What is a Network?
A network is essentially a number of connected or interlinked devices. This website that you are reading now has crossed (probably) thousands of miles, multiple devices from the web servers to your device. These devices and the connections between them make up the structure of a network. There are a number of different technologies that allow for this transmission, from wireless radio frequencies to using light. The internet is made up of multiple ISPs peering with each other to forward traffic across the globe.
Beyond technologies, there are also a number of protocols that provide a standardised ruleset for how traffic should be processed, forwarded or transmitted across a network. During the journey that data takes to reach it's destination, it will be encapsulated and de-encapsulated many times per the OSI model. Encapsulation is defined as wrapping or enclosing something (in this case a payload of data) by adding headers and footers depending on the layer per the below.
An analogy of how a network operates, is to imagine a typical road network. Imagine that the cargo within a lorry is the data being transmitted, and the roads taken are the wiring. There are motorways that allow higher throughput (fibre optics), and country roads that allow lesser throughput (copper pairs). The truck itself is the packet, which ultimately moves the cargo (data) through the road network. The IP address would be the physical destination for the cargo (data), of which the truck might use navigation tools to reach it. This would not be dissimilar to the route-tables used across the internet for forwarding traffic. Each roundabout would send the truck down a different path, exactly how routers across the internet work together to move data.
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OSI Model
The OSI (Open Systems Interconnection) model was designed to ensure that the different technologies and protocols work together in a hierarchical fashion to ensure reliable and consistent transmission of data. It also provides for a structured approach to network design as without each of the 7 layers present, a website for example cannot be loaded.
You will also see engineers refer to issues as being a Layer 2 problem, or a Layer 3 problem which can narrow down the troubleshooting steps required. See below table for a short overview of each layer, the protocols you might encounter and a short description. Please note that some protocols are multi-layered (eg ARP).
TCP/IP Model
The TCP/IP model is very similar, however it simplifies the structure of the model by concatenating certain layers per the below:
LAN and WAN
There are many different acronyms used in networking, and commonly you will come across LAN and WAN to denote interior networks, and external networks (the internet). LAN or Local Area Network essentially stands for the network currently provisioned at a single site, such as an office. WAN or Wide Area Network is usually referred to as the internet.
On the back of typical home routers, you will see a number of LAN ports and a fewer number (usually just one) of WAN ports.
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Encapsulation / De-encapsulation
Below is a typical UDP packet encapsulation example. Don't worry about any terminology for now, as this will be covered more in later articles. Once an application on the client device as a requirement to send something to another device on another network, the payload is wrapped in different "containers" to facilitate the transmission across the network.
