The Internet originated as a way to connect computer networks globally in a resilient manner. It has since grown to be a worldwide system of interconnected computer networks that use standard communication protocols like TCP/IP to share data. The Internet provides many services like email, information search, online education, and entertainment. It connects billions of devices worldwide through internet service providers and uses protocols like HTTP, FTP, and SMTP to transfer different types of files and messages.

1. THE INTERNET

2. The Internet
• The Internet: An internet that spans the world
– Original goal was to develop a means of connecting
networks that would not be disrupted by local disasters.

3. The Internet
• An information system
• Communication tool
• A large network of computer systems
world wide
• can be explored by using a Web Browser
• Services available through the Internet:
• Email (Discussion groups , Chat Rooms, etc.)
• Information search (including research)
• Education (Online courses; virtual colleges)
• Entertainment, News, and more…...

4. Internet Architecture
• Internet Service Provider (ISP)
• Access ISP: Provides connectivity to the Internet
– Traditional telephone (dial up connection)
– Cable connections
– Wireless

5. Internet Composition

6. A network protocol
Is the set of very detailed rules, sequences, message
formats, and procedures that computer systems use
and understand when exchanging data with each
other.

7. Examples of Protocols
– Transmission Control Protocol (TCP)
– User Datagram Protocol(UDP)
– File Transfer Protocol (FTP)
– Hypertext Transfer Protocol (HTTP)
– Simple Mail Transfer Protocol (SMTP)

8. Transmission Control Protocol (TCP/IP)
• It is connection oriented.
• It establish connection before data transfer
• It divide the whole message in small parts known as
packets
• It sends packets in order and it also receive in order
in destination

9. User Datagram Protocol(UDP)
• It is not connection oriented.
• It does not establish connection before data transfer
• It divide the whole message in small parts known as
packets.
• It sends packets to the available path on that
particular movement.
• The packets are not received in order and it required
a addition mechanism for ordering the packets on
destination.

10. File transfer protocol
• Is a network protocol used for transfer data from one
computer to another through a network such as
Internet (is commonly used for copying files to and
from other computers)
• FTP is a two-way system - it can be used to copy or
move files from a server to a client computer as well
as upload or transfer files from a client to a server
• FTP systems generally encode and transmit their
data in binary sets which allow for faster data
transfer

11. What is an IP Address?
• An IP address is a unique global address for a
network interface
– An IP address:
- is a 32 bit long identifier
- encodes a network number (network
prefix) and a host number.

12. Network prefix and host number
• The network prefix identifies a network and the host
number identifies a specific host (actually, interface
on the network).
network prefix host number

13. Dotted Decimal Notation
• IP addresses are written in a so-called dotted
decimal notation
• Each byte is identified by a decimal number in the
range [0..255]
• Example:
10000000 10001111 10001001 10010000
1st Byte
= 128
2nd Byte
= 143
3rd Byte
= 137
4th Byte
= 144
128.143.137.144

14. IP Addresses (continued)
• When IP addresses were originally created, they
were called classful addresses
– That is, each IP address fell into particular class
– A particular class address has a unique network address
size and a unique host address size
– There are basically five types of IP addresses: Classes A,
B, C, D and E
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15. IP Addresses (continued)
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16. IP Addresses (continued)
• When you examine the first decimal value in the
dotted decimal notation:
– All Class A addresses are in the range 0 - 127
– All Class B addresses are in the range 128 - 191
– All Class C addresses are in the range 192 – 223
– All Class D addresses are in the range 224 – 239
– All Class E addresses are in the range 240 - 255
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17. Name servers

18. DNS
• IP addresses are difficult to remember
– JohnDoe@140.203.8.22 would be difficult to remember
– If JohnDoe’s mail server moves to another machine, then his e-mail address
would not be valid anymore
– Something like JohnDoe@wuzwuz.ucg.ie would be appropriate
• Need some mechanisms to translate wuzwuz.ucg.ie to the IP address
– To solve this problem DNS was invented
• It is a hierarchical, domain-based naming scheme and a
distributed database system for implementing naming scheme.
• Usage:
– Map name onto an IP address, an application program calls an library
procedure, called resolver.
– The resolver sends packet to a local DNS server which looks up the name and
returns the IP address to the resolver
– The resolver returns the IP address to the application, which can establish an
TCP/IP connection with the destination (or send packets)

19. URL – Uniform Resource Locator

20. URL – Uniform Resource Locator

21. Traditional Internet Applications
• Electronic Mail (email)
– Domain mail server collects incoming mail and transmits
outgoing mail
– Mail server delivers collected incoming mail to clients
via POP3 or IMAP
• File Transfer Protocol (FTP)
• WWW (World Wide Web)

22. World Wide Web (WWW)
– a vast collection of information that’s connected like a
web
– accessible through the Internet using connections called
hyperlinks
– view the WWW resources through a program called a
Web Browser, such as:
• Netscape Navigator
• Internet Explorer
– Navigate through the WWW by pointing to and clicking on
hyperlinks (underlined or boldfaced words, phrases,
icons, or images)
– Also called Cyberspace or the Information Superhighway

23. Architectural Overview
• Browser displays a page on the client machine
– Click on a link, the browser sends a message to the abcd.com web server asking it for the
page
– When page arrives, it is displayed; if it contains a hyperlink on a page on xyz.com, that is
clicked, then the browser will send a message to xyz.com server and the process
continues

24. HTML – HyperText Markup
Language
• (a) HTML source code
– Markup language containing explicit commands for formatting
• (b) Formatted page