Internet

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1 Definition

  • Internet is a network of networks that relies on the Internet Protocol.
  • Wikipedia defines “ The Internet [as] the worldwide, publicly accessible network of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP). It is a "network of networks" that consists of millions of smaller domestic, academic, business, and government networks, which together carry various information and services, such as electronic mail, online chat, file transfer, and the interlinked Web pages and other documents of the World Wide Web. (retrieved 20:48, 28 March 2007 (MEST)).”
  • Sometimes (e.g. in the press) Internet is a synonym of the World Wide Web (WWW), which is clearly not very precise. The WWW is accessed through Internet, but so are Email or on-line computer games.

See also: Internet history

2 Internet defined by an RFC addressed to Schools

RFC 1941 - Frequently Asked Questions for Schools (1996) defines Internet in the following way.


The Internet is a large and rapidly growing worldwide network

comprised of smaller computer networks, all linked by a common protocol, that enables computers of different types to exchange information. The networks are owned by countless commercial, research, government, and education organizations and individuals. The Internet allows the almost 5 million computers [...] and countless users of the system to collaborate easily and quickly either in pairs or in groups. Users are able to discover and access people and information, distribute information, and experiment with new technologies and services. The Internet has become a major global infrastructure used for education, research, professional learning, public service, and business.

There is a confusing variety of types of Internet access. These types of access are distinguished either by the services one can use (telnet, Gopher, FTP or File Transfer Protocol, World Wide Web) or by the technology underlying the access (the protocol, or rules the computers must follow in order to communicate with one another). The Internet is most clearly defined by its technology, but other technologies now offer access to many of the same Internet services, most notably electronic mail and the World Wide Web. The most important question for a user today is probably not "Am I on the Internet?" but "Do I have access to the Internet services I want?"


This text written in 1996 is still relevant. Current Internet has rather 500 Million connected computers and some services like Gopher are now almost extinct, but the confusing variety rather dramatically increased. E.g. just to understand the basics of video streaming one needs to talk to an expert.

3 Architecture of the Internet

Usually, one identifies five layers (also called the Internet protocol suite:

3.1 The Physical Layer

  • Various sorts of cables that directly connect computers (mostly Ethernet coaxial or optical fiber cables). Today, one finds mostly:
    • Fast Ethernet (100 Mb/s), in a typical older building (1995)
    • Gigabit Ethernet, in modern buildings, between buildings, organizations and in the backbones of most networks (since 1998). Recent networking cards in desktop computers also support Gigabit (Apple's powerbook since 2000).
    • 10 gigabit Ethernet, between major very modern HUBs (2002)
    • 100 gigabit Ethernet (experimental in 2006)
  • Connection via telephones and modems
  • Wi-Fi
  • ....

3.2 The Data link layer

This is the layer which transfers data between adjacent network nodes in a wide area network or between nodes on the same local area network segment. E.g.

  • Ethernet (mostly at work, but also in some homes)
  • PPP or more recent DSL (e.g. ADSL) over telephone lines, mainly used to connect a Home network to rest of the world.

Over the same physical layer, one can can run several kinds of data links. (E.g. the now extinct AppleTalk local networking system was based on "LocalTalk")

3.3 The Network layer

In essence, the network layer is responsible for end to end (source to destination) packet delivery, whereas the data link layer is responsible for node to node (hop to hop) packet delivery. (Wikipedia)

The best known protocol is the Internet Protocol (IP). It breaks down a message to packets and can send them over through several nodes over a heterogeneous network (e.g. a mix of Ethernet, Wi-FI).

IP provides an unreliable service, i.e. data can arrive corrupt, out of order, be lost etc. Errors must be repaired at the next level, e.g. with TCP.

have to insert something about addressing and packet structure

3.4 The Transport Layer

The Transport Layer is the second highest layer in the four and five layer TCP/IP reference models. It directly answers to the application layer and makes requests to the network layer and usually turns the unreliable and very basic service provided by the Network layer into a more powerful one. E.g. it can ensure that data arrive in the right order or can request that lost data are sent again.

The best known layers are TCP and UDP.

  • The Transmission Control Protocol (TCP) can create connections between two hosts (computers), over which they can exchange streams of data using so-called Stream Sockets. The protocol guarantees reliable and in-order delivery of data from sender to receiver. It can distinguish data for multiple connections by concurrent applications, e.g. you can at the same time surf on the Web, receive email and be connected to a virtual world. Typically, HTTP (World Wide Web) servers use TCP and below IP. The combination of both is called TCP/IP.
  • The User Datagram Protocol (UDP), also called Universal Datagram Protocol or Unreliable Datagram Protocol can send short messages sometimes known as datagrams. It does not provide the reliability and ordering that TCP does. Datagrams may arrive out of order, appear duplicated, or go missing without notice. However, this makes UDP faster and more efficient for many lightweight or time-sensitive purposes, e.g. video streaming.

3.5 The Application Layer

At this level, there are standards that define messages and data formats understood by specific applications running at each end of the communication.

Examples (there are many more !!)

  • Hypertext Transfer Protocol (HTTP), the underlying communication protocol of the World Wide Web that specifies how a web server and a navigator talk to each other.
  • File Transfer Protocol - FTP
  • Simple Mail Transfer Protocol - SMTP (the de facto standard for e-mail transmissions across the Internet)
  • Dynamic Host Configuration Protocol - allow a device (e.g. your computer at home or sometimes at work) to request and obtain an IP address from a server which has a list of addresses available for assignment.
  • Real-time Transport Protocol (see video streaming).
  • Simple Object Access Protocol (SOAP), one of the protocols that define how servers can talk to each other by sending XML-based messages.

4 Internet in education

4.1 Technical aspects

At the technical level there are several avenues for which the reader may have an interest (and not all are necessarily specifically educational technologies, e.g.

4.2 Conceptual aspects

For conceptual issues, either follow up the links in the technical articles or start with the Instructional design model article or the educational technology article which attemps to give an overview of the field.

5 Links

Wikipedia includes an Internet portal that includes links to most conceptual and technical articles.

6 References

Sellers, J. and J. Robichaux (1996). Request for Comments: 1941 - Frequently Asked Questions for Schools, Internet Engineering Task Force (IETF), HTML