A network is an assembly of interconnected devices (PCs, servers, mobile devices, routers, switches and so on) that can communicate (exchange information) with each other.
Networks can be of several types:
1. LAN or a Local Area Network, such as your home network connected through cable.
2. MAN or a Metropolitan Area Network such as an extended network between computers on the surface of a city
3. WAN or the Wide Area Network such as the Internet
4. WLAN or a Wireless LAN such as your wireless network from your own home.
A computer network is made up from:
1. End-devices (PCs, laptops, smartphones, servers and so on)
2. Switch – interconnects multiple end-devices in a network
3. Router – interconnects multiple networks
4. Firewall – protects a network from possible attacks from the Internet
5. Transmission medium such as cable (copper), light (fiber optic) or wireless (air).
End-devices
In general, in a network most people are just the ones that have an end-device. Every person that has a Laptop, PC or smartphone with which it connects to the Internet is called an end-user. This connection can be made by 1 or more transmission media (UTP cable, light, air).
When we connect with a smartphone to the Internet, most likely we will use the wireless environment. If we use a Laptop, we can link it either by wireless or UTP. The fiber optic connection is generally used when we want to connect network equipment or servers to each other (e.g., switch – switch, server – switch ). The reason is simple: a fiber optic connection can be much faster than a UTP cable or a Wireless one.
Switch
The switch is a piece of network equipment that interconnects multiple PCs (in general but not limited to printers, IP phones, APs and so on) to the same local area network (LAN). It is characterized by a large number of ports (generally 12 to 48) all capable of speeds between 100 Mbps and 1 Gbps (or even 10 Gbps). The switch uses MAC addresses to identify each end device.
Router
A Router is a piece of network equipment that has the function of interconnecting multiple networks (LANs) into a more massive (WAN-Wide Area Network) network. The router is the device that connects most devices to the Internet. It handles packet delivery to the destination Internet network.
Compared with a Switch, the Router has far fewer ports (between 2 and 8) at similar speeds (100 Mbps up to 10Gbps, depending on the model).
To communicate, digital devices (PCs, routers, switches) must have a unique identifier on the Internet, called an IP (Internet Protocol address). An IP is a way to identify a unique device in a network, as there cannot be two devices with the same IP in a network.
Inter-networking
Inter-networking techniques (inter-networking rather than the internet) connect two or more networks or network segments to each other using devices operating at the OSI system level 3, such as a router. Any interconnection between public, private, commercial, industrial or government networks can be called “internetworking.”
In current practice, interconnected networks use the Internet Protocol (IP) level. There are three types of internetwork networks, depending on who is managing the network and who has access to them:
1. intranet
2. extranet
3. Internet
Intranet and extranet networks may or may not have access to the Internet. If they are connected to the Internet, they must be protected against unauthorized access from the Internet. The Internet is not considered part of an intranet or extranet. However, it can serve as a way to access some portions of the extranets.