What is a computer network?

Lesson

Networks are made up of network nodes (endpoints, switches and routers) which use interconnections to communicate with each other and move data from one device to another. Network components may be structured in a number of different topologies depending on the size and purpose of the network. For example a home network will look very different to an enterprise network which could span multiple offices across the globe.

To make it easier to build networks using many components, potentially from many different manufacturers we split it into layers. The lowest layer includes the medium used to transmit ones and zeros across physical space – for example an Ethernet cable or some form of wireless technology. The highest layer includes applications such as a web browser which turns the data transmitted across the network into something useful. We use two models to represent networks, the Open Systems Interconnection (OSI) model and the TCP/IP or Internet Protocol Suite model.

Each layer will implement one or more protocols as a means of communication. A protocol is simply a set of rules which all parties follow in order to understand each other. For example, let's look at a protocol analogy for social etiquette:

• Party A initiates communication with “Hello”
• Party B acknowledges this with “Oh, Hello”
• Party A asks “How are you?”
• Party B replies “Good thank you.”
• Party B reciprocates “How are you?”
• Party A replies “Good too, thank you.”

Free flow conversation is now free to happen until either party decides to close the conversation:

• Party B initiates the close of the conversation with “Well, must be off. Bye!”
• Party A hears the “Bye” and reciprocates, thus closing the conversation. “Bye!”

Devices on a network, like the people in our analogy, will only communicate successfully if they both adhere to the same protocol.

The core protocols in use today, including the Transmission Control Protocol (TCP) and the Internet Protocol (IP), date back to research carried out for the US Department of Defence and at US universities in the 1970s and 1980s.

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