Transcript What is the Internet?

Introduction to Information Technology
Lecture 9
The Internet
Dr. Ken Tsang 曾镜涛
Email: [email protected]
http://www.uic.edu.hk/~kentsang/IT/IT3.htm
Room E408 R9
1
With thanks to Dr. Haipeng
Guo
Outline
What is the Internet?
 History of the Internet
 How to connect to the Internet
 How the Internet works
 Software and services supported by
the Internet





WWW
Email
FTP
Search Engines
2
What is a Network?

Collection of computers and devices
connected to share information and
resources
3
What is a LAN?


Local Area Network
Network in limited geographical area such
as home or office building
4
What is a WAN?


Wide Area Network
Network that covers large geographic
area using many types of media
5
What is the Internet?

A network of computer networks worldwide

The Internet is world’s largest WAN

Also called the information highway, the net,
or cyberspace
6
History of the Internet
1957 - the USSR launched Sputnik, the
first artificial earth satellite
1958 - In response, the US Department of Defense
established the Advanced Research Projects Agency
(ARPA)
Several years later ARPA began to focus on
computer networking and communications technology 7
Idea of Package Switching

In 1961, Dr. Leonard Kleinrock created the
basic principles of packet switching, the
technology underpinning the Internet, while
a graduate student at MIT
First node
on the Internet
8
ARPANET


In 1969 ARPANET was constructed
It is a network of four computers




UCLA
SRI (Stanford)
UCSB
University of Utah
The first message: lo….gin
9
Internet Today



The Internet has grown from four host
computer systems to many millions
By 1984, ARPANET had more than 1,000
individual computers linked as hosts
In 1992, the Web Wide Web protocol was
released



ARPANET had more than 1 million computers
linked as hosts
Today, more than 150 million hosts connect to
the Internet
In 2005, China’s Internet population was 111
10
million
Who owns the Internet?




Nobody owns the Internet!
It doesn't mean it is not monitored and
maintained in different ways
The computers and devices connected to the
Internet belong to a person or an organization
The Internet Society, a non-profit group
established in 1992, oversees the formation of
the policies and protocols that define how we
use and interact with the Internet
11
Connecting to the Internet

At home




At office


Through Phone modem
Through DSL / ADSL
Through Cable modem
Through LAN
Wireless connection

Through hotspots
12
The Internet Backbone
• Typically fiber optic lines
• 5 Mbps to over 600 Mbps
• Provided by companies such as AT&T, GTE, and IBM
13
ChinaNet: the largest Internet
backbone in China
• Owned by China Telecom
• 336 Mbps connection to the Global Internet
14
ChinaNet: the largest Internet
backbone in China
• Chinese Education and Research network
• 8 Mbps connection to the Global Internet
15
Internet Service Provider (ISP)
User PC
Network Access Point
16
Connecting via Phone Modem
A computer
Username and password
and a number to dial up to
the ISP’s computer
A phone modem card
Connecting to a phone jack
Usually 64 kbps (bits per second) at most
17
Connecting via DSL/ADSL
DSL:
Digital Subscriber Line

ADSL:
Asymmetric DSL


Downloading faster
than uploading
18
Cable Modem
DSL and Cable Modem connections
are both broadband connections
Faster than 128 kbps
19
Connecting via LAN
A computer
network card
Hub or switch or router
20
DSL and telephone-related terminologies






NAP – Network Access Point
POP - Point of Presence
POTS - Plain Old Telephone Service
ISDN - Integrated Services Digital Network
PSTN - Public Switched Telephone Network
TELCO - Telephone Company
21
Wireless Connection
Wireless adapters can
plug into a computer's
PC card slot
A wireless router send signals to
wireless devices and has a wire to
send signals to the Internet
22
How the Internet works



Every computer connected to the Internet
must have a unique address.
This is called the IP address.
IP stands for Internet Protocol
Internet
1.2.3.4
5.6.7.8
23
IP Address

An IP address can be split into


network address, which specifies a specific
network
host number, which specifies a particular
machine in that network
24
Try it – ipconfig & ping
25
Domain Name System (DNS)
A hostname consists of the computer
name followed by the domain name
 uic.edu.hk is the domain name



A domain name is separated into two or
more sections that specify the organization,
and possibly a subset of an organization, of
which the computer is a part
Two organizations can have a computer
named the same thing because the domain
name makes it clear which one is being
referred to
26
Domain Name System

The very last section of the domain is called
its top-level domain (TLD) name
27
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
28
Domain Name System

The domain name server is used to
translate hostnames into numeric IP
addresses



it 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
29
nslookup
30
Client/Server Model
All of the machines on the Internet
are either servers or clients.
Web server, e-mail server, DNS server,
ftp server, game server……
31
How data travels the Internet


Messages are divided into fixed-sized,
numbered packets
Network devices called routers are used to
direct packets between networks
32
Routers
Routers determine the path between you
and an Internet server
33
Try it – Tracert (trace route)
34
Network Protocols


Network protocols are layered such that
each one relies on the protocols that
underlie it
Sometimes referred to as a protocol stack
35
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
36
High-Level Protocols

Other protocols built 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)
37
Internet Applications: WWW


World Wide Web
Worldwide collection of electronic documents
web browser
web server
38
Internet Applications: E-mail



E-mail address: [email protected]
e-mail client
E-mail server


SMTP server
POP3 server
SMTP
(Simple Mail Transfer Protocol)
Server handles outgoing mail
Sending email
39
Internet Applications: E-mail

Receiving the email
POP3 (Post Office Protocol) server
handles incoming mails
When you check your e-mail, your e-mail client program
connects to the POP3 server
40
Internet Applications: FTP
FTP stands for File Transfer Protocol
 FTP client program
 FTP server
 Basic steps





Connect to the FTP server
Navigate the file structure to find the file
you want
Transfer the file
41
End the file transfer session
FTP Commands
42
Example of using FTP
43
Internet Applications:
Search Engine
Examples: Google, Baidu
 Web crawling: Search engines use
software called spiders to build lists of
the words found on Web sites
 Indexing: Keep an index of the words
found, and where they
 Searching: User builds a query and
submits it to the search engine

44
Web Crawling
45
Indexing
46
Searching
47
Summary




What is the Internet
History of the Internet
How to connect to the Internet
How the Internet works


Client/Server Model, IP Address, DNS, TCP/IP
Applications on the Internet

WWW, Email, FTP, Search Engine
48

PDF, notes and glossary on the web:
http://www.uic.edu.hk/~davetowey/teaching
/CS/it1010/lectures/10.The.Internet.pdf
http://www.uic.edu.hk/~davetowey/teaching
/CS/it1010/lectures/2x2_10.The.Internet.p
df
http://www.uic.edu.hk/~davetowey/teaching
/CS/it1010/lectures/10.Glossary.pdf
http://www.uic.edu.hk/~davetowey/teaching
/CS/it1010/lectures/10.The.Internet.notes.
html
49