a network

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introduction

When three or more things are connected together to share a resource, you have a network. A bar room full of people, the national power grid and the Internet are networks.

We only care about the computer variety of network because we have no friends. Computers draw electricity from a power network and share information using a data network. If someone mentions a network that has something to do with computers, they are talking about a data network.

Different types of network are described by their attributes: their layout, the distance they cover, the components or cables used, and so on.

what it is

simple network hardware
simple network
network
computer
computer
network cable
NIC
NIC

The simplest computer network is two computers that can talk to each other. Some hardware things and some software things are required to make a computer network.

Connecting two computers in a simple computer network takes several bits of hardware: two computers, a NIC (Network Interface Card) in each computer and a network cable connecting the two NICs. Networks connecting more than two computers contain network computers such as repeaters, routers, bridges, switches and hubs.

Each computer in the network also needs several bits of software: programs to control the NICs and programs that can communicate using network protocols.

There is a model that gives a picture of what the hardware and software is doing when it sends and receives information. This is called the OSI (Open Systems Interconnection) 7 layer model. Since most of the communication is done behind the scenes most people happily use networked computers without knowing the OSI 7 layer model even exists. Most home and office networks use the ethernet protocol for the lower layers and the TCP/IP suite of protocols for the upper layers. TCP/IP is the most famous set of protocols because this is used all over the Internet. TCP/IP describes how to send little packets of data across a network.

The diagram above is a network topology. People often define a network by the shape it makes in a topological diagram.

People also define a network according to the distance it has to cover. Home and small office networks are LANs. MANs and WANs are used by big companies.

networks defined by distance
abbreviation name description
LAN Local Area Network LANs are small, such as a half dozen computers and a printer. The LIC is a LAN. The organisation network is another LAN.
MAN Metropolitan Area Network A MAN typically gives high bandwidth over a few miles. A company that uses several buildings in one city may rent a MAN.
WAN Wide Area Network Computers in different towns and countries form a WAN. The Internet is an enormous global WAN.

There are a few different types of network cable found wiring up the Internet. The type of cable found in homes and small offices is UTP (Unshielded Twisted Pair).

A person who looks after the network is called a network administrator. A network administrator is part of a support team. A system administrator makes sure that computers run properly and a network administrator does the same for the network.

what it isn't

TCP/IP. Networks are often referred to as TCP/IP networks. TCP/IP is a suite of protocols that describe how computers in a network can talk to each other. It is not a type of network.

where it is

All the computers in the LIC are linked to form a network. So are all the computers in the enterprise and all the computers in the Internet.

history

In the 1850s Samuel Morse gave up his portrait painting career and had a roaring success with a new type of telegraph. In the 1870s Emile Baudot added digital communication and multiplexing.

In 1876 Alexander Graham Bell and Thomas Watson reeled out two miles of telegraph cable and had a telephone conversation.

In the 1960s Bell Labs invented the modem and sent digital information across the analog telephone network.

In 1965 Lawrence Roberts and Thomas Merrill connected a computer in Massachusetts and a computer in California using a telephone line. The WAN was born.

Up to this point pretty much all communication was done using circuits. Norman Abramson broadcast packets using a satellite in 1972. He lived in Hawaii and called it the Aloha system. Perhaps he didn't fancy calling it the Hula Skirt system.

In the 1970s the Xerox PARC (Palo Alto Research Center) looked at the Aloha system and invented the ethernet. Ehternet LANs are now found just about everywhere.

In the 1990s the Token Ring protocol was developed by IBM.