Transcript Lecture 2

IS1811 Multimedia Development
for Internet Applications
Lecture 2: The Internet and the World
Wide Web
Rob Gleasure
[email protected]
http://girtab.ucc.ie/rgleasure/index.html
IS1811

Today’s class
 History of the Internet
 History of the World Wide Web
 The process of browsing
 The basics of physical networks
The Internet

Where did it all begin?
 Communication between computers existed before the Internet.
In the late 50s/early 60s primitive “bridges” joined pairs of
computers on some networks

The US Dept. of Defence Advanced Research Projects Agency
(DARPA)
 Interested in feasibility of making communications nuclearstrike resistant
 People began to realise the potential of computers from a
communication perspective
 ARPANET
The Internet

ARPANET
 Throughout the 1960s Connectionless Packet Switching had
been developed – ARPANET was based on this

In 1969 a connection between the University of California and the
Stanford Research Institute was established, based upon the
ARPANET technologies. Other American universities followed
and the number of connections grew swiftly.

By the early 70s there were a lot of different networks around with
a lot of different standards. Also, UNIX and low-cost computing
arrived in the mid 70s, paving the way for copyleft and the open
source movement.
 this created a need for a simple common protocol so they
could interact.
The Internet

TCP/IP
 DARPA combined Network Control Protocol and Internet Protocol
into a new layered architecture called the Transmission Control
Protocol/Internet Protocol (TCP/IP)

Not long after TCP/IP appeared in 1974 it became ARPANET’s
only approved protocol. It’s widespread use and adoption allowed
direct links to form between other existing networks and
ARPANET itself
The Internet

The NSF
 During the 1980’s, the National Science Foundation (NSF) began
the project of connecting all government and educational facilities
in America. To do this, the NSF added further infrastructure
(NSFNET), which further aided the expansion of the network

NSF promoted Internet usage amongst campuses
 5 Supercomputer centres developed made resources
available for scholarly research

Advanced Networks and Services (ANS) were formed to run
NSFnet in 1990, which established gateways to other networks
enabled such as BITnet, DECnet, etc.
 NSFNET was eventually bought by AOL in 1995
The Internet

So who pays for the Internet?
 Everyone pays for their own part of it, NSF pay for NSFnet,
NASA pay for NASA Science Internet
 Individuals (you and me) pay an Internet Service Provider (ISP)
for their connection

Who runs it?
 There’s no one person or group in charge as such
 The Internet Society (ISOC) is made up of volunteers who
promote global information exchange and manage technical
direction.
The World Wide Web
The World Wide Web

CERN (European Centre for Nuclear Research)
 In 1989 and 1990 Sir Tim Berners Lee documented his idea for a
WorldWideWeb, with help from Robert Caillau

Whereas the Internet exchanged data, the World Wide Web was
being envisioned as a way to exchange information

Berners Lee combined The hypertext idea and Transmision
Control Protocol to create Hypertext Transfer Protocol (HTTP)

He also described the Browser-Server approach and proposed
methods for their implementation.
The World Wide Web (continued)

Berners Lee saw the need for a standardised system for
accessing and presenting information

This standardised system had to be simple, so it could be used
across a range of systems, both high and low end

After a successful test-run viewing a number of pages, other
researchers began designing primitive browsers


Mosaic, the first complete ‘proper’ web browser was introduced in
1993 by the National Center for Supercomputer Applications
(NCSA)
This browser was made compatible with Windows and Macs and
a huge boom in usage occurred
The World Wide Web Consortium
W3C

The W3C was founded by Berners Lee in 1994

Established as an industry consortium dedicated to building
consensus around Web technologies

Develops open web standards and guidelines

A vendor-neutral forum
 Standards based on royalty-free, available to all technologies
The World Wide Web Consortium
W3C

The W3C recommend and support a number of technological
standards, based upon these ideals. These include a number of web
authoring tools, such as:
 HTML, XHTML & CSS
 JavaScript, PHP, SQL, & Ajax
 XML, XSLT, XML Schema

These technologies are all tied together by the Document Object
Model (DOM)
The Document Object Model (DOM)

The Document Object Model
 Developed/being developed by W3C
 http://www.w3c.org/DOM/

Breaks documents down into components, which then makes it
easier for programming languages to manipulate content

Defined at a high level so that a variety of languages can be used
with it
Structure of the Internet

Basic assumptions in a network
 The network is unreliable
 There must be more than one path from A to B!
 Any computer can communicate with any other computer
 Only a minimum amount of information is needed by the
computers before they can “talk”.
Common Types of Network

LAN (Local Area Network)
 Computers are connected together within a "local" area (for
example, an office or home)
 Ethernet is a very common form of LAN

WAN (Wide Area Network)
 Computers are farther apart and are connected via
telephone/communication lines, radio waves, or other means of
connection

MAN (Metropolitan Area Network)
 Rare but does exist
Client-Server vs. Peer-to-Peer

Peer-to-Peer





A network where all computers have more or less the same
responsibilities (shared burden!).
Inexpensive and straightforward to set-up and manage.
Very difficult to manage
security matters.
More difficult to deal with
shared information (who has
master copy?) and ensure
that common technologies
are used, etc.
Commonly used in file-sharing
websites.
Client-Server vs. Peer-to-Peer

Client-Server






A network where certain computers act as dedicated providers of
resources to some number of full-time client computers, i.e. certain
computers are
“full-time clients”, others are
“full-time servers”.
More conducive to growth.
Removes burden for client
machines.
Enables uniformity.
Better for security.
Requires quite a bit of
technological expertise.
Basic Concept of Web Browsing
Hardware Components of a Network

File Server (in Client-Server networks)
 A very high capacity computer (fast and with a lot of memory) that
sits at the heart of a network.
 The network Operating Systems (e.g. Windows Vista, Linux, etc)
and any other shared software are stored on this computer.
 Must be able to store vast amounts of data and share it very
quickly.

Connection types, cables, etc.
 Twisted pair, fibre-optic, etc (beyond the scope of this course…)
Hardware Components of a Network

Switches
 Switches are a simple type of device used to link several LANs
and route packets between them.

Repeaters
 When a signal travels along a cable, it tends to lose strength. A
repeater is a device that boosts a network's signal as it passes
through.
 Used when the length of a network cable exceeds the
standard maximum set for that type of cable.
Hardware Components of a Network

Hubs
 provide a central connection point for devices in a network, a hub
will contain multiple ports.
 Commonly used to connect segments of a LAN.
 Simple but only suitable at smaller, local levels
 Just sends information received to everything!
Hardware Components of a Network

Bridges
 Simple inexpensive means of segmenting 1 network into 2 or
more (provide a yes/no entry mechanism).
 Why?
 Maintains good performance in each part of network
without letting unnecessary traffic through.
 May connect networks with various different types of
cabling (but they must use the same protocol).
Hardware Components of a Network

Routers
 Translates information from one network to another – located at
Gateways where networks connect.
 Know the address of other routers, computers and bridges on
the network.
 select the best path for data based on its origin and
destination.
 Routers are clever things - similar to a super-intelligent bridge!
 Can listen to the network to see what parts are busy
 Can avoid collisions, decide when “back-roads” or other
unusual routes would be more desirable.
 Most common means of connecting a network to the Internet
(often bundles all the functionality required).
Hardware Components of a Network

Almost a very loose progression as we get more local in our network
 Routers  Switches  Hubs and Bridges
(not always the case, as was already mentioned
routers often bundle most of the functionality)
Want to read more?




“The Computer as a Communication Device”, J.C.R. Licklider and
Robert Taylor 1968
(http://gatekeeper.dec.com/pub/DEC/SRC/publications/taylor/licklide
r-taylor.pdf)
“As We May Think”, Vannevar Bush 1945
(http://www.theatlantic.com/past/docs/unbound/flashbks/computer/b
ushf.htm)
http://www.w3.org/
http://www.isoc.org/