The computer industry's power comes from the ability of one machine to communicate with another. For a long time this was technically quite difficult, but now systems have been set up to make networking much simpler; however the underlying structure is much the same as it was decades ago.
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The largest network is the Internet, linking billions of devices across the world, estimated at 8.7 billion devices in 2012 with predictions of 15 billion by 2015. There are only 7 billion people in the world!. How does it work?

What is a Computer Network?

A computer network is a group of devices that are linked together using physical media (wires or fibres) or using wireless protocols (sets of rules). Each device is called a node and the connections are called links. Various devices are used to enable computers to communicate across a network.

Network Types

there are two main types of networks
  • Peer-to-peer or
  • Client-Server

Peer to Peer
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A group of devices that are linked together where no one device is more significant.
Each device is responsible for storing its own files and every device can communicate with all other devices.

A client-Server or Server Based Network has one or more devices that perform critical functions like file storage, permission control or running large applications. In these networks a server usually provides Internet access as well.

Recently this third form of network has begun to gain popularity. An individual or
Cloud Computing
Cloud Computing

business purchases services from an independent organisation which then hosts data, applications and other services on devices that belong to the independent organisation. This is cheaper for the business and provides security by having the cloud services based on multiple devices, perhaps across the world.

Small-scale networks are called LANs (local area networks). Large scale networks are called WANs (wide are networks). The internet is an enormous WAN.

Network Topologies

Topologies are the "shapes" of networks and often refer to how devices are physically connected. Some examples are
  • Bus
  • Ring
  • Star
  • Mesh
  • and Hybrid
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A Bus topology has a single cable backbone with a terminator at each end. Computers "hang off" the backbone and signals travel the full length of the backbone before being absorbed by the terminator. Computers read the signals as they go past. bus topologies are cheap to set up and run, but difficult to problem-solve.
A Ring topology is like a bus in a circle so needs no terminators. Each workstation regenerates the signal so it stays strong, but a break can bring down the whole network and be difficult to isolate. Newer ring topologies have partly overcome this problem.
Star topology has all computers connected through a central hub or switch. Networks based on a star topology are easy to add to, and failure of one branch only affects one device. They are easy to maintain but if the hub fails then the whole network goes down.
In a Mesh topology every device is physically connected to every other device. This makes the network very stable as one break has little effect. They are very expensive, however, and difficult to manage because of the number of connections.

Most networks are Hybrids, for example combining multiple Star topologies with a central bus or ring.

Wireless topologies are now becoming more common. Wireless Access Points (or cells) transmit and receive wireless signals
with computer devices over a limited range . The Access Points are then connected to the cabled network so it can communicate with any part of it.

Network Protocols

Protocols are a set of rules that allow manufacturers to produce devices that will talk to each other. The most important are Ethernet and TCP/IP.

  • Ethernet over twisted pair is the protocol for the creation of wire cables and connectors. Similarly there is wireless protocol called IEEE 802.11 that covers wireless communication within a local area network.
  • TCP/IP stands for Transmission Control Protocol/Internet Protocol. It controls how computers communicate, how data is sent and received, cut up, transmitted and reconstructed.

Watch this video for information on how a wireless network connects to the Internet via TCP/IP

Internet Transmission

Computers communicating over a network produce an enormous amount of "traffic", some of which involves large files. If this traffic was like vehicles on a road then many of the signals would be significantly delayed, waiting for large road trains to pass. To allow messages to be transmitted simultaneously they are broken up into packets which are transmitted with information about the computer that is sending them, the computer they are being sent to and the file that they belong to. This allows the message to be received successfully and then reconstructed. See this illustration.

You can find this and more information at this Udemy link.

For a detailed coverage (beyond what we need) go to this Networking Concepts link.

Network Issues
The Internet is such an important global WAN that there are important issues to be considered in understanding its use. The Network Issues page provides a brief discussion and some useful tools for tracking messages.