web pages

5. Local Area Network (LAN)
 Networks used to interconnect computers in a single room,
rooms within a building or buildings on one site are called
Local Area Network (LAN).
 LAN transmits data with a speed of several megabits per
second
 The transmission medium is normally coaxial cables.
 LAN links computers, in the same area for the purpose of
sharing information.
 Usually LAN links computers within a limited geographical area
because they must be connected by a cable, which is quite
expensive.
 People working in LAN get more capabilities in data
processing, work processing and other information exchange
compared to stand-alone computers.

6. Characteristics of LAN
 every computer has the potential to communicate
with any other computers of the network
 high degree of connection between computers
 easy physical connection of computers in a
network
 inexpensive medium of data transmission
 high data transmission rate

7. Use of LAN
 File transfers and Access
 Word and text processing
 Electronic message handling
 Remote database access
 Personal computing
 Digital voice transmission and storage

8. Wide Area Network
 The term Wide Area Network (WAN) is used
to describe a computer network spanning a
regional, national or global area.
 For example, for a large company the head
quarters might be at Cairo and regional
branches at Mansoura, Tanta , and Aswan.
 the transmission medium used are normally
telephone lines, microwaves and satellite
links

9. The characteristics of WAN
 Communication Facility: For a big company spanning over the
country the employees can save long distance phone calls and
it overcomes the time lag in overseas communications.
 Computer conferencing is another use of WAN where users
communicate with each other through their computer system.

10.  Remote Data Entry is possible in WAN. It means sitting at
any location you can enter data, update data and query
other information of any computer attached to the WAN
 Centralized Information: This means if the organization is
spread over many cities, they keep their important
business data in a single place. WAN permits collection of
this data from different sites and save at a single site
 Ethernet: Ethernet developed by Xerox Corporation is a
famous example of WAN

11. Difference between LAN and WAN
1) LAN is restricted to limited geographical area of few kilometers.
But WAN covers great distance and operate nationwide or even
worldwide.
2) In LAN, the computer terminals and peripheral devices are
connected with wires and coaxial cables. In WAN there is no
physical connection. Communication is done through telephone
lines and satellite links.
3) Cost of data transmission in LAN is less because the transmission
medium is owned by a single organization. In case of WAN the
cost of data transmission is very high because the transmission
medium used are hired, either telephone lines or satellite links.
4) The speed of data transmission is much higher in LAN than in
WAN. Few data transmission errors occur in LAN compared to
WAN.

12. Types of Networks
• Local-area network (LAN) A network that connects a
relatively small number of machines in a relatively close
geographical area

13. Types of Networks
• Various configurations, called topologies, have been used to
administer LANs
– Ring topology A configuration that connects all nodes in a closed loop
on which messages travel in one direction
– Star topology A configuration that centers around one node to which all
others are connected and through which all messages are sent
– Bus topology All nodes are connected to a single communication line
that carries messages in both directions

14. Types of Networks
• A bus technology called Ethernet has become the
industry standard for local-area networks
Various network topologies

15. Types of Networks
• Wide-area network (WAN) A network that connects two or more
local-area networks over a potentially large geographic distance
Often one particular node on a LAN is set up to serve as a gateway to
handle all communication going between that LAN and other networks
Communication between networks is called internetworking
The Internet, as we know it today, is essentially the ultimate wide-area
network, spanning the entire globe

16. Types of Networks
• Metropolitan-area network (MAN) The
communication infrastructures that have
been developed in and around large cities

17. Types of Networks
Local-area networks connected across a distance to create a wide-
area network

18. INTERNET
 The Internet is a network of networks
 Computer users on the Internet can contact one
another anywhere in the world
 In Internet a huge resource of information is
accessible to people across the world
 Information in every field starting from education,
science, health, medicine, history, and geography to
business, news, etc. can be retrieved through
Internet
 You can also download programs and software
packages from anywhere in the world

19. Origin of Internet
 In 1969 Department of Defense (DOD) of USA started
a network called ARPANET (Advanced Research
Projects Administration Network )
 Around 1970, NSFNET (National Science Foundation
Network) was created. With the advancement of
modern communication facilities,
 By 1990 many computers were looking up to NSFNET
giving birth to Internet

20. Internet functions
 Internet is not a governmental organization.
 The ultimate authority of the Internet is the Internet
Society.
 This is a voluntary membership organization whose
purpose is to promote global information exchange.
 Internet has more than one million computers
attached to it.

21. E-mail
 E-mail stands for electronic mail.
 This is one of the most widely used features of Internet.
 In electronic mail the data are transmitted through Internet and
therefore within minutes the message reaches the destination may it be
anywhere in the world.
 Therefore the mailing system is excessively fast and is being used widely
for mail transfer

22. Features of E-mail
 One-to-one or one-to-many communications
 Instant communications
 Physical presence of recipient is not required
 Most inexpensive mail service, 24-hours a day and seven days
a week
 Encourages informal communication

23. Components of an E-mail Address
 As in the case of normal mail system, e-mail is also
based upon the concept of a recipient address.
 The email address provides all of the information
required to get a message to the recipient from
anywhere in the world. Consider the e-mail ID
 john@hotmail.com

24. john@hotmail.com
 In the example above, "john" is the local
part, which is the name of a mailbox on the
destination computer, where finally the mail
will be delivered.
 Hotmail is the mail server where the
mailbox "john" exists,
 .com is the type of organization on net
 .edu Educational institutions
 .gov Government site

25. File Transfer Protocol (FTP)
 File Transfer Protocol, is an Internet utility software
used to upload and download files.
 It gives access to directories or folders on remote
computers and allows software, data and text files to
be transferred between different kinds of computers.
 FTP works on the basis of same principle as that of
Client/Server.

26.  FTP "Client" is a program running on the your
computer that enables you to talk to, and get stuff
from, remote computers.
 The FTP client takes FTP commands and sends them
as requests for information from the remote
computer or known as FTP servers.
 To access remote FTP server it is required but not
necessary to have an account in the FTP server.
 When the FTP client gets connected

27. The objectives of FTP
 The basic objectives of FTP are
 to give flexibility and promote sharing of computer programs,
files and data
 to transfer data reliably and more efficiently over network
 to encourage implicit or indirect use of remote computers
using Internet
 to shield a user from variations in file storage systems among
hosts

28. Telnet (Remote Computing)
 Telnet or remote computing is telecommunication utility
software, which uses available telecommunication
facility and allows you to become a user on a remote
computer.
 Once you gain access to the remote computer, you can
use it for the intended purpose.
 The TELNET works in a very step by step procedure. The
commands typed on the client computer are sent to the
local Internet Service Provider (ISP), and then from the
ISP to the remote computer that you have gained
access.
 Most of the ISP provides facility to TELNET into your
own account from another city and check your e-mail
while you are traveling or away.

29. WORLD WIDE WEB (WWW)
 WWW is the short form for the World Wide Web. It is also
commonly known as ‘The Web’.
 The WWW is hypertext based information retrieval tool.
 One can easily surf the Web by jumping from one document to
another using the links in those documents.
 These documents can be in many formats, such as text,
graphics, animation, sound and latest is video. They may also be
a combination of all these.
 All the information on Internet are presented to the user as a
document or more popularly known as Web Page.
 All these Web Pages are link to each other or even to section
within a Web Page. And these links are known as Hyper Links.

30. The Web browser
 The tool used to view these Web Pages on Internet is
known as Internet browser or simply browser.
 It is a software program specifically developed to
extract information on user request from the Internet
and present them as a Web Page to the viewer
 The most popular are Internet Explorer from Microsoft
and Netscape from Netscape Inc

31. Network Protocols
• Network protocols are layered such that
each one relies on the protocols that
underlie it
• Sometimes referred to as a protocol
stack
Layering of key network protocols

32. TCP/IP
• TCP stands for Transmission Control Protocol
TCP software breaks messages into packets, hands them off to
the IP software for delivery, and then orders and reassembles
the packets at their destination
• IP stands for Internet Protocol
IP software deals with the routing of packets through the maze
of interconnected networks to their final destination

33. TCP/IP (cont.)
• UDP stands for User Datagram Protocol
– It is an alternative to TCP
– The main difference is that TCP is highly reliable, at the cost of
decreased performance, while UDP is less reliable, but
generally faster

34. High-Level Protocols
• Other protocols build on the foundation established by the
TCP/IP protocol suite
– Simple Mail Transfer Protocol (SMTP)
– File Transfer Protocol (FTP)
– Telnet
– Hyper Text Transfer Protocol (http)

35. MIME Types
• Related to the idea of network protocols and
standardization is the concept of a file’s MIME type
– MIME stands for Multipurpose Internet Mail Extension
– Based on a document’s MIME type, an application program can
decide how to deal with the data it is given

36. MIME Types
Some protocols
and the ports
they use

37. Firewalls
• Firewall A machine and its software that serve as a
special gateway to a network, protecting it from
inappropriate access
– Filters the network traffic that comes in, checking the validity of
the messages as much as possible and perhaps denying some
messages altogether
– Enforces an organization’s access control policy

38. Firewalls
A firewall protecting a LAN

39. Domain Name System
• The very last section of the domain is called its
top-level domain (TLD) name
Top-level domains, including some relatively new ones

40. Domain Name System
• Organizations based in countries other than the United States use
a top-level domain that corresponds to their two-letter country
codes
Some of the top-level domain
names based on country codes

41. Domain Name System
• The domain name system (DNS) is chiefly used to
translate hostnames into numeric IP addresses
– DNS is an example of a distributed database
– If that server can resolve the hostname, it does so
– If not, that server asks another domain name server

42. THANKS!
Dr Pankaj Gupta
Head – ACCESS Health Digital
digital.health@accessh.org
Twitter: @pankajguptadr, @accesshdigital
LinkedIn: drpankajgupta, accesshdigital