IS1811 Multimedia Development for Internet ApplicationsLecture 2: The Internet and the World Wide WebRob Gleasure

R.Gleasure@ucc.iehttp://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 nuclear-

strike 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 ConsortiumW3C 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 ConsortiumW3C 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 straight-

forward 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/licklider-taylor.pdf)

“As We May Think”, Vannevar Bush 1945 (http://www.theatlantic.com/past/docs/unbound/flashbks/computer/bushf.htm)

http://www.w3.org/ http://www.isoc.org/