Over time, the desire to implement the first computer network, as a result of curiosity, had already been converted to a need that would fulfill the requirements. Precisely, it also led to the development and advancement of computer networking technologies. Thus, the need to connect and interconnect more computers into computer networks, and with it, more locations, in itself resulted as the need to define topologies, architectures, technologies, and computer networking categories. In this way, the types of computer networks like PAN, LAN, MAN, and WAN were born.

A PAN is defined as a computer network that is used to connect and transmit data among devices located in a personal area, usually over Bluetooth or Wi-Fi to interconnect devices (see Figure 1.2). Occasionally, this computer network is called a home area network (HAN) too:

To understand the LAN, let's compare it with the PAN. A PAN is dominated by portable devices (for example, smartphone), while a LAN mainly consists of fixed devices. Both computer networks are covering the local area; however, the LAN has a greater coverage than the PAN, because the LAN usually can cover the floor of the building, several floors of the building, an entire building, or even a few buildings that are close to one another. From that, the main difference is that a PAN is mainly organized around an individual, while a LAN is organized around an organization, business, or legal entity. This then precisely defines the LAN as a computer network that connects two or more computers in a local area for the purpose of sharing resources, as in Figure 1.1.

From the standpoint of coverage, the MAN is bigger than the LAN and smaller than the WAN, whilst from the viewpoint of data transmission speeds, the MAN is faster than both the LAN and WAN. As it was with the PAN and LAN, the reason for the MAN's existence is the need for sharing and accessing the resources in the city or metro. From that, a MAN represents a group of LANs interconnected within the geographical boundary of a town or city, as in Figure 1.3:

Areas that are not covered by a LAN or MAN are covered by a WAN. Thus, a WAN is a computer network that covers a wide geographic area using dedicated telecommunication lines such as telephone lines, leased lines, or satellites. That being said, unlike other computer networks which have geographic restrictions of their physical reach, WAN does not. From that, it is obvious that WANs are made up of PANs, LANs, and MANs (see Figure 1.4). With that in mind, the best example of a WAN is the internet:

The intranet is a networking platform primarily designed for employees. That said, it is considered to be the private network of an organization where employees can access network services. The intranet is not just a portal; instead, it is a network that consists of hardware and software too. To better understand it, consider the intranet as an organization's extended LAN, or MAN, or even WAN network. It consists of multiple cables, network devices such as switches, routers, microwave and satellite antennas, access points, servers, computers, and various applications. All that enables employees to communicate, develop content, collaborate in joint projects, and get the job done.

In contrast, the extranet can be thought of as an intranet with a controlled access. Like the intranet, the extranet is a networking platform too; however, besides employees, the extranet enables controlled access to an organization's intranet for authorized partners, suppliers, customers, or others business-related individuals and organizations outside the company. Specifically, the extranet represents a controlled access method of the organization's intranet using internet infrastructure.