The term network is used in many different arenas. Examples of networks are social networks, phone networks, television networks, neural networks, and, of course, computer networks. A network is a system of connected elements that operate together. A computer network connects personal computers (PCs), printers, servers, phones, cameras, and other types of devices. A computer network connects devices in a way allowing them to exchange data among each other, which facilitates information and resource sharing. At home, computers allow family members to share files (such as photos) and print documents on a network printer, televisions can play movies or other media stored on your computers, and internet-enabled devices can connect to webpages, applications and services anywhere in the world.

In the business environment you have a lot of business operations marketing, sales, and IT. You need to develop apps that allow information to be collected and processed. Computer systems that collect and process the information need to communicate with each other in order to share resources. You also need an infrastructure that supports employees, who need to access these resources and interact with each other. A network allows multiple devices such as laptops, mobile devices, servers, and shared storage to exchange information with each other. There are various components, connected to each other that are necessary for this communication to take place. This infrastructure allows a business to run, lets customers to connect to the business (either through salespeople or through an online store) and allows a business to sell its products or services. To run normally, at the end of the day, a business and its applications relies on networking technology.

A computer network can exist on its own, independent of other computer networks. It can also connect to other networks. The internet is an example of many networks interconnected together. It is global in its span and scope. To operate successfully, interconnected networks follow standardized rules to communicate. These rules are accepted and adhered to by each participating network.

The early internet connected only several mainframe computers with computer terminals. The mainframe computers were large and their computing power was considered enormous (albeit being the equivalent to today’s mobile phone). Terminals were simple and inexpensive devices, which were used only to input data and display the results. Teletype is an example of such a device. The range of devices that connects to internet has expanded in last decades. The internet now connects not only laptops, smartphones, and tablets but also game consoles, television sets, home systems, medical monitors, home appliances, thunder detectors, environment sensors, and many more things. The earlier concept of centralized computing resources is revived today in the form of computing clouds.

Computer network engineers are people who design, develop, and maintain highly available network infrastructure to support the information technology activities of the business. Network engineers interact with users of the network and provide support or consultancy services about design and/or network optimization. Network engineers typically have more knowledge and experience than network technicians, operators, and administrators. A network engineer should update their knowledge of networking constantly to keep up with new trends and practices.

Users who wish to connect their networks to the internet acquire access through a service provider’s access network. Service providers’ networks can use different technologies from dial-up or broad-band telephony networks, such as ADSL network, cable networks, mobile, radio, or fiber optic networks. A service provider network can cover large geographical areas. Service provider networks also maintain connected between themselves and other service providers to enable global coverage.

Computer networks can be classified in several ways, which can be combined to find the most appropriate one for the implementation. Local and remote networks are distinguished by the distance between the user and the computer networks the user is accessing. Examples of networks categorized by their purpose would be data center network and storage area network (SAN). Focusing on the technology used, you can distinguish wireless or wired networks. Looking at the size of the network in term of the number of devices it has, there are small networks, usually with less than 10 devices, medium to large networks consisting of tens to hundreds of devices, and very large, global networks, such as the internet, which connects thousands of devices across the world.

One of the most common categorizations looks at the geographical scope of the network. Within it, there are local-area networks (LANs) that connect devices located relatively close together in a limited area. Contrasting LANs, there are wide-area networks (WANs), which cover broad geographic area and are managed by service providers. An example of a LAN network is a university campus network that can span several collocated buildings. An example of a WAN would be a telecommunication provider’s network that interconnects multiple cities and states. This categorization also includes metropolitan-area networks (MANs), which span a physical area larger than LAN but smaller than WAN, for instance a city.

Medium-to-large enterprise networks can span multiple locations. Usually they have a main office or Enterprise Campus, which holds most of the corporate resources, and remote sites, such as branch offices or home offices of remote workers. A home office usually has small number of devices and is called Small Office/Home Office (SOHO). SOHO networks mostly use the internet to connect to the main office. A main office network, which is a LAN in terms of its geographical span, may consist of several networks that occupy many floors or it may cover a campus that contains several buildings. Many corporate environments require deployment of wireless networks on a large scale and they use Wireless LAN Controllers (WLC) for centralizing management of wireless deployments. Enterprise Campuses also typically include a separate Data Center which is home to the computational power, storage, and applications necessary to support an enterprise business. Enterprises are also connected to internet and internet connectivity is protected by a firewall. Branch offices have their own LANs with their own resources, such as printers and servers, and may store corporate information, but their operations largely depend on the main office, hence the network connection with it. They connect to the main office by a WAN or internet using routers as gateways.

Networks support the activities of many businesses and organizations and are required to be secure, resilient and to allow growth. The design of a network requires considerable technical knowledge. Network engineers commonly use validated network architecture models to assist in the design and the implementation of the network. Examples of validated models are Cisco three-tier hierarchical network architecture model, spine-leaf model, and Cisco Enterprise Architecture model. These models provide hierarchical structure to Enterprise networks, which is used to design the network architecture in a form of layers (for example LAN Access, LAN Core), with each layer providing different functionalities.

All the exchange of data within the internet follows the same well-defined rules, called protocols, which are designed specifically for internet communication. These protocols specify, among other things, the usage of hyperlinks and Uniform Resource Identifiers (URIs). The internet is a base for many other data exchange services, such as e-mail or file transfer. It is a common global infrastructure, composed of many computer networks connected together that follow communication rules standardized for the internet. The protocols and processes of the internet are defined by a set of documents called Request for Comments (RFCs).