Internet, web & HTML Week 12
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Internet, web & HTML
Week 12
W h a t i s i t ?
•• Internet ≠ web and email!
•• Internet = the structure that allows web, email and other services to run
•• Physical part: wires, radio waves etc
•• Logical part: protocols like TCP/IP
•• Speed of network = bandwidth
•• Bandwidth = number of bits transferred pr second
T h e T C P / I P p r o t o c o l
•• A protocol is a set of rules and a ‘language’ that governs communication
•• TCP: Transmission Control Protocol
• Governs the timing and safety of the data transported
•• IP: Internet Protocol
• Governs the addressing of the data
•• TCP/IP makes sure data traffic on the internet:
• Flows with minimal chance of losing data
• Arrives with minimal chance of data corruption
• Is uniquely addressed, and can be tracked back to the sender
P a c k e t s
•• To send data over the internet, it is broken down into
Packets
•• A packet can be of varying length, but always contains:
• The recipient address
• The sender address
• The packet number
• Many other control meta tags
• Several bytes of the data
Hi! In reg…
Address to: … from: …
Subject: …
Return
Address
Packet
#
Data
…
I P - n u m b e r s
•• The IP number is the address
•• Every computer on the internet has a unique IPnumber
•• 4 bytes long, written out like 4 groups of base 10 numbers
129.240.200.1
•• First two numbers identifies network
•• Last two identifies computer in sub-network
S e r v i c e s O v e r v i e w
•• There are several distinct services available on the internet, amongst which are:
•• Email for personal, time skewed messaging
•• Web for rich information browsing
•• FTP for password protected file up/downloads
•• Telnet for computer remote control
•• IRC for real-time community chat
•• Peer-to-peer for personal, real-time chat
•• Usenet for time skewed community messaging
C l i e n t – S e r v e r
•• Most services uses a communication model based upon the client – server idea
•• Client initiates, sends requests to servers
•• Server waits, serves clients
•• There are several variations possible
•• The server is just another piece of software
U R L s
•• Standard form of addressing on the net
•• URL: < service >://< domain >/< filepath >
•• Service identifies which service we use
•• Domain : address to the server we want to reach
•• Optionally, filepath specifies the exact file we want to reach on the server
W h a t i s a w e b p a g e ?
•• Web pages are nothing but basic text documents
•• Can be created in any text editor
• Notepad
• TextEdit
•• Images etc are stored external to the document
•• HTML
• defines the format (information hierarchy)
• defines the functionality (feel)
• provides the links to external resources
•• HTML was not intended to specify the looks of pages
H T M L
•• Hypertext Markup Language
•• Open-platform page description language
•• Text document with tags and pointers for structuring documents and linking to external resources
•• Client computer formats HTML document for display
C o m m o n H T M L t a g s
•• <TITLE>The title tag creates a page title on the top of the browser</TITLE>
•• <BODY>The rest of your HTML is placed here </BODY>
•• <P>drops the line down a paragraph
•• <BR>creates a line break
•• <A HREF="http://WWW.COWAN.EDU.AU"> Follow this hypertext link to ECU</A>
•• <A HREF="mailto:m.mcmahon@cowan.edu.au">click here to mail me</A>
C o n t e n t v s S t r u c t u r e
H T M L – A d v a n t a g e s
•• Small file sizes
•• Does not require expensive authoring tools
•• Web space is inexpensive
•• Does not require programming skills
•• Provides links to external resources
•• Once uploaded, provides “Instant Publication”
•• Can be viewed on any computer with free web browsing software
H T M L - D i s a d v a n t a g e s
•• What you design will not necessarily appear the same on every computer!
•• Several versions of the HTML standard
•• Different browsers support different/unique HTML tags
•• Different hardware affects final result
•• Not designed for precise layout or multimedia
•• Hypertext only provides limited interaction
H a r d w a r e C o n s i d e r a t i o n s
•• Not all computers can support graphics or even use mice!
•• Monitor Size & Resolution
• Large graphics will be truncated on small monitors
•• Colour Depth
• 16 bit images will appear degraded on a 256 colour system
W W W B r o w s e r s
•• Initiates the transfer of information from the server to client
(browser)
•• Renders the information as web pages in the browser
•• WWW browser software supports features such as:
• Display of HTML and plain-text documents
• Display of GIF, JPEG and PNG files within HTML documents
• Display of other media files through plug-ins
• Transfer of files from server to client computer
• Enabling the user to fill forms and submit on-line for processing on the
WWW server host
• Form fill-in functionality requires special software on the server
E x t e n d i n g f u n c t i o n a l i t y
•• JavaScript
• Provides interactive functionality to the HTML elements on a web page
• Written in as commands at the start of the HTML file
•• Plug-ins
• Provides multimedia in an area of a web page, animation/video/sounds etc
• Handled by third-party programs ‘plugged in’ to the web browser
•• CSS
• Rules for the visual presentation of elements of a web page
• Define once, use anywhere
• “New” standard
• Helps separate the presentation (visual) description from the structural
T h e p h y s i c a l I n t e r n e t
•• How is traffic sent from one computer to the next
•• Nodes: Hubs, Switches and Routers
•• Hub:
• Unintelligent, simple
• Connects several computers to each other
• Can connect ‘upwards’, to the rest of the net
• All packets sent from one computer to the hub is sent to all the other ports on the hub
• Inefficient, insecure, generates a lot of unneccesary traffic
• Usually unmanaged
N e t w o r k - f u n d a m e n t a l
N e t w o r k - H u b
N e t w o r k - R o u t e r s & D N S
•• Routers:
• A kind of ‘SuperSwitch’
• Usually closely managed
• Provides effective network management for high traffic nodes
•• DNS – Domain Name Servers
• Translates IP numbers into Domain names (like bjorknes.no)
• Every computer on the internet knows the address of at least one
DNS
• Makes the internet more human friendly
N e t w o r k - R o u t e r s & D N S
N e t w o r k - t r a f f i c f l o w
N e t w o r k - t r a f f i c f l o w
I n t e r n e t o r g a n i z a t i o n
•• The physical Internet has no top node
•• Top level is interconnection between each countries routers
•• There is stricter hierarchy on the organization side
•• IANA is the top controlling body for IP number assignment
•• ICANN is the same for Domain Names
•• Organizations are non-profit, often collaboration between nations.
