World Wide Web Aaditya Bhatia CS 147

Agenda History OSI model Hardware IP address DNS Server - Client Peer-to-peer Web-Sites Web programming Search engines Questions?

History 1960's o US DoD develops the world's first packet-switched network, ARPAnet, for resistance against nuclear attack. o First Universities gain access and inter-connections. 1970's o NSFNet developed o More Universities added to the network 1980's o The first commercial and private ISPs gain access to the network 1990's to Present o Technological advances increase individual access and perpetuates the internet's exponential growth.

OSI Model

TCP/IP vs OSI Not exactly the same Only 4 layers in TCP

Hardware Network Adapter Hub Switch Router Gateway Modem

Hardware - Network Adapter Connects a computer to another device Deals with OSI layers 1 and 2 Ethernet Wired o 10 Mbps o 100 Mbps o 1 Gbps Wireless o a o b o g o n

Hardware - Hub Connects multiple devices Doesn’t manage packets Packet Collision Relatively slower

Hardware - Switch Layer 2 device Routes packets Packets don't collide Much faster Telephone exchange

Hardware - Router Creates an internal LAN Outer network - single IP Layer 3 device NAT - Masks the internal machines Routing table Wired or wireless

Hardware - Gateway

Hardware - Modem Modulator – Demodulator OSI layer 1 Relatively Slow Economical

IP Address Unique identifier 4 octets Assigned by o ISP o DHCP server o Network admin

DNS Domain Name System Address resolution Analogous to an phone book hostname => IP address

DNS - IP lookup

DNS - Address resolution

Server-client mode Request Response e.g. a website

Server Dedicated machine Serves multiple clients Handles incoming requests Provides services

Client Invokes remote services Generates request A workstation

Peer-to-peer Peers - equal Act as a server and a client Invoke and provide services e.g. BitTorrent

Web-Sites Web server o Apache Web browser o Firefox HTTP Protocol o Stateless connection o Simulated statefulness  Cookie  Server-side session

HTTP Protocol Stateless connection Simulated statefulness o Cookie o Server-side session

Web Programming HTML CSS Server Client AJAX

Web Programming - HTML HyperText Markup Language Content of websites Server response Understood by Browser Static content

Web Programming - CSS Cascading Style Sheet Defines style of a page Easily changeable or replaceable "Themes" CSS sample: p { color: red; font-size: 18px; }

Web Programming - Server Server side scripting o PHP o Perl o Python Programs that execute on server Access o Database o Internal systems Efficiency o Servers are faster

Web Programming - Client Client side scripting o DHTML o JavaScript Make changes to page after it has loaded o periodically o based on user input JavaScript sample: document.write( " Hello World " ); for( i = 0; i < 10; i++ ) alert( "Hello again " + i );

Web Programming - AJAX Asynchronous JavaScript And XML Update only a part of page with server's response Avoid multiple refreshes Lesser network traffic Example: Yahoo! Mail Counter example: SJSU eCampus

Search Engines Help find information Web pages Locations News Images etc. Crawl throughout the Internet Gather information continuously Key role in advertising market o Context-based ads

References

for your patience

Questions?