THE INTERNETThe 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
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