Internet Basics 1

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Internet Basics

Review

1

Lyn Belisle


What is the Internet?

It is a collection of computer networks that communicate with each other using a
common set of rules, called a
protocol
.


How the Internet Works


The Internet is a type of network known as a
packe
t
-
switched network
. Data is sent
through the network in small pieces called
packets
.

When two computers communicate
over the Internet, data does not flow directly between them. Instead, it is broken up into
packets which are sent from device to device thro
ugh the network until they reach their
destination. On the receiving end, they are reassembled.


Along the way, devices call
routers

examine the packets and decide what path each
should travel. If a packet is going a long distance, it will probably make it
s way from one
network to another until it reaches one of the very large transmission lines, called the
backbone
, that travel long distances. It will jump off the backbone when it reaches a
network that can link it to its final destination.


Three Importan
t Concepts: TCP/IP, Internet Addresses and the
Domain Name System


TCP/IP and Routing


How do packages actually travel the Internet as they are directed by routers? A protocol
called
TCP/IP

makes it happen.

This is actually a combination of two protocols.
The
Transmission Control Protocol (TCP)

defines how data is broken down into packets
when sending and how they are reassembled at the receiving end. The
Internet Protocol
(IP)

defines how data is routed over the Internet.


When TCP breaks up the data, the
packets are fairly small. A typical packet, called an IP
packet, is less than 1500 characters in length. Part of what TCP does is to create a
collection of information about the IP packet called a
header
, which is attached to the IP
packet. The most import
ant pieces of information in the header are the destination
address and something called a
checksum
.

This is a number that allows the receiving end
of the packet to determine if any errors occurred

during
transmission.


When TCP has an IP packet ready to g
o
, it most likely starts out on a Local Area
Network (LAN). It its destination is outside the LAN, the packet is sent to a router that
connects the LAN to the next network in the path.

The router examines the header and
reads the destination address to see

what path the packet should travel. There may be
more than one route available. When a message is sent, the packets may take different
routes or may arrive in the wrong order. It is then up to TCP to put it all back together.
TCP also verifies the checksu
ms of the packets to make sure no errors occurred.

If a
corrupt packet is found, the destination sends a request for that packet to be sent again.


You can see examples of packets traveling the Internet by using the
tracert

command
. In
Windows, the tracert

command can be accessed from the command line (DOS prompt).
When you use this command, the packet’s route is shown. Each line shows a router along
the way. At the far right of the line is the address of the router.


Using Tracert


1.

Start your connection to

the Internet

2.

Choose
Run

for the
Start

menu

3.

At the
Open

prompt, key
cmd

and click OK. A command prompt will open.


4.

At the prompt, key

tracert and the website (e.g., tracert
www.trinity.edu
)



5.

Perform a trace to anot
her website that you are familiar with, such as yahoo.com
or google.com.


Using Ping


The
ping

command can be used to determine of a device at a specific IP address is
responding. If a computer or device is able to talk to the network, it should respond to

a
ping.


1.

Start your connection to the Internet

2.

At the command prompt, key ping google.com and press Enter. The web server at
google.com will be pinged four times and you will see four replies.


3. In this case, the request was times out but the IP addres
s is shown. You can open a
web site using the IP address.
Noting the IP address
, you would
type in

http://216.239.37.99

in your browser’s address bar

and you would reach google.com.
The IP address

that you typed in

wou
ld show in the
address

bar when the site is
accessed.

Internet Addresses


An Internet address is called an
IP address

because it is an address recognized by IP, the
Internet Protocol. Every device on the Internet has a unique IP address.

The IP address is
a set of four numbers separated by dots (e.g. 216.167.137.235).

You could access web
sites through the IP address, but numbers are harder to remember than a name such as
google.com. It did not take long for Internet pioneers to decide that IP addresses wer
e not
the friendliest way to access Internet destinations. To make it possible to associate names
with the IP address, The
Domain Name System

was devised.


The Domain

Name System groups the many computers on the Internet into domains.
Domains are hierarchi
cal. The top
-
level domains are the well
-
known extensions such as
.com

or
.net
. Within the top level domains are second
-
level domains. Google.com is a
second
-
level domain. When a user enters an address such as
google.com
, computers

called
name servers

look

up the IP address of google.com and direct the email or browser
to that address.


The Internet has thousands of name servers and each one cannot possibly know all of the
Internet’s web addresses. To overcome that, a master database keeps track of what name

servers are the authority for each and every domain name.
For example, if you register
your own domain, part of the registration process requires that you indicate what domain
name servers
(DNS
)

will know where to look for your web site. This database reg
istry
does not know the IP address of your web site, but it knows which name server to ask. So
as long as the domain name registry knows the address of a name server that does know
the correct IP address, and Internet user in the world can find your web si
te.


Who Runs the Internet?


No single organization runs the Internet, and there is no central manager. But there are
some important organizations involved in the cooperative effort. Certain groups establish
the standards that the Internet uses. One of the
se is the Internet Society (ISOC) which
organizes the people who organize the Internet. Check out their website at
http://www/isoc.org
.


A key part of keeping the Internet running smoothly worldwide is ensuring that eve
ry
device on the Internet has a unique address. The Internet Corporation for Assigned
Names and Numbers (ICANN) is a nonprofit corporation that coordinates the assignment
of Internet addresses and domain names. The coordination provided by ICANN keeps the
Internet operating with stability:

http://www.icann.org


The

World Wide Web Consortium is the organization that develops standards for the
World Wide Web. The Web itself is not the same as the Internet


it is a series

of
protocols that run on top of the Internet. The World Wide Web Consortium was founded
in 1994 by Tim Berners
-
Lee and it serves as a source of information for Web developers
and users:

http://www.w3.org


Key Points




A computer network connects computers
so they can communicate and share
resources




The Internet is a network of networks that communicate using a common set of
rules, called a protocol




The Internet is a packet
-
switched network, meaning data is sent in packets that
travel from router to router




The large transmission lines of the Internet are called the backbone




The protocol used for communication on the Internet is TCP/IP. Transmission
Control Protocol (TCP) breaks the data into packets and the Internet Protocol (IP)
defines how data is route
d.




The tracert command displays the route the packet takes over the internet




Every device on the Internet has a unique IP address




The ping command tests for a response from an Internet address




The Domain Name System assigns “friendly” names to the nume
ric IP address.
The computers that translate names into IP addresses are called domain name
servers (DNS)


Key Terms to Know


Backbone

Checksum

Computer network

Domain Name Server

Header

Internet

Internet Protocol (IP)

IP address

IP packet

Local Area Netwo
rk (LAN)

Name server

Network

Packet

Packet
-
switched network

Protocol

Router

Transmission Control Protocol (TCP)