Transcript How the Internet/Web Works

44212: Web-site Development
How the Internet/Web Works
Ian Perry
Room: C49
Extension: 7287
E-mail: [email protected]
http://itsy.co.uk/ac/0506/Sem1&2/44212_WSD/
How does the Internet work?
 Just like any other Network!

Hardware provides physical structure:


cables (copper & fibre), hubs, switches,
routers, servers, satellites, plus the client
computers themselves.
Software facilitates the exchange of data
(communication) over physical network:

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Software that enables networking follows a set
of rules; a protocol.
44212: Web-site Development: How the Internet/Web Works
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What are Protocols?

Rules for communication


to understand & act on messages sent/received,
computers at both ends of the ‘conversation’ must
agree on what a message means.
Description for each type of activity

e.g. establishing a remote connection, exchanging
e-mail, or transferring files, requires agreed
definition of:


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the format that messages must take.
how messages must be transmitted.
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‘Snail-mail’ Protocols
 The ‘Rules’ that govern how we address letters, and
how the Post Office handles those letters:
Mail Box
The rules (protocols) of the Postal System
ensure that a properly addressed letter
(format) will reach its destination via a
delivery route (transmission).
Post
Office
Train/Van
Destination
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Post
Office
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Protocols = Interoperability

For the Internet to
be really useful:
– different types of
computers, using
different operating
systems, must be
able to connect, &
communicate with
each other.
– they can, as long as
they conform to
Internet Protocols.
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44212: Web-site Development: How the Internet/Web Works
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The Internet Protocol

TCP/IP


a suite, or family, of protocols;


Transmission Control Program / Internet Protocol
enabling messages to be correctly formatted and
transmitted from computer to computer
irrespective of computer type/operating
system.
How many of you can speak Esperanto?

TCP/IP = Esperanto for Computers
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44212: Web-site Development: How the Internet/Web Works
Slide 6
Other Internet Protocols

File Transfer Protocol (FTP)


Simple Mail Transfer Protocol (SMTP)


to send e-mail.
Post Office Protocol (POP3)


to transfer files between computers.
for retrieval & management of e-mail.
HyperText Transfer Protocol (HTTP)

to transmit Web-pages over the Internet.
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44212: Web-site Development: How the Internet/Web Works
Slide 7
Internet = Client/Server Network

Client/Server?


a networking model consisting of a series
of requests and responses.
Client Programs


Server Programs


make requests & format responses
‘answer’ requests & provide responses
Very efficient in sharing a limited
resource (i.e. Bandwidth) with many users:

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connections only formed ‘as-and-when’ required.
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Client/Server Transactions
 File Transfer (via FTP)

Client program contacts an FTP Server and
requests transfer of a file; FTP Server responds
by transferring the file to the Client’s computer.
 E-mail (via SMTP & POP3)

Client program allows user to interact with an email Server to send (SMTP) and receive (POP3)
electronic mail messages.
 Web (via HTTP)

Client program request the contents of an HTML
page from a Web Server; and displays the result,
as a Web-page, on the Client computer.
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Slide 9
Internet Addressing
 People/Computers communicating via
the Internet need to know where they
are located, i.e. their ‘address’.
 The term “address” is used somewhat
loosely on the Internet, and might
refer to:

a ‘computer network’, a ‘computer’, a
‘software application’, a ‘file’, etc.
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Slide 10
IP Address = ‘Real Address’



All ‘intelligent devices’ on the Internet
(i.e. every computer, router, switch,
etc.) must have a unique IP Address.
An IP address consists of four
numbers, between 0 and 255,
separated by dots.
Sometimes called a ‘dotted quad’.

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e.g. 150.237.176.24
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Domain Name = ‘Human-friendly’

Domain Name Servers

maintain a distributed database; the

e.g. the Domain Name:
Domain Name System (DNS)
 Match ‘human-friendly’ Domain Names
to ‘real’ IP addresses.
www.hull.ac.uk

is a lot easier to remember than:
150.237.176.24
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Internet Domains

The Internet’s domain name system
‘describes’ a hierarchy of domains.
 Top-Level-Domains (sector/country)
.com, .edu, .co.uk, ac.uk, etc.

Sub-Domains (organisation)
ibm, mit, eyms, hull, etc.

Servers (service)
www, pop, ftp, etc.
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E-mail Addresses


Email Addresses identify both a person and
the sub-domain of the e-mail Server that
stores their messages, e.g.:
[email protected]
Reading from left to right:
i.p.perry = mailbox for this Person/User.
hull
= who works for this Organisation.
ac.uk
= which is an Academic Organisation
located in the United Kingdom.
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44212: Web-site Development: How the Internet/Web Works
Slide 14
What is the Web?

Basic components are:



a Client (i.e. Browser), requesting HTML documents.
the Internet, providing a communications channel.
a Server (i.e. Web Server), with access to a store of
HTML documents.
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Slide 15
Web Addresses

Relies upon Uniform Resource Locators (URLs)
protocol://server.sub-domain.top-leveldomain/directory/filename

Example URL:
http://www.hull.ac.uk/home/index.html

Often a URL does not need to include
directory/filename:
http://itsy.co.uk/

URL might not ‘request’ an HTML document:
mailto:[email protected]
ftp://src.doc.ic.ac.uk/
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Slide 16
Next Week’s Workshop
 Next week’s Workshop asks you to locate &
analyse the Web-sites of organisations that
are ‘similar’ to ABM Car Sales.

To see if anything can be learnt (borrowed?)
from the experience (mistakes?) of others.
 You have all read ABM Car Sales Case
Study, haven’t you?

If not, then make sure you do before next
week.
Ian Perry
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Slide 17