internet basics

Subject: Web Design and Programming Lecturer: Ahmed Ali Saihood
Thi-Qar University, Collage of Computer sciences and Mathematics,
Chapter 1
Internet Basics
Topics:
a. Basic Concepts
b. Communicating on the Internet
c. Internet server Identities
d. Establishing connectivity on the internet
e. Brief Overview TCP/IP and its Services
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I. Basic Concepts
The internet consists of two types of computers Servers and Clients:
 Computers which offer information to be read are called Servers.
 Computer that read the information offered are called Clients.
Servers run special software (Web Server Software) that allow them to
 Respond to client requests for information.
 Accept data from clients.
Some of the most popular software which servers run to allow them
respond to clients requests for information is:
 Internet Information Server.
 Apache.
 Microsoft personal web server.

II. Communicating on the Internet
 TCP/IP is the only protocol used to send data all around the
internet.
 TCP/IP is really two individual sections
TCP: a set of communication protocols.
IP: a unique address.
 Every machine connected to the internet must have an address by
which it can be located on the internet, this called IP address of
the machine.
 For the internet function, no two machines can have the same IP
address; hence each machine connected to the internet must have
unique IP address which identifies that machine.
 The Internet is worldwide network of networks.
 InterNIC is international body located in USA which located
unique IP addresses to organizations liked to the internet, it is
responsible for registering and assigning unique IP address to
organizations wishing to manage networks which will be part of
the internet.
 Unique IP address points to an actual computer connected via
gateway to the internet. This computer known as Domain (place
where information is available) this is called physical domain on
the internet.
 Servers which has a permanents IP address(physical domain) can
provides :
1. A gateway to other computers to access internet. And/or
2. Provide information for internet clients to read. And/or

3. Provide a physical location on which several Virtual
Domain can be hosted.
III. Internet Server Identifies
InterNIC is register and issue unique IP address to internet servers, and
also authorizes organizations to issue IP address in other countries.
As number of Domain registration id grew up InterNIC began
segregating domains according to the services provided by the domain
being registered, this was done by adding an extension to the domain
name. the extension to the domain name indicated the kind of service
being provided by that domain.
.edu Servers that provide educational services
.gov Servers that provide information about countries
.mil Servers that provide military information
.org Servers that provide information about organization in the
world
.com Servers providing commercial services on the internet
IV. Establishing Connectivity on the Internet
 The protocol used to setup communications between a clients and
servers on internet is TCP/IP.
 TCP/IP breaks up data into datagrams and guarantees that the data
is correctly received at its destination.

Client IP address :
How Client IP addresses are assigned?
 Computers that only read information offered (internet clients)
needs not necessarily have a permanent IP address.
 When internet clients logged into internet, clients requires a unique
IP address this IP enable the internet server called to reply
accurately.
 The Internet Service Provider (ISP) server via which the client
connects to the internet temporarily assigns a unique IP address to
the clients.
How ISP achieve the task of assigning IP addresses?
 Assuming that the client computer is windows machine its TCP/IP
stack is configured to get IP address dynamically from the ISP
Server.
 The client computer logs into ISP server , after a successfully login
is accomplished the ISP server automatically passes one IP address
from the block IP addresses in the Server to computer logged in.
 Once computer is logged on the internet a unique IP address is
assigned and any other computer on the internet that aware of this
IP address can setup communications with it.
How IP addressing came into existence?
 One master server called (root) held the entire set of computer IP
addresses.
 The IP addresses were held as pure text in file called Hosts held in
sub-directory on the root server.
 The contents of the Hosts are as follows:

IP address Domain Name
202.100.17.33 Microsoft
Unique IP address of internet server, followed by single Tab character,
followed by domain name.
 When any clients wishes to communicate with any internet server
using browser software, the client sends out a broadcast using the
server’s Domain Name as identifier.
 The ISP server intercepts this request first.
 The ISP server will rout this broadcast to an InterNIC root server.
 In the InterNIC root server’s host file, the domain name will be
mapped into IP address.
 The IP address will be returned to the ISP server.
 The ISP server will now pass this IP address back to client’s
browser.
 The client browser will now broadcast a request to connect directly
to the internet server using IP address.
 As soon as this call is heard by the internet server it will respond
and link will be setup between the client and internet server.
 Web server software running on the internet server takes care of
connecting client to the virtual domain as required.
 Once client is connected to appropriate domain, the web server
software delivers the client the first HTML page of that domain
which is traditionally index.html or index.htm and browsing the
specific domain can begin.
The structure of an internet address:
The structure of an internet server’s address keyed into client’s browser
software is as follows:

http://www.microsoft.com
Where:
http is the communication protocol to be used.
www is the notation for the world wide web.
microsoft is the registered domain name associated with IP address of
an internet server, and
com is the server provides commercial services to clients who connects
to it.
To help speed up access, its IP address can be directly used like
127.57.13.1 instead of the domain name, microsoft.com. In this case no
name resolution needs to take place.
V. TCP/IP and its Services
What are TCP/IP and the Internet?
 The Internet Protocol Suite (commonly known as TCP/IP) is the
set of communications protocols used for the Internet and other
similar networks.
 It is named from two of the most important protocols in it:
 the Transmission Control Protocol (TCP) and
 the Internet Protocol (IP), which were the first two
networking protocols defined in this standard.

TCP/IP layers
 application layer
 transport layer
 internet layer
 data link layer
 physical layer
The physical layer: is pure hardware in any network infrastructure, this
includes the cables, satellite , or any other connection medium, and the
network interface card, which transmit electrical signals.
The data link layer: it is responsible for splitting data into packets to be
sent across the connection medium such as cables, satellite and so on.
Network layer: it gets packets from the data link and sends them to the
correct network address, if more than one possible route is available for
the data to travel, the network layer figure out the best route.
Transport layer: though the network layer routes data to its destination,
it cannot guarantee that the packets holding data will arrive in the correct
order or that they will not pick up any errors during transmission, it is
the transport job to make sure that the packets have no errors and that
they are also received in the correct order.
Application layer: it contain the application that the user uses to send or
receive data, without layer the computer and its user would never be able
to send data and would not know what to do with data sent by another
user.

Internet layer:
 It responsible for basic network connectivity. When mapped to
TCP/IP layers the internet protocol or IP works with network
layer.
 In networking there has to be physical location to send data or
receive data from.
 To make this happen every physical location must have unique
network address this address is called IP address, hence every
computer on TCP/IP network must have an IP address which is
unique to that computer.
 This IP address can be compared to postal address that identifies
the exact location of the residence or cooperate house, just as two
residences cannot have the same postal address so also no two
computers on TCP/IP network can have the same IP address.
 The structure of an IP address is set of numbers separated by
periods, an IP address is 32-bit number divided into two sections,
the network section and the host section, addresses are written as
four fields , eight bit each separated by period, each field can be
number ranging from 0 to 255, this method addressing is called
dotted decimal notation.
An IP address looks like
field1.field2.field3.field4
All hosts/networks interfaces (NIC card) on the same network use the
network number; each host/network interface (NIC card) on the same
network must have unique host number.
The four fields of IP address are clubbed together into two sections , the
network number and the host number depending on the type of the
network the host or the network belongs to.

There are three types of network on the internet:
Find the class of each address:
a. 227.12.14.87 b.193.14.56.22 c.14.23.120.8
d. 252.5.15.111 e.134.11.78.56
Solution
a. The first byte is 227 (between 224 and 239); the class is D.
b. The first byte is 193 (between 192 and 223); the class is C.
c. The first byte is 14 (between 0 and 127); the class is A.
d. The first byte is 252 (between 240 and 255); the class is E.
e. The first byte is 134 (between 128 and 191); the class is B.

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