Background

History

The Internet refers to a collection of thousands of computer networks exchanging information according to specific rules or protocols. The WWW refers a large collection of documents accessible via the Internet. The history of the Internet and the WWW Convergence of two major ideas (i) Internet protocols and (ii) hypertext.

Internet (1969)
- ARPANET (Advanced Research Projects Agency NETwork)
  Department of Defense wanted a network that could function even if some connections were destroyed. There is no central authority since that would make the entire network vulnerable to attack. The network was based on the idea of packet switching. Messages sent over the network are broken down into packets which take different routes from the source to the destination. If one of the nodes is down, the packets can be rerouted and communication can be maintained. The internet was used as a communication and research tool by the military and in academia.
- History of Internet from 1836 to 1997
- Packet switching theory (Leonard Kleinrock Ph.D. thesis)
- Roads and Crossroads of Internet History
- Net TimeLine
WWW (1992)
- CERN (European Council for Nuclear Research)
  Up until the 1990's it was challenging to use the internet as a communication device. The WWW as developed by Tim Berners-Lee at CERN. His immense contributions include (i) URL - a scheme for giving every document on the internet a unique address (ii) HTML - the language for encoding and displaying hypertext documents (iii) HTTP - the set of rules allowing hypertext documents to be linked across the internet and (iv) the first web browser. Berners-Lee then made his inventions freely available to the public.
- WWW history by Berners-Lee

Internet protocols

The suite of internet protocols is divided into seven layers.

(1) Physical	Concerned with the transmission of bits and deals with issues such as the number of bits per second to be transmitted and the voltage levels representing 0 and 1.
(2) Data link	Handles errors in the physical level. Uses check sum. If the value of checksum is incorrect, requests retransmission.	ARP RARP
(3) Network	Handle address assignment and the transmission of packets. The packets are routed independently.	IP
(4) Transport	The network layer does deal with lost messages and the transport layer ensures reliable service.	TCP
(5) Session	Establishing a communications session. Passwords and security.
(6) Presentation	Provides independence from differences in data representation.
(7) Application	Protocols for higher level applications such as electronic mail, remote logins and file transfers.	Telnet, FTP HTTP, POP3/IMAP

TCP protocol - when messages are sent over the Internet, they are broken down into packets. Different packets may take different routes from the source to the destination. Each packet is labeled to identify the sender and the receiver and travels independently. Upon arriving at the destination the packets are reassembled.
IP protocol - This is the addressing system of the internet. Every host computer on the Internet has a unique IP address which is a string of four numbers separated by periods or dots. For example 162.15.189.32. Since each of the four numbers is represented using 8 bits, the numbers can range from 0 to 255. People rarely see these numbers because the Internet's domain name system (DNS) translates these numbers into more meaningful strings called domain names. Domain names always have 2 or more parts, separated by dots. The part on the left is the most specific, and the part on the right is called the top level domain (TLD). There are only a limited number of top level domains such as
- .edu
- - education
- .com - commercial
- .gov - government
- .mil - military
- .net - network organizations
- .org - nonprofit organizations
- Countries and their domain extensions
HTTP protocol - protocol for transferring WWW documents.
FTP protocol - file transfer protocol
Resources

Terminology

URL or URI (Uniform Resource Locator, Uniform Resource Identifier)
The URL contains the following information (i) How can the page be accessed? (ii) Where can the page be found? and (iii) What is the path (directory and filename) to the page? The general format of a URL how://where/what addresses each of these questions.
Example: http://www.pcwebopedia.com/index.html

Example: ftp://www.pcwebopedia.com/stuff.exe

Anatomy of a URL
Bandwidth - the rate at which information can be sent through a connection, usually measured in bits-per-second. A full page of English text is about 16,000 bits. A fast modem can move about 57,000 bits in one second. Full-motion full-screen video would need roughly 10,000,000 bits-per-second.
Terminology resources

Physical components

Servers - computers that respond to requests for services such as mail servers and news servers.
Routers - computers that direct data packets along the network (directing traffic).
Networks - Physical means of transporting packets of information including copper wires (electrical impulses), fiber-optic cables (light waves) and radio waves, microwaves,... which transmit messages through the air.

Connections to the internet

dial-up - allow a temporary connection using a modem and a phone line and have narrow bandwidth (56 Kbps).
direct - many schools and business have a direct connection to the internet through a LAN. Includes T1 (1.544 Mbps) and T3 (44.736 Mbps) connections with very high bandwidth.
broadband
- DSL - digital subscriber line (6.1 Mbps)
- Cable modem (27 Mbps)
- Satellite connections (1.2 Mbps)
- wireless broadband (20 Mbps)