THE INTERNET

The Internet is the worldwide "network of networks" that links millions of computers together via copper wires, fiber-optic cables, wireless connections, and other telecommunications channels. It is a massive network of networks, a networking infrastructure, forming a network in which any computer can communicate with any other computer as long as they are both connected to the Internet. Information that travels over the Internet does so via a variety of languages known as protocols.This publicly accessible network of interconnected computer networks communicate using a set of protocols and standards, the most basic of which are TCP/IP. TCP/IP consists of the Transmission Control Protocol in conjuntion with the Internet Protocol. Other protocols such as DHCP, DNS, FTP, HTTP, IRC, MIME, POP3, SMTP, SSH, TELNET, RTP and many more help hold the whole thing together.
This learning resource will look mostly at the technical aspects of the Internet, but may eventually cover social, economic, historical and other aspects.
A popular way to visualize the complexity of the Internet is to see it as a stack of layers known as the OSI model, short for Open Systems Interconnection model.

OSI Layers:
* Layer 7: Application Layer – the main interface for the user(s) to interact with the application and therefore the network
* Layer 6: Presentation Layer – transforms data to provide a standard interface for the Application layer
* Layer 5: Session Layer – controls the dialogues (sessions) between computers
* Layer 4: Transport Layer – provides transparent transfer of data between end users and machines
* Layer 3: Network Layer – provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks
* Layer 2: Data Link Layer – provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the physical layer
* Layer 1: Physical Layer – defines all the electrical and physical specifications for devices and the communications media

HARDWARE: Topologies

bus

All nodes are connected to a single wire or cable (the bus) which has two endpoints. Each communications device on the network transmits electronic messages to other devices. If some of those messages collide, the sending device will wait and then try to transmit again. The advantage of bus network is that it is can be organized as a peer-to-peer network or client/server network.
It is also relatively inexpensive to install.
The disadvantage is that if the bus network fails, the whole system network fails.
The wider the bus the better!

ring

The ring network is a network in which all communications devices and microprocessors are connected in a continuous loop. Electronic messages pass around the ring until they reach the correct destination; there is no central server.
The advantage of a ring network is that messages only flow in one direction.
The disadvantage is that if a single connection is broken, the whole network stops working. The distributed star or tree topology can provide many of the advantages of the bus and the star topologies. It connects workstations to a central point, called a hub. This hub can support several workstations or hubs which, in turn, can support other workstations. Distributed star topologies can be easily adapted to the physical arrangement of the facility site. (Integrated Publishing)

star

A network that links all microcomputer and other communication devices through a central server.
The advantages of this hub is that it prevents impact between messages. The network forms a star shape having the central server in the middle with a single branch outward, the branch will not branch to another device.
Other Advantages Include:
* Good performance.
* Scalable, Easy to set up and to expand.
* Any non-centralised failure will have very little effect on the network, whereas on a ring network it would all fail with one fault.
* Easy to detect faults
* Data Packets are sent quickly as they do not have to travel through any unnecessary nodes.
* It is used for centralised control.