Internet

Draft

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 19:12, 28 March 2007 (MEST)).”

• Sometimes (e.g. in the press) Internet is a synomym 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

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, 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.

Architecture of the Internet

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

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
• WIFI
• ....

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 at work
• PPP over telephone lines

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")

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. (http://en.wikipedia.org/wiki/Network_layer 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

References

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